I need help with a Heating/Air Conditioning issue.

[DonJones]

I thought some one here said they were an experienced HVAC engineer or tech. If so I need help trying to make my home Central Air Conditioning/Gas furnace work right. lf not I need to be referred to someone who can help me figure out why the lower floor is always cold and hopefully find a fix.

It is a split level with an open stairway so the heat seems to rise to the upper level and the cool air seems to settle. My thought on the cause is that since the only cold air returns are upstairs the furnace/ Central Air Conditioning does NOT circulate the air from the lower level and thereby lets the heat pool upstairs and the cold accumulate in the lower level. Further I think putting a door at the bottom of the stairway will only make it worse because then there will be even less mixing of the air between the 2 levels.

My thought on the solution is to put a cold air return in the return ducting just before it goes into the furnace but not between the filter and the furnace. There is a lot of air flow potential between the lower level in general and the furnace is in an unfinished utility room that does not have a door in the opening from the hallway.

I need some one with a lot more practical knowledge and actual design and functioning of the systems.

Thank you for your help.

Good smoking.
http://www.marijuanapassion.com/forum/showthread.php?t=29666

 

[DonJones]

meds4me,

Okay, now why do you say to put it as far from the furnace as possible? Is it to avoid taking a chance on CO poisoning or something else?

We have one of those 95+% high efficiency sealed gas furnaces where the fresh air for the gas burner is plumbed in from outside. The furnace sits on the floor and the cold air return comes from along the upper level floor/ the lower level ceiling, drops down parallel to the furnace, makes a right angle turn runs horizontal about 6" into the furnace.

The picture is the cold air return at the bottom on the left and the furnace on the right.

The darn filter is in that little horizontal run between the downward cold air return duct on the left and the furnace on the right at the bottom of both the duct and the furnace, and is a bear to get out to change or clean. I'm thinking about putting the new return high enough that I can put another filter in over where I can get to it to clean or replace it. I was thinking about making the new filter run left to right at a downward 45 degree and put the grill right above it on the side away from the furnace so I can open the grill, reach in and grab the filter to change or clean the filter.

I was thinking about a few inches above the splice in the return, which would place the opening about 4' from the floor. What do you think about that?

On the filters at the return vents, should they we fastened to the grill or just stood up in the part coming out to the grill?

Thanks for the help.

Good smoking

 

[tcbud]

Gonna bump this for you Don.
Good work on getting it all figured out.

 

[PencilHead]

Hold the scapel, Dr Jones. We've got freon-ies running around here somewhere--one'll come along directly and direct you.

But my $.02: Every 2 story I ever inhabited was always hot up/cold down, even in summer. Hate me a townhouse model.

 

[DonJones]

PencilHead,

I agree but not with this wide of temperature spread ( as much as a 25F difference).

Thanks for your reply.

Good smoking.

 

[snaxforgandhi]

Hey DJ,

I am not a HVAC engineer for sure, but I don't know that we need one here. I did work in the heating industry for several years and was once W.H.E.R.F. certified as well as being listed on the National Gas Workers Registry, so I have a fair idea of how these things can go.

You mentioned that the only cold air returns are located upstairs; though it can seem counterintuitive, this is pretty much S.O.P. I don't know what you do and don't know, so if I am telling you something you already know at any point please forgive me, I do not mean to condescend. That said, we sometimes misinterpret the term "cold air enchange/return," intuiting that the function is to conduct the "colder" air to the heat exchanger to then be heated. In other words, we see the relationship to be one of relative temperatures. In fact, the function is to balance pressure differentials that occur when air is conveyed through sealed ducting from one (relatively) airtight space to another (relatively) airtight area. They might more accurately be called "pressure equalization vents." Anyway, I only mention this to be sure we're on the same page. If you already knew it, dynamite.

Since, in a two-storey dwelling with fairly unobstructed air flow avenues between floors, air will rapidy convey itself along the vertical cline, engineers will generally opt for returns on the top floor only. As far as it goes, this is sound design since any positive pressure differential on the lower floor will resolve through the stairwell. The efficacy of this of course depends considerably upon just how open the floor plan is on each floor. But generally speaking, in a split level there is usually ample unobstructed cross-section to act as the return for the lower floor; hence, no dedicated ducting for return from the lower floor. Again, engineers generally get this right.

What they often get wrong (IMO) - either thru incompetence or by succombing to pressure by cost-considerations - is that they don't put enough returns upstairs. In a single level dwelling you can get away with this to some degree without the homeowner noticing as the imbalanced system needs only struggle with the pressure dif of one floor. Those of you in splits pay doubly for this practice though, as too few returns for the top floor becomes far too few to deal with both floors: Remember, circulated air only gets back to the heat exchanger inside the furnace by way of the returns, just getting the air from downstairs to up isn't enough. So, though I cannot say with certainty as I am not there to see it, this may be at least a part of the problem. In a perfect world, every space with an hot air register would have a strategically place cold air return.

If you have access to a sensitive handheld manometer, or even a digital barometer (maybe), you can map the "velocity" pressure difs throughout your home (All outside doors/windows closed). Most heating/cooling contractors and outfitters simply rely on formulas and building code to provide a balanced system, but a manometer provides a real-world map. If you're getting dramatic difs between upstairs and down you have a return gripe from downstairs. If your velocity pressures are equal, but significantly above 50 pascals then you probably don't have enough return cross-section, or "duct-area," to service the heat exchanger. If I had to guess (and I am) this is what I would suspect given the propensity of contractors to scrimp and the inaccuracies inherent in the just-go-with-the-numbers method of system design, coupled with the effect-multiplier of a split-level home with these design inefficiencies.

Another point of measure would be the return duct itself, right before the fliter relative to direction of flow. You'd need a fairly oddball and expensive meter called a magnahelic, however, and so it might not be very practical. If you can get ahold of one you would drill a small (avg. 0.125") hole in the ducting where indicated, and insert the meter's tubular probe. The vacuum (more accurately, the apparent pressure dif between atmosphere inside and outside of duct), measured in millibars, could then be compared to the furnaces installation spec for return air column. I wish we were neighbors or something 'cuz I actually own a magnahelic and haven't had occasion to use it in fifteen years! And again, a vacuum significantly higher than the manufacturers spec would indicate a need for greater return cross-section.

Now, I read you posts several times and I was still a little unclear as to your idea regarding adding another return. I got that you were thinking to cut in right at the furnace, correct? In general i believe that this is sound thinking with two caveats: First. cutting in near the furnace is fine as long as it is ducted from the first floor; simply cutting in and installing a grill directly at the site (furnace) will do nothing to enhance the circulation characteristics between the lower and upper levels and, depending upon your floorplan, may create a "short-circuit" (yep, they're called that in the forced air game too ) between a/the register and a/the return vent. Second, a system originally designed with zero returns below the first level would have this factored into the forced (hot) air ducting, and opening a hole down low in the system might bollocks that all up.

Lastly, (and you already know this of course) PencilHead is quite correct, getting equal heating in multiple level-dwellings has been a problem since there have been multiple-level dwellings. I think that you a probably seeing a quantative effect stemming from all of these areas we've discussed. But, again, I would seriously investigate the possible need to open up the return cross-section upstairs.

I hope I have not botched this too badly. Like I said, I read the thread a couple times to try to get a decent handle on it, but I may have missed something in the translation.

Good Fortune!

~Snax (He Who Hopes To Help)

 

[DonJones]

snaxforgandhi,

I'm a little confused. You said, I think, that ideally each hot air area should have a return area of the same size as the hot air vent, correct?

But then you say that the returns should all be upstairs. I don't understand.
Oh, when the house was built and the furnace orginally installed, the downstairs was unfinished, would that have any effect on the diagnosis?

If I added a return vent to the downward duct from along the down stairs ceiling, how would I determine what the proper size would be and where to locate it in order to avoid the "short circuit effect you described?

I'll tryto measure the return sizes later today and post them for you. Do you need the size and location or just the toal area in comparison to the heat vents in the given areas?

I have to go now and take my daughter0-in-law ot work. Her tires are as bald as a baby's behind and we woke up to 6" of snmow. Fortunately, I have my sister's Jeep and snow tirees on our car, so she isn't totally screwed.

It is 6:04 AM here4 in spokane, WA.

Thans and good smoking.

PS: often the "workers" can do a better job of correcting problems than the engineers.

 

[snaxforgandhi]

Hi DJ,

it's a small world; I just returned from driving my daughter to school, we also woke up to 6" of snow. Huh, how 'bout that?

I apologize if I was unclear, let me attempt to rectify and clarify.

1. When I mentioned that in a perfect world every room with a register would have a return duct of equal cross sectional area I was being a bit glib. While it is quite true that, all things being equal, forced air systems would benefit from being designed and ducted this way from the get-go, I didn't mean to suggest that one attempt a retrofit to accomplish this in each room. What I meant was that, ideally, systems would be designed and installed this way initially, during the rough-in phase of construction.

I should also clarify that I was putting this too simply; I should have said that every room with a register should have a return of the same size, and be ducted in such a way that the whole system's return capacity and flow rate be equal to the output. At first glance, these two specs would seem to be mutually inclusive. But say your system employs an 11" x 13" trunk duct that heads two directions off of a 20" x 20" to 11" x 13" tee-joint. One leg goes to heat the eastern half of the house, the other to the west, and in total there are six 4" x 12" registers being serviced by these trunks. Now, each room also has a 4" x 12" return vent, but they are cut-in to a single 11" x 13" circuit duct that services all six returns by itself. Even tho there are an equal number of registers and returns, the return capacity is governed by a single trunk duct of a given area, whereas the output trunk splits the initial flow resistance of the great big 20" x 20" output "hole" between two trunk ducts (double the area of the return side truck) as it "tees" off in two directions. There is far greater trunk area on the distribution side of the system than there is on the return side, even tho registers and ducts are matched one for one.

2. Now to clarify why I said that any increase in ducted return area should be plumbed from upstairs: In a two-level home with a forced air furnace on the bottom level and all return ducting pulling from the top level, the logic is that the stairwell (or whatever) between the upper and lower levels acts as a virtual duct (of enormous size) conveying air from a positively pressurized lower level up to the upper level where it then shares the return ducting that is venting that floor. So, both levels have a return path; air flows from the lower level up the stairwell to the top floor where it eventually finds the return vents there, and the air being pumped to the top floor also uses these return vents. This is what I meant when I was talking about how contractors who don't provide adequate venting in single storey dwellings kinda double screw the split level folks who are ducted as tho their's were a single storey home.

Say your house was magically transformed to a rambler with no "downstairs." Everything upstairs remained the same, just now it's the only floor of a single storey home. Now, even as a single level home chances are that you may not have optimal return vent capacity, tho you might not notice 'cuz it's close enough for only one storey. Now, POOF! The bottom floor reappears, and tho it is ducted for hot air to the downstairs rooms, it is not plumbed for return duct at all. The only way back to the furnace is for the air to migrate upstairs by convection where it must now share the already possibly overburdened return ducting on the top floor. Make more sense?

If one were to increase the return vent area total, they would want to do from upstairs because to provide dedicated return ducting from downstairs would be to interrupt the natural convection up thru the stairwell. The question now is why would we care about that? As long as there is an adequate return capacity, who cares where it travels? Well, it's entirely possible that it won't make much of a difference, but since the initial design dictated that hot air rising up thru your stairwell was part of the plan, other design elements that may not be readily apparent may well be affected adversly by this change. It's a time-proven rule of thumb: If we change a aspect of any engineered system to compensate for a deficit (in this case possible lack of return capacity necessary to accomodate the return from both floors) and we have a choice, always choose the path that accomplishes the goal while impacting the rest of the system as little as possible. By adding ducting from upstairs we increase our overall return capacity while assuring that the designated (we assume) return path from downstairs (the stairwell) is preserved. Maybe the designer meant for the air rising from downstairs to collide and mix at the top of the stairwell and this mass would then be used in "X" fashion. Remove that flow and we might upset the balance to a greater degree than necessary to get what we want.

I would like to keep going on this right now and I know I haven't answered everything adequately, but unfortunately I must start getting ready for work. I will for sure check back to the thread as soon as I can this afternoon/evening when I get home, and try to help out then. Cool?

I hope that this post has at least helped clear up my initial post. Sorry for any confusion.

Talk to ya soon!

~Snax (He Who Must Go To Work... Yuk)

...PS: often the "workers" can do a better job of correcting problems than the engineers...

Aint that a fact!

 

[DonJones]

snaxforgandhi,

Actually you confused me more at the same time you clarified your first post. I understand that not only must the vent area be roughly equal between hot and return vents, but the cross sectional area of the two ducting systems must be roughly equal, correct?

Here are the vent specs measuring the opening in the louvered area rather than the size of the holes in the floors/walls.

Upstairs
228 square " heat 260 square " return

Downstairs
228 square " heat No returns

Doorway at bottom of stairs
2788 square " w/no doors

I'll also check the ducting.

On the return side there is a 16" x8" duct that is about 4 ' long on one side of the tee and about 9' long on the other end. The short leg has 52 square " of grill area located in the kitchen floor near the interior wall which is fed by 2 each 9.5" x 4" floor vents , one under the cabinets ducted out the front of the cabinet through a hole approx 10" x 4" in the kick board/toe board and a floor vent near the exterior wall right in front of the outside doorway and an additional 9.5 x 4 " floor vent in the living room near the exterior wall right under the window with the kitchen.dining/living rooms a common open area plus a 9.5" x 4" heat vent in the bathroom with no return to that area when the door is shut. The long leg has 208 square " of grill divided equally between two bedrooms that each have 38 square " of heat grill located under the windows through the floor approx 4" from the exterior wall.

The 16" x 8" return tee is feed into a 25" x 10" duct down to the floor wher it makes a 90 degree turn to a 25" x 16" short duct to the side of the furnace with a25" x 16" stage loading filter.

On the hot side, the duct out of the furnace is 19" x 16" at the furnace flaring out to 19" x 19" in about 12" where the central air evaporator is located and then feeds into the 16" x *' tee. Each end of the hot duct is approximately the same length with the same amount of vent area.

If you leave the doors to the downstairs bedroom and what is now my grow room open it will freeze you out both Summer (with the AC running) and Winter. In the Summer, even with the doors closed it will be about 60F downstairs and above 85F upstairs with the fan on continuous and even worse on auto,and that is with the AC running wide open. I attribute about 5Fof that to the floor and bottom 3.5' of the wall being underground. In the winter, you can't keep the downstairs above 55F auto and 60F on continuous with the doors open. With the doors closed and the fan on continuous the downstairs stays about 60F to62F with the upstairs at about 70F and the 2400 watts of HID lighting running in the day time. Our gas heat bill has drastically lowered but the electric has sure jumped with those lights running.


Hopefully this will help you understand the system better.

Something else that has me confused is all of the 2 story houses that I've lived in only had cold air returns on the ground floor and none on the 2nd floor, but they seemed to work just fine and to keep the temps more uniform than what this one does.

By the way what part of the country are you located in? I'm here in Spokane, WA.

Thanks again.

Good smoking

 

[snaxforgandhi]

Hi Don,

Hmmm, sorry for confusion... this is one of those things that would take about 5 seconds if we were sitting at the same table and I could draw what I'm talking about, but is fairly difficult to convey with words alone. But I'll try.

...I understand that not only must the vent area be roughly equal between hot and return vents, but the cross sectional area of the two ducting systems must be roughly equal, correct?...

Ok, it sounds like you got the gist of it: To put it very simply, if you have a great big trunk duct supplying hot air out to say, 6 registers, and you have a smaller return trunk being serviced by 6 return vents, you are going to have greater resistance on the return side even though you have the same number of heat registers and return vents due to the fact that the return trunk is smaller in cross-section than the output trunk. the whole system is a cycle, right? So the maximum rate of air flow in the system will be governed by the narrowest restriction; it's the "weakest link" principle.

...Upstairs
228 square " heat 260 square " return

Downstairs
228 square " heat No returns

Doorway at bottom of stairs
2788 square " w/no doors...

Since we're dealing with this problem "after the fact" from a design standpoint, attempting to engineer an exact solution will be difficult at best, and I don't think we need to in order to address the bulk of the problem. To elucidate: If, in order to fix your spaceship 100%, it would take a year, but to fix it 85-90% (enough to get back to Earth) by estimating and making intelligent guesses would take a week, we choose the latter. There are sooooo many factors just to calculate max velocity pressures - any bends, how tight the bend (90*, 60*, etc., etc) angled hallways, ceiling shape and height, furnace location, any reducers, etc., etc. - that to try to second guess every feature in the sytem become overwhelming. What we need to do is to identify the problem in general terms, and then make an educated stab at resolving it.

With that in mind, let's assume that all trunk ducts are at least adequate in area and we'll leave them alone for now. Looking at your vent and register areas only then, we see that you have a total of 456 sq/in of register for both floors, but only 260 sq/in of ducted return, all of it upstairs. Remember, the "virtual duct" of the stairwell only serves to convey the downstairs return air to the top floor, not all the way back to the furnace. Once upstairs that (downstairs) air has to compete with the upstairs return air to get back to the furnace via the 260 sq/in of ducted return.

THE (POSSIBLE) PROBLEM: INADEQUATE OVERALL RETURN CAPACITY MAY BE SYSTEMICALLY REDUCING VELOCITY PRESSURE, THEREBY REDUCING RATE OF CIRCULATION. THIS MAY BE CAUSING "STALLING" OR STAGNATION AS A RESULT OF UNRESOLVED PRESSURE DIFFERENTIALS.

So, linear troubleshooting tells us that, though it may not be the problem, it is a problem, and it appears to be the "squeakiest wheel" so it's a logical and educated assumption that we start there. Our weak link, then, is that there's close to twice the cross-section of output to return. Providing greater return sounds like a plan. We already got to this point I think. So, where to put it?

I suggested locating any additional return capacity upstairs because, given no other info and not being there to see it with my own eyes, this is the solution for greater return that compromises the original design the least. In your system, all the returns are upstairs... all we'd be doing is to increase the return capacity. We wouldn't be changing anything else. If we effect the return increase downstairs, we'll also be changing the overall flow path by reducing the volume of air coming up the stairwell from downstairs, savvy? And since neither of us know what effect this will have on system balance or circulation, prudence dictates that we take the path of least "disruption."

..Something else that has me confused is all of the 2 story houses that I've lived in only had cold air returns on the ground floor and none on the 2nd floor, but they seemed to work just fine and to keep the temps more uniform than what this one does...

This is, IMO, a far better design. Warm air finds its way upstairs all by itself. Locating the returns low in the system ensures proper circulation in that part of a house that's most difficult to keep warm; the bottom floor. Let the top floor take care of itself! Unfortunately this is not the case in your home, but we can take a lesson there and try something. Have you tried restricting the warm air to the top floor by partially closing the upstairs registers? How about closing them completely? It might be worth the experiment just to see if using all the velocity pressure in the system to heat the downstairs only will get those temps up down there. This would also serve to further validate our assumption that your system suffers from inadequate circulation: We're assuming that increased circulation downstairs is the ticket, and closing all the upstairs registers simulates (at least downstairs) this change without tearing into wall and cutting holes in ducts by increasing velocity pressures and reducing the load on the return ducting. Not a fix in itself, but a decent indicator, savvy?

As far as where to physically locate an additional return, again, hard to say with being there, but the rule of thumb would be to find a place that lacks a return but has a warm air register and a door. Say a bedroom or bathroom. I specified "with a door" 'cuz a closeable space with a register and no return is an over-pressure candidate. As far as avoiding a short-circuit, that'll be pretty much just common sense which you seem to possess in sufficient measure. Avoid any placements that put a return vent in a direct line with a register unless it's a least 15'-20' away. Kitty-Korner placement is best; register along south wall, return vent along east or west wall. You can even get away with having the return on the same plane as the register as long as there is sufficient velocity at the register to propel the air column deep into the room.

The size (in area) of any additional return vents should be aimed at resolving the existing deficit: You're lookin' at what, nearly a 200 sq/in deficit in return cross-section? So maybe more than one new return? I would think, however, that any significant increase would help, say a 9.5" x 4"? That'd be nearly 40 sq/in additional capacity. Maybe try one and see if the system responds; see if we're going in the right direction? Then, if we see any improvment, add another.

So, in broad strokes: We're looking to increase circulation (rate of flow) by identifying the narrowest restriction and opening it up some while remaining conscious of the original design and taking steps to minimize the impact to other design considerations.

...By the way what part of the country are you located in? I'm here in Spokane, WA...

Security considerations prohibit me from telling you the name of my city, but in code I can tell you that it begins with "S" and ends with "eattle." Shhhh... If you successfully decipher this code please tell no one!

Try that "shut all the upstairs registers" thing and let me know what you observe. We'll go from there, huh?

~Snax

PS. I just had a thought, is your return ducting baffled anywhere? If you have central heat and cooling you may have baffles in your return (or output for that matter) ducting to adjust for summer and winter conditions.

 

[DonJones]

Snax,

I'm learning a lot more than I ever wanted to know, but that's a good thing --I think.


Quote:
Originally Posted by DonJones
..Something else that has me confused is all of the 2 story houses that I've lived in only had cold air returns on the ground floor and none on the 2nd floor, but they seemed to work just fine and to keep the temps more uniform than what this one does...
This is, IMO, a far better design. Warm air finds its way upstairs all by itself. Locating the returns low in the system ensures proper circulation in that part of a house that's most difficult to keep warm; the bottom floor. Let the top floor take care of itself! Unfortunately this is not the case in your home, but we can take a lesson there and try something. That is basically what my thought was all along, put an large single return vent in the downward leg of the return duct and in effect ignore or even block off the upstairs returns. But will that also work with the AC in the summer -- just direct most, if not all of the cool air upstairs, and let it settle down into the downstairs?

On the closing the upstairs vents, (heat rather than return correct?) I have noticed that the 2 upstairs bedrooms with 1 heat vent 9'5" x 4" and 1 return of 13" x 8" straight down through the bottom wall plate into the top of the long leg of the horizontal return never have heated or cooled properly, at least in my opinion, with the doors closed. Could that be because the return vents are larger than the heat vents? The heat vents are near the exterior wall in the floor under the window and the returns are in the opposite interior wall at the floor level also in a slightly diagonal arrangement. That has always puzzled me.

For the first couple of years that we lived here there was a return of about 14.5" x3.5" in the wall between the kitchen and living room that fed into the duct where the current 13" x 4" inch one in the kitchen floor feeds now. The actual grill opening in the wall was much larger than that but it fed a framed box in the wall with that size opening through the bottom plate into the duct below the floor.

It was changed because the wall was moved into the house by about 2' to enlarge the kitchen and since the kitchen has an open "wall" between the dining/living room that is about 10' wide and floor to ceiling high, everyone agreed that it made no sense to tear the ceiling up downstairs to move the return and keep in it the wall instead of the floor since it would not increase the amount of vent area and would probably actually restrict it because it would introduce 2 90 degree bends into the flow path versus the current one of just going straight down through the floor right into the top of the return duct.

As to the baffle thing, so far as we can tell there are no baffles in either the heat or return ducts. The Central air was an add on and all that I can see is that they inserted the AC unit into the upward heat duct right on top of the furnace and before the TEE That runs length ways of the house and from which all of the heat ducts branch off in what appears to be approximately 8" round ducts with rectangular adapters at the end of the round ducts. It appears that each round duct comes out of the top of the rectangular horizontal duct with a 8" round elbow, but it is hard to tel because most of the downstairs has a finished ceiling.

I agree that it would be so much quicker and simpler to walk through the house where you could see what I'm trying to describe and not doing real well at it.

Good smoking

 

[DonJones]

Snax,

I just got to thinking -- if I cut the new return vent downstairs right into9 the side of the rectangular duct and it didn't help or maybe even hurt the performance, I could always close it off pretty easily with sheet metal and duct tape- probably the foil kind,or could I?

I'm thinking about a 22" square hole a few feet off of the floor so I can install and easier to clean/change filter between vent and the furnace. How high off of the floor can I put the return vent without creating stagnant air near the floor?

Just a quick thought which for me are some times better than dwelling on things. I think that is probably because my mind is working on it in the background without pressure.

Thank you again for your help.

 

[snaxforgandhi]

Hey DJ,

...if I cut the new return vent downstairs right into9 the side of the rectangular duct and it didn't help or maybe even hurt the performance, I could always close it off pretty easily with sheet metal and duct tape- probably the foil kind,or could I?...

Yeah, you absolutely could. And yes, I always use aluminum foil tape for ductwork, something my old boss believed in strongly.

You know, since we're talking easily reversible experimental fixes, if you could get ahold of a length of flexible ducting (you could even buy a 20'-30' length and return it later if you were careful with it) you could cut-in downstairs, like you said, and then move the other "open" end to various rooms/places downstairs, and even upstairs if it was long enough, and that would give you a way to determine immediately if an added return in whatever room/space you were in would help or not. Not only that, but you could pretty well pinpoint the location within the room too! Huh. Sometimes I amazed even myself! I don't know why we never did that when I worked in the field. I should'a thought of that years ago!

It'd also let you "prove out" whether or not a new vent would create a short circuit or a stall.

I'd use uninsulated 10" flex-duct for this. It's going for a little under $30.00 for a 25 foot length in my neck-o-the-woods. Again, if you're careful with it you could probably return it for a refund when you were through, yeah? Kinda shady, I know, but hey, money's tight and I'm sure that Lowe's or Home Depot will recover OK.

Give this some thought; it's a simple way to determine real-world results without having to hack into things or do a bunch'a oddball math.

...I'm thinking about a 22" square hole a few feet off of the floor so I can install and easier to clean/change filter between vent and the furnace. How high off of the floor can I put the return vent without creating stagnant air near the floor?...

Let's see, a 22"x22" square hole would give you 484 sq/in. of additional return. That's quite a bit more than your estimated deficit of 196 sq/in., yeah? I don't think that'll be a problem as the rate of return flow is a function of the velocity pressure exerted by the blower, but even if it did turn out to foul things up you could very simply and easily reduce the hole, right? I understand that you would use this "access/return vent" to make getting to your difficult-to-access filter easier, yes? So, even if the 484 sq/in. hole proved too large, you could simply devise a "block" to partially occlude the hole, making it whatever size we determined it needed to be. I'm picturing a 22"x22" square with a grill, and under that grill is (if needed) a square hunk of removeable sheet metal - we'll call it 23"x11" (if it was determined that the hole needed to be occluded by half, say) zip-scewed into place (See pic.) This way you maintain your maintenance access and can tune your return hole to whatever it needs to be. ("...tune your return hole..." Sounds kind'a kinky )

As far as where to locate it on the return trunk, you'd want to be as low as you can go (at least from a heating perspective, opposite for cooling unfortunately) without causing problems. For a rule of thumb: Velocity pressures upwards of 40-50 pascals should "churn" enough air in the room to allow a return vent within 24" of the deck. Anything above that and you'd be eating into warm air sooner is all, pressure-wise it doesn't matter at all (usually.) If you were to try the flex-duct experiment you could determine this in real-world by moving the end up or down and observing air movement. I always used to use a stick of incense for this in customer's homes, but a joint will work just as well! Anything that smokes a lot would do the trick, just something allow airflow to be seen.

Oh, and I agree about the overthinking stuff. I do it all the time! I can't help it. But, I'm pretty good about catching it and backing off. We can get too myopic if we're not careful, huh? That's actually how I thought of the flex-duct thing: I had stepped away from the computer and was chatting with my brats, and POOF! It just popped into my head. Duh.

Keep me posted.

~Snax

 

[DonJones]

Darn you're good, especially the illustrations. I envy anyone with thse kinds of skills.

The reason I was thinking along the line of the 22" x 22" hole was thinking also about just blocking off the upstairs returns and in effect creating the 2 story type system we discussed with no returns at all on the upper floor. The 22" x22" hole is only 28 square inches more than the total heat vent area.

If I go with the10" flex pipe idea, then I would need to cut in a 10" stub duct, split the end of the ducting, bend every other tab outwards at a 90 degree angle, insert the straight taps into the hole, and then bend them outward inside the rectangular duct by reach through the short round duct, correct? If so, how side should i make the tabs, about 1/2" or would 3/4" be better?

Thanks for the help.

Good smoking

 

[snaxforgandhi]

...Darn you're good, especially the illustrations. I envy anyone with thse kinds of skills...

What can I say? I'm a genius! (Ha!) Seriously tho, thanx for the kind words. I do OK with drawing software, but I can't draw a straight line on paper to save my life! If I draw a stick figure, folks ask "Is it a cantalope?"

...The reason I was thinking along the line of the 22" x 22" hole was thinking also about just blocking off the upstairs returns and in effect creating the 2 story type system we discussed with no returns at all on the upper floor. The 22" x22" hole is only 28 square inches more than the total heat vent area...

Yeah, it'd be easy enuf to test, huh? I'm thinking some cardboard and masking tape (so as to not ruin your wall paint.) You know, now that I think about it, if your returns are on the bottom floor then the system would actually try to pull warm air from upstairs to downstairs as the system attempted to balance itself pressure-wise, further countering the natural tendency of warmer air to concentrate on the top floor.

...If I go with the10" flex pipe idea, then I would need to cut in a 10" stub duct, split the end of the ducting, bend every other tab outwards at a 90 degree angle, insert the straight taps into the hole, and then bend them outward inside the rectangular duct by reach through the short round duct, correct? If so, how side should i make the tabs, about 1/2" or would 3/4" be better?...

Ya know, since it would just be for testing, I wouldn't even go that far. I'm thinking with a little thought we could avoid having to mess with a boot/transition/adapter at all. If we're pretty sure we're gonna cut into the return trunk at some point anyway, you could just cut a prelim hole and leave material for 4 makeshift tabs to bend out at 12:00, 3:00, 6:00, and 9:00.(see pic) depending on how good you are with tinsnips. It wouldn't have to fancy tho, especially if you're gonna wind up blowing the hole out to 22"x22" later anyway. The four tabs would provide more than enuf location and centering, you'd just have to worry about the air bleed 'cuz there's be no flange, but doing a "V" tape joint (easiest with cloth duct tape, the cheaper the better) around the circumference of the ducting would seal it to the trunk wall well enuf for testing purposes. And since it's on the return side it'd be a negative pressure duct and you wouldn't have to worry about "blow-out," it'd naturally try to suck in.

I realized too, after I posted that last one, that I wasn't specific as to "type" of flex-duct to conduct these tests; I was thinking of the helical wire and "fabric" (film) type 'cuz it's cheaper and more flexible than corrugated aluminum. And did I say uninsulated? That's what I'd use.

BTW, you are quite correct as to how to create a flange mount out of straight wall duct. I just don't want to see you spending any more money than you have to, especially for something temporary, yeah? I assume that, like my family, money isn't falling from the sky in Spokane.

I'm gettin' kinda jazzed now, eager to see what we get! For sure keep me posted!

~Snax

 

[DonJones]

Thanks.

One reason I was thinking about the normal entire circumference type fabricated "flange" was so I could do a DIY on fastening a round duct through a flat surface for ventilation in a grow area. I think it very likely that many of the members have no idea how to do it. Even though I know how to do it, I frequently rack my brain about it until I remember how they do it in HVAC sheet metal work. On a permanent installation, how wide should the tabs be?

We frequently read advice to duct the air flow from one place to another but I've never seen any one explain how to put a duct into a single layer wall or ceiling.

I'll let you know what I figure out.

Thanks again.

I sent you another PM about the MMJ issue.

Good smoking.

 

[snaxforgandhi]

...One reason I was thinking about the normal entire circumference type fabricated "flange" was so I could do a DIY on fastening a round duct through a flat surface for ventilation in a grow area. I think it very likely that many of the members have no idea how to do it. Even though I know how to do it, I frequently rack my brain about it until I remember how they do it in HVAC sheet metal work. On a permanent installation, how wide should the tabs be?

You're probably right, most folks aren't gonna know how to do that. As far as tab width, there's really no standard to reference, it's more an "eyeball" thing. But for a 10" round duct, I'd probably go the width of my left thumbnail, which is roughly 5/8". So, you're right in the ballpark with 1/2" to 3/4". Of course, the narrower the tab, the more "round" the union will be. I sure wouldn't go narrower than 1/2" 'cuz you want each tab to possess enough strength to maintain its deformation after being bent. Anything over 1" and your circumference will be too grossly "stepped" and you may have trouble sealing the union. So yeah, 5/8" to 3/4" is what I'd shoot for. A little non-hardening silicone RTV filleted at the union will help.

Something I tought of last nite as I was drifting off was that, since you looking at cutting-in a large return right on the return trunk, you may want to sandwich a volume damper in there somewhere. You'd probably have to build "out" from the trunk a bit to provide an enclosure for it, the mount the grill over the intake.

The reason I say this is 'cuz I'm still a tiny bit leery about making the "new" large return downstairs the only return. What I suspect will eventually happen is that you'll find a happy medium somewhere in the middle, having some return from above, most from below. Especially in upstairs rooms with doors (= sealed space,) an overpressure situation may develop that'd keep it from heating properly. In order to do this "tuning", however, you'll need some kind of quick damping. It would sure beat having to constantly change the size of any "blocking" plate over the return hole in the trunk.

...We frequently read advice to duct the air flow from one place to another but I've never seen any one explain how to put a duct into a single layer wall or ceiling...

Ya know, there just isn't an easy way to do that. This is why we see so much exposed ducting in older buildings. It's not that it can't be done, but it almost always involves rippin' into drywall, and then you have to re-route any wiring plus deal with the cat members and firebreaks between studs, etc., etc. It can be a real pain. One alternative to exposed ducting that our customers often opted for was to build chases that ran along the top of the wall, sharing two sides with wall and ceiling, sometimes wall and floor.

Keep me posted.

~Snax

 

[DonJones]

WSnax,

Thanks. Please explain what a volume damper is and where to find it. Are you speaking about the old fashion registers that had a single large plate behind the grill that could be adjusted to block off more or less of the duct area rather than the grill area?

Also, you might want to dazzle me with your drawing program some more and show the other readers who may not know what a chase is what the cross-section looks like and what they are. I know what you are speaking of but being able to explain it without an illustration is probably beyond me.

Do I want the new filter to be the same size as the old one and lay diagonally across the duct to increase filter area and thereby to lower the pressure gradient across it (air flow resistance)?

Gosh, the old Physics from high school is coming back. I haven't thought in, much less used, those terms for more years than some of you have been alive.

You know even if this project goes no where , it will be worth the mental stimulation!

By the way, what drawing software do you use and approximately how much does it cost?

Getting back to the subject, do you have any idea why the 2 upstairs bedrooms don't heat or cool properly with the doors closed even though each one of them separately has only 1/6th of total upstairs the heat vent area but each have one 1/3 of the return area?

Is that pressure gradient/imbalance thing why the bathroom with heat vent but no return vent gets so much hotter in the Winter and cooler in the Summer than the rest of the house when the door is shut? Personally I don't think it presents a problem because I think the door should be open unless the room is in use. That way you can tell at a glance whether or not it is occupied and whether you just need to head for the downstairs one instead.

I expect some comments about being gross or a lack of polish, but to me it is sure a lot more practical and it seems that people tend to keep any room cleaner when it is open to public view.

Good smoking

 

[snaxforgandhi]

Hey DJ,

There's a zillion different kinds of volume dampers, but the basics are a simple flapper or butterfly valve, or louvres. I attached a couple of photos. There's a guy on eBay making and sell just the round flapper and lever/handle parts so folks can make a volume damper out'a a hunk of simple straight duct/pipe. He's only askin' like $7.00 and the come in any size. Here's the link (remember to change the "XX" to "tt") hXXp://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320455255981&rvr_id=&crlp=1_263602_263622&UA=WVI8&GUID=a148aaeb1250a0aad4136273fb922e2d&itemid=320455255981&ff4=263602_263622

As far as the drawing program, I was using plain 'ol Windows "Paint." I do have some righteous drawing and CAD software for my other endeavors, but when I just need to do a quick shop drawing ('cuz I can't draw) I use Paint. It's quick and dirty, but does the job.

Speaking of that, since I know I can get better pictures than I can draw, I'll include some of chases in various stages of construction at the bottom of the post. But basically it's just a quick framework to provide a construct to hang drywall on. Since they're always cosmetic, 'cuz they're just "hides" and never load bearing, depending on your local building code (if you even bother to tell them, I probably wouldn't ) they can be 2x2s and box wood. How are your carpentry skills? If you can install a window, hang a door, or build a toybox, you're totally qualified to build a chase. (The horizontal ceiling duct chase image is from home theatre site and depicts detailed noise reduction measures, none of which you need to worry about. I included it 'cuz it's a great example of a horizontal ceiling duct chase)

You asked about filters: I always encouraged customers to modify their filter set-ups if they had forced-air. I won't mention brands or contractors, but too many are in cahoots with the filter industry (IMO) and design their systems with a perpendicular filter arrangement. Bah! You obviously had the foresight to see what I saw: Angled filters decrease flow restriction, increase the filter surface area, and increase filter life. So yes! If you can do it, mount that baby! I actually went a step further on my last system and I'm planning to convert my current system the same way; I use two filters arranged in such a way as to form a wedge, the sharp end facing toward the current. You used to see this in older systems where the engineers factored in a greater "funkiness" factor, usually on like oil furnaces that put crap in your air no matter how airtight the combustion and exhaust are. It creates oodles of surface area and drastically reduces restriction. But it requires the customer to have to reach up into the ducting and isn't as easy and clean as the perpendicular, slide-out style of today's crop. I'll throw in a pic of that down below too.

It's 3:00am here, so I'm gonna knock off for now and come back to it tomorrow, cool? I know I haven't addressed everything, but I will.

Take care DJ, talk to ya soon.

~Snax

 

[DonJones]

Is Paint one of the VISTA components?

I had a computer with AUTOCAD STUDENT version on it, but I'm afraid my son may have screwed up the WINDOWS 98SE OS trying to get XP installed on it so he could use the high speed cable Internet.

Snax,

Are 2 each 25" x16" filters installed in a tented arrangement enough or should I go bigger like 2 each 25" X 20"?

Also, is it okay To create a hinged door way through which to access the filers versus a sliding cover?

Currently the the vertical filter is installed/removed through a 1.5" wide, or narrower, slot type opening across the top of the horizontal ducting between the down duct and the furnace. It extends part way down the front side but it is very very awkward to work with because the slot is only 1/2", or less, wider than the filter. It is covered by a piece of flat ducting material with NO stiffening that slides inside what looks like the pieces you couple sections of rectangular ducting with and it is very difficult to open and close too because the fit between the slide and the slide guides is very tight and the slider is so floppy that it wants to bed and the edges are very sharp.

QUESTIONS:

Will it hurt anything to cut finger hold notches in the duct, so long as they are covered by the slider piece? That way I can get a hold of the filter and control it as I lift it out.

Also if I keep it located where the rivet heads line up with the slot in the duct surface, will it hurt anything to fasten a piece of angle iron to the outside of the slide piece to stiffen it up?

Is there anything to be gained by leaving the current vertical filter in and adding the tented filter set up stream of it or should I remove the current vertical one and just close off the opening? I could use the less expesnive fiberglass filters in the tented set and keep the stage loading on where it is or replace it with some other type of washable filter.

Thanks.

Good smoking