I need help with a Heating/Air Conditioning issue.

[snaxforgandhi]

Hola,

Yeah, Paint is just the resident draw app that has come with pretty much all the various incarnations of Windows (I think). The app itself is totally rinky-dink, but there's a wide network of Paint fans out there, and there are third party developers who, with Bill Gates' blessing, have built it into a quite powerful draw and edit program. hXXp://www.getpaint.net/index.html

If you're interested in drawing and drafting apps, I can highly recommend Visual CAD or Generic CAD for a CAD app, and Google's Sketch-Up for 3D work. I have used Auto, Visual and Generic CAD (though only Auto professionally) and I can say without reservation that Generic and Visual are orders of magnitude more intuitive than Auto. Visual CADD has my vote for price and versatility, as it also allows you to post process.

Google's Sketch-Up is free, and is probably the most powerful 3D drawing app in the world that is still easily and freely accessible to the everyman. I can't say enuf about this app, it just rocks.

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

Up to you Boss Either will give you oodles more area. In my last system I used two Filtrete Clean-Air 16"x25"x1" panels to replace the single 16"x20" stock filter. I should point out that when I used cheapy filters from Home Depot or wherever, they tended to want to collapse when they got full from the increased pressure. I was gonna mount a length of angle iron to support them (see pic), but I found that the Filtrete, being a name brand, had a more stout "frame" to it and didn't need the extra support. I'll probably mount side braces to my current system anyway though, just to be thorough.

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

You bet. hXXp://www.globalindustrial.com/g/maintenance/access-doors/access-doors/hinged-duct-access-doors

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.

Nope, won't hurt a thing. As long as you can seal it, pretty much any hole is cool so long as it is not compromising the structural integrity of the duct.

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?

No problem. One trick for keeping pop rivet holes from "bleeding" is to drill the hole thru both components, squirt a glob of RTV into both holes, then mate the two and rivet.

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.

I would say no, there's not much to gain by leaving the old perpendicular filter in, and a lot to lose in term of restriction.

Best,

~Snax

 

[DonJones]

Snax,

Thanks for the update.

I noticed your drawing now shows angle iron braces to support the filters. How heavy do they need to be and would running one along the apex of the filters alleviate the need to seal that joint every time the filters are cleaned or replaced?

Also, how air tight to the joints between the outer duct and the angle braces need to be as well as between the angle braces and the filters?

Am I correct that the steeper the pitch of the filters, the better it will be and the less restriction there will be due to the increased area available for air flow?

Thanks again and good smoking.

Please check the thread under MJ News on the latest Washington State legislative proposal for decriminalizing/legalizing possession of 40grams or less for anyone regardless of whether they are MMJ patients or not.

Good smoking

 

[DonJones]

Snax,

Are WEB ECO Lifetime washable filters as good as the stage loading stuff they used use?

Also, Looking into your end view drawing, where in relationship to the apex of the filter A-frame should the bottom of the new return vent be? If you can just add it to the drawing that will be okay. What I wondering is if the air coming in on the left side of the duct and having to flow to across the apex to reach the right filter is going to cause air flow problems.

Thank you again for your help.

Check on the MJ News for an update on the legalization bill you were taking about.

Good smoking.

 

[snaxforgandhi]

...How heavy do they need to be and would running one along the apex of the filters alleviate the need to seal that joint every time the filters are cleaned or replaced?..

Ya know, I say "angle iron" but that's the machinist in me referring to all metal stock as "iron." My bad. It actually doesn't require a great deal of strength. Back in the day I would have just used 1.75" strips of maybe 20 gauge sheet metal and bent them into L-stock on the brake. But that's kinda hard to get just right without a brake, so I would probably now just take a jog down to Home Depot, Lowe's or Tru-Value and pick up some 1/2" extruded aluminum L-stock. Even box-stock would work, anything that forms a shoulder for the filter frames to butt against.

As far as a crown for the apex of the filter "tent," I wouldn't think that it would be neccesary. In fact, since the air flow would constantly be trying to push the apex "away" from any fixed crown piece, I would worry about blow-by.

Speaking of blow-by, I should point out that when I did this on my last system the filters fit snugly in the 16" dimension (the duct was just wide enuf to squeak the filters in) and, as I mentioned, were stout enuf on their own to resist deforming. However, this is not always the case (my current system employs ducting that allows for a fairly loose fit) and in such cases extending the angled, lateral bracing the entire length of the filter would be prudent, not only to provide support, but to provide a continuous "lip" against which the filter can seal. (see pic)

..Also, how air tight to the joints between the outer duct and the angle braces need to be as well as between the angle braces and the filters?..

Assuming that your trunk duct is fairly flat-walled and not creased for rigidity, the angle stock should lay flat enuf to form a decent seal. If not, affixing the bracing in place with double-sided foam tape, then drilling and rivoting (or zip-screwing) will give you a gasket. Honestly tho, HVAC ducting is anything but airtight; a "reasonable" fit is all we're lookin' for. I used to use a business card: If I could get one of my cards into a joint, I took measures to seal it better. Again, RTV is great for sealing small leaks. NOTE: Tape should not be used inside the ducting as it can get loose and cause problems at the blower and/or heat exchanger. I know I cheat with the tape across the crown of the filters, but this is an often checked, replaceable part, not an attempt to permanently seal something within the ducting.

As far as the seal between the filter frames and the "lip" of the bracing, the velocity pressure will keep the filter mashed against it, so this is plenty of seal. Again, we're looking for a reasonable fit. A little blow-by is OK. Also, dust will tend to plug small, low-volume leaks within a short time, kinda like the way mineral deposits in tap water help to seal off any minor, low-volume leaks when plumbing.

...Am I correct that the steeper the pitch of the filters, the better it will be and the less restriction there will be due to the increased area available for air flow?..

Yes, this is correct, but as a tent arrangement using even filters of the original dimensions will effectively double your area, I would imagine that you would run into the law of diminishing returns pretty quick if you start to get too long.

...Are WEB ECO Lifetime washable filters as good as the stage loading stuff they used use?..

Ya know, I can't say. Never used 'em before. I see that the ones they sell at Lowe's have a MERV rating of 8, which is the "dust and pollen" filtration level (if I remember correctly that is) so their not just crap. Washable filters is certainly a good idea IMO. I guess you'll have to buy some and let us all know!

...where in relationship to the apex of the filter A-frame should the bottom of the new return vent be?..

Good question, and you nailed the "why." You do need a certain length of return trunk to act as a mixing plenum for the two streams to merge and work out any vortices and pressure issues prior to entering the filters. The more room the better, so rather than draw it I will simply advise to locate your new return as far upstream as possible. It's a question of efficiency; the system will work even if the new return is immediately before the filters, but the air entering them will be more spoiled than it would be if the return were located further away. Wow, you're makin' me remember stuff I haven't thought about in years! Like you said, "Thanx... I think."


Ciao!

~Snax (He Who Lurks)

 

[DonJones]

snaxforgandhi,

Okay, I think I'm ready to get down to specifics.

The horizontal run from the return stack to the furnace is 16" high so that means the lowest possible height for the base of the apex is 16" and practically speaking 17". If I just use two 16" filters the apex will be 15.20" above the base and if I go up to 20" filters then the apex will be 19.36" above the base. That means that the apex will be not less than 32" from the floor and possibly as high as 36.36" off of the floor.

In a basically open furnace room, are either of these heights likely to cause stagnation along the floor?

I could lower the base by 7" and still have the same cross sectional area in the horizontal run ans in the vertical stack by installing a 7" baffle at the upper edge of the intersection between the two runs. I'm fairly sure that the horizontal run was 16" high so that they could use a 16" X 25" vertical filter rather than an inclined or even apex type filtration system. Would I be better off to lower the base of the triangle to the 10" with the baffle and leave the lower edge of the new return vent at the 32" to 36" height to give mixing distance or to drop the lower edge of the opening the 7" too in order to get it closer to the floor to minimize stagnation along the floor?

Another way to decrease stagnation would be to mount the vent as near as practical to the floor and install a filter right behind it before the air enters the duct and then install filters upstairs just behind the vents too. What do you think of that method?

Darn just when I thought we were almost done, another issue pops up along with an entirely different approach.

Thanks again for your patience and help.

Good smoking.

 

[snaxforgandhi]

...The horizontal run from the return stack to the furnace is 16" high so that means the lowest possible height for the base of the apex is 16" and practically speaking 17". If I just use two 16" filters the apex will be 15.20" above the base and if I go up to 20" filters then the apex will be 19.36" above the base. That means that the apex will be not less than 32" from the floor and possibly as high as 36.36" off of the floor.

In a basically open furnace room, are either of these heights likely to cause stagnation along the floor?

I could lower the base by 7" and still have the same cross sectional area in the horizontal run ans in the vertical stack by installing a 7" baffle at the upper edge of the intersection between the two runs. I'm fairly sure that the horizontal run was 16" high so that they could use a 16" X 25" vertical filter rather than an inclined or even apex type filtration system. Would I be better off to lower the base of the triangle to the 10" with the baffle and leave the lower edge of the new return vent at the 32" to 36" height to give mixing distance or to drop the lower edge of the opening the 7" too in order to get it closer to the floor to minimize stagnation along the floor?

Another way to decrease stagnation would be to mount the vent as near as practical to the floor and install a filter right behind it before the air enters the duct and then install filters upstairs just behind the vents too. What do you think of that method?

Darn just when I thought we were almost done, another issue pops up along with an entirely different approach.

Thanks again for your patience and help.

Good smoking.

Hey DF,

I have read this several times and I'm afraid I cannot make heads or tails of it. When you say "base," to what do you refer? Is this the base of the furnace? (floor level?) Or do you refer to the base of the tented filters? Remember I'm flying blind without being able to actually see the ducting.

The part I did get (I think) was the question on the height of the return grille: for heating purposes the lower the grill to the floor the better. For cooling in the summer months higher is better.

Can you take a few pix of the area where you intend to cut-in for added return? That'd help me get my bearings.

Ciao!

~Snax

 

[DonJones]

Snax,

Thank you. If you were referring to "base of the apex" and the usage of base in the remainder of the first paragraph I was referring to the base of the triangle formed by the tented filters with a "baseline" drawn in connecting the bottom outside edges of the filters. In your last diagram, the base would be a straight line drawn between the 2 bottom ends of the "angle iron braces".

I'll try to get some better pictures that the ones at the start of the thread, but don't get your hopes up too much.

Thank you again.

Good smoking.

 

[DonJones]

Snax,

Here are some pictures. If you need more or something different, just explain what you need and I'll try again. In both pictures you can see a white rectangle. That is just apiece of paper that I put in for a frame of reference on the various dimensions.

The first view is standing in front of the furnace looking at it and the side view of the ducting. The short run of horizontal ducting is where the current filter stands straight up and down under the sliding cover. That section of the the ducting is 16" high by 25" from the side you are looking from to the back side of the duct and furnace. Then on the left side is the vertical stack of the cold air return that runs from the ceiling to the floor. It is 10" left to right and 25" front to rear.

The second view is taken from about 4' to 5' to the left of the position of the first photo. The furnace is in the extreme right of the photo. The side to the left of the paper is the other 25" side. I intend to cut the new opening and new filter access into the 25" side away from the furnace of the down stack.

Would I be better advised to put the vent approximately mid height of the vertical stack and rely on a fan to stir up any stagnate air on either the floor or near the ceiling depending upon whether I'm heating or cooling?

The lowest I can put the base line for the triangle formed by the tented filters would be 10" from the floor and that would involve dropping an extension down the inside of the return on the side facing the furnace which would still leave an opening where the air turns from downward to horizontal and into the furnace. That 10" high opening would be the same size as the cross section of the vertical duct --25" x 10". The bottom of the tented filters would be 10" above the bottom of the ducts and even with the bottom edge of the internal extension. This approach would only lower the bottom edge of the filters by 6" over just installing them with their bottom edge even with the top of the current horizontal duct.

If you need me to I'll try to print out your last diagram and then draw in the horizontal duct and also try to draw one showing the possible internal extension to lower the filter location.

Thank you and good smoking.

 

[snaxforgandhi]

Hi Don.

OK, I think I got it. I quickly sketched a front and side view that corresponds to my understanding of your system's geometry, so take a look and confirm or correct if need be.

Assuming I have the dimensions correct, I understand your questions to be two: How low to install double filter bracing, and at what height to cut-in for the new return grill. Yes?

First, the filters. I understand that the very, very lowest you could install your bracing would be 10" off the deck if you occluded the top 6" of the cross-section of the 16"x25" horizontal run/filter housing (resulting in a new cross-section of the horizontal run/filter housing of 10" vertically and 25" horizontally.) Yes? (See pic 3)

I assume that you arrived at the 10" high new opening in order to match the cross-section of the vertical 10"x25" return trunk? Good thinking. The calculus of the effect that hard 90* turns have on efficiency doesn't bear this out, however. You lose so much velocity pressure turning that hard 90* turn (remember that churned, spoiled air w/ vortices creates a pressure drop - Bernoulli's Law - and that translates to lowered velocity pressures downstream) that keeping the original 16" high by 25" wide dimensions of the horizontal run is preferable as this increased sectional density lowers the pressure drop coefficient. I would mount my filter braces such that the "base" of the triangle was dead even with the top of the 16" high horizontal run, and keep that big cross-section.

The next concern is, of course, where to located the new return grille. yeah? That is a concern from what I see: You want enuf "smooth" run of duct after the merging of the two air streams to effect a plenum, or a "mixing and stabilizing" zone prior to entering the filters. How much run do you need for an adequate plenum? It's hard to say exactly without having some way of measuring pressures and velocities within the return drop. (BTW, the thing I keep calling the vertical return trunk is, in the industry, called a return "drop" or "plenum." This because it consolidates all of the ducted return air into one duct, stabilizes on the way down, then enters the furnace.) So, in the absence of exact figures, we estimate. Judging by the kinds of engineering solutions regarding plenums I've encountered in the past, I would say that you'd want at least 24" of straight, uninterrupted run, 36" being better. I understand that this is probably going to locate the new return grill much higher that you had anticipated. A couple of solutions come to mind: One, drop the filter conversion. This buys you whatever portion of your vertical return drop would have been used up by filters and gets you closer to the floor. Another, more involved solution, would be to create a duct against the left side of your return drop that was open at the bottom but cut-in to the return drop higher up. (see pic 4) This is an awfully long way to ge to accomplish what it is you're after, I understand, and creates one additional 90* turn and an additional 180* turn. But It'll get you there with plenty of plenum.

Don, do one thing before you do anything else: Create whatever conditions you envision existing after the change - close off whatever return ducts you won't be using, etc - and then drill a small 1/4" hole in the vertical return drop in the approximate location of the new return grille, and check it with smoke to see if it's sucking in or blowing out. We want to be sure that we're not gonna be having to mess with any weird pressure problems before you go chopping holes in stuff. It shouldn't - all forced-air heating is positively pressurized on the output side, creating a conjugate negatively pressurized return side - but sometimes weird stuff happens that leaves even HVAC engineers scratching their heads. If smoke goes in the hole, awesome. If smoke is blown away from the hole, then the worst we've done is to drill a small hole that can be repaired in 5 seconds with a strategically placed piece of duct tape.

Ciao,

~Snax

 

[DonJones]

Snax,

Gosh you're great at converting my rambling into drawings.

Yes you are right about the 6" occlusion panel/baffle and my reasoning, but my preference was the scenario with the bottom of the new filters even with the top of the current filter housing although I wasn't sure why until you explained it.

Using that presumption, that gives a minimum top of filter height of 3' from the deck and a minimum cut-in height of 5' and preferably 6' from the deck. How would adding a room fan outside of the HVAC system but in the utility room stir up the air in the utility room enough to over come the stagnation problem?

On the other hand, if I just leave the current filter like it is and make it easier to change, Then where does that put the minimum cut-in can I just put it on the floor or do I need to use that 24" mixing distance thing?

Also, what effect, if any, does putting filters at each return vent in addition to the current one. Does that also have a similar effect to adding the tented ones since it would increase the surface area of the filters?

Thanks again for your time, consideration and mostly your patience.

Good smoking

 

[snaxforgandhi]

...How would adding a room fan outside of the HVAC system but in the utility room stir up the air in the utility room enough to over come the stagnation problem?..

I would suspect that, given the size of the return you plan to install, you will not have any issues with stalling or stagnation, particularly that close to the furnace itself.

QUESTION: Is the door to the utility room containing your furnace vented? If not, it will need to be vented the same area as the return cut-in.

...On the other hand, if I just leave the current filter like it is and make it easier to change, Then where does that put the minimum cut-in can I just put it on the floor or do I need to use that 24" mixing distance thing?..

Yeah, leaving the current filter arrangement alone would give you more leeway regarding the height of your return.

OK, here's my thinking: Since the furnace is in a utility room (that I'm assuming is not a space humans spend much time in) if we close the door, the door vent location becomes paramount regarding efficient re-uptake of return air. (See pic) In this instance, you can cut-in up high on the return drop to garner as much plenum space as we can, but be pulling only cool air from the area outside the utility room.

...What effect, if any, does putting filters at each return vent in addition to the current one. Does that also have a similar effect to adding the tented ones since it would increase the surface area of the filters?..

No, the effect is actually opposite that of a tented arrangement. If we filter each return vent in addition to the current filter, then we have arranged them serially which creates cumulative resistance.

Have a Very Merry Christmas Don, and only the Best Fortune in the New Year!

~Snax

 

[DonJones]

Snax,

There is no door on the utility room, just an open archway about 6' wide and 7' tall. Currently there is NO return venting from the down stairs bedroom. Wouldn't I need to provide a vent for it, maybe by venting the door like you showed for the utility room door?

The other downstairs room is the grow area and I'm not worried about stagnation there because I've got a 20" box fan exhausting from the grow room and a 8" x 24" intake vent from near the floor under the stairway, so I should have enough mixing in that area..

How does this effect your thinking?

What about removing the current filter putting filters on each return-would that let me put the cut-in down low without creating stagnation problems?

Thank you. We wish you and yours a MERRY CHRISTMAS and a HAPPY PROSPEROUS NEW YEAR!

Good smoking

 

[home grow]

sorry I did not read the whole thread, but have you tried turning all upstairs dampers half way closed and opening all down stairs damper all the way open?

 

[DonJones]

home grow,

I've tried everything I could think of. Basically what I think I'm dealing with is trying to force cooler heavier air up the stairs to the returns which obviously isn't very effective.

Thank you for the input.

 

[snaxforgandhi]

Hola DJ! Hope you and yours had a Very Merry Christmas!

...There is no door on the utility room, just an open archway about 6' wide and 7' tall. Currently there is NO return venting from the down stairs bedroom. Wouldn't I need to provide a vent for it, maybe by venting the door like you showed for the utility room door?..

Yes, that bedroom would certainly benefit from any augmentation that precipitated easier pressure regulation. Since there are no returns downstairs, venting the b/room door down there essentially turns the hallway (or whatever spaces the return air passes through on its way back the the utility room) into a plenum.

...The other downstairs room is the grow area and I'm not worried about stagnation there because I've got a 20" box fan exhausting from the grow room and a 8" x 24" intake vent from near the floor under the stairway, so I should have enough mixing in that area..

How does this effect your thinking?...

Am I assuming correctly that when you say you have a 20" box fan exhausting, and a corollary intake vent, that these are both to-and-from outside fresh air respectively? If this is so then you have a self-regulated subsystem in your grow room, and you'd want that system to be as isolated from the rest of the house as possible to avoid weird pressure issues. I'd just make the door seal fairly airtight, no need to go nuts.

What about removing the current filter putting filters on each return-would that let me put the cut-in down low without creating stagnation problems?..

We talked about this a couple posts back. I believe that filtering at the source return vents would create excessive resistance. I wouldn't worry too much about stalling or stagnation at or near the actual furnace, here's why: As far as the system is concerned, return location and capacity only matter insofar as they eleviate pressure dif problems. The system doesn't care about stalled or stagnant pockets as long as they create no pressure related circulatory issues, but the human in residence does care 'cuz they can create cold/hotspots. But as long as these anomalies occur only in areas not associated with human occupation (like utility closets) then there's no worries.

It's now 11:52 on 12/31 and I must go find my Maker's Mark, I know I had it a minute a go. Better hurry, I've only got 8 minutes left!

~Snax (He Who Can't Find His Drinky-Winky!)

 

[DonJones]

Thank you. Happy New Year!

Great smoking to everyone!