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Old 01-09-2009, 02:23 PM   #46
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Good deal. I'll need to see how well I can fit this in my space, I am sure I can come up with something.

Most of the ductwork will be in conditioned space, except for the couple of lines I run up in the attic, so that's good.

What size grille would you suggest for the 14's? For the 8's?

Thanks!

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Old 01-09-2009, 03:12 PM   #47
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I've poked around a lot on the internet and can't seem to find a stackhead box that accepts 14" duct, seems to max out at 8". Any thoughts?
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Old 02-07-2009, 10:46 PM   #48
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Ok, so after a very long hiatus, I'm back. integlikewhoam, I certainly hope you see this!I've done a bit of investigative work and it looks like I'll need to change course just a little bit based on some new measurements. Last we talked, the plan was to run 2 14" rectangular ducts to handle return air from from main level. Unfortunately, I have a plumbing stack in the way, so it just won't work. That said, I think I have a plan. Here is what I am thinking. I'd really appreciate your evaluation.

1) As previously discussed, I'll close up the current 8x12 rectangular duct so that it only services the second floor of the home. = 400 CFM

2) I will add either 1 8" round or 2 6" round returns to the basement. = 250 CFM

3) I will run a 21" x 10" rectangular duct to service the first floor of the home. = 1000 CFM

By making these changes it looks like I will go from 400 CFM of return to 1650 CFM of return, so big, big change.

Now, the problem is, I am still uncertain as to how to pull this all off. I've taken a couple of photos of the current setup in hopes it might help. To put it all in perspective, our air handler uses a 16x20x1 filter. Looking at the wider angle photo, working from the bottom up you have the plenum, the next run of ductwork from there is 20x8 and then it reduces down to 12x8.

So, is my proposal even possible based on the setup? Is the 20x8 duct part of the plenum? If so, can I tie right into that? Or, do I need to start by finding a new plenum? Also, just so I can figure out (tell my wife) how this is going to look, what size grills will be required for the various elements?

Thanks!
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Old 02-08-2009, 09:06 AM   #49
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Your getting some good advise.

You may also want to check a few things before you do your duct alterations though.
First, check the temp of the air at the supply closest to the furnace, or the one that blows out the most air. See how hot it is, compared to the return air temp.

We can tell roughly how much air your furnace is currently moving by its temp rise.

You have a 100,000BTU input furnace with a 5 ton drive, matched to a 3 ton A/C.

You need to be able to move enough air for the furnace in heating. But, still be able to lower that to 1200 CFM for your A/C in summer, other wise, if you move too much air in cooling. You will have high humidity problems.

Running individual returns to your upstairs rooms is a good idea.

Abandoning the current first floor return, and making one some where else on the first floor is a great idea.
Making it that you can restrict that first floor return in summer will help in cooling the second floor in the summer.

Adding a return to the basement, WELL, depends if the furnace room has outside combustion air or not. If outside, good, if not, bad idea.

A study done in Florida. To prove the pit falls of oversizing went bad, when they forgot 1 little detail.

In these houses, they removed system that were oversized by ˝ to 1˝ tons.
They did load calcs, and installed the proper size.
Unfortunately, they did not install any way to restrict the return air. So they were not able to slow the air flow down for the new smaller A/Cs.
Few of the houses saved any money. And there were complaints that the houses were now too humid. Causing some to lower their thermostats a couple degrees lower then with the oversized units. So they used more electric with the proper size.

Point of telling you that. Is that if you increase return, and don't allow a way to decrease the air volume for the summer, you will make your house more humid, and use more electric then last year.
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Old 02-08-2009, 07:14 PM   #50
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Wow, thanks so much for all the advice. I certainly couldn't take on a project like this without it.

I can figure out to measure the temp at the supply, but how do I go about measuring the temp at the return?

So, regardless of heat or cooling, the 12x8 return air duct is significantly undersized, right? Am I about on point with my proposal, so far as obtaining 1600 CFM of return?

What do you suggest for how to limit the return on the main floor? A louvered grill or do they make a damper or something I can install down in the basement?

As for installing a return air vent in the basement itself, it is actually living space, heated and cooled. I do not believe that there is any outside combustion air, but the door to the utility closet is louvered. There are actually three rooms in the basement. What do you think?

So, Now, the problem is, I am still uncertain as to how to pull this all off. I've taken a couple of photos of the current setup in hopes it might help. To put it all in perspective, our air handler uses a 16x20x1 filter. Looking at the wider angle photo, working from the bottom up you have the plenum, the next run of ductwork from there is 20x8 and then it reduces down to 12x8.

So, do you think my proposal from my last post is even possible based on the setup? Is the 20x8 duct part of the plenum? If so, can I tie right into that? Or, do I need to start by finding a new plenum? Also, just so I can figure out (tell my wife) how this is going to look, what size grills will be required for the various elements?

Thanks so much!
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Old 02-09-2009, 10:23 PM   #51
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Bump...
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Old 02-10-2009, 07:10 AM   #52
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Even your 8x20 is too small.

You don’t really have a return plenum.
You have a return drop with a ell. And no vanes.

Your drop should be 12x22 or 10x28.

A sidewall return grille (non filtered) for the first floor should have roughly 380 sq in of free area, making it about a 20x20 to a 20x24 grille face.
Depends on what type of return you have installed on the main floor. Sidewall or floor.
And on how its tapped into the system.

If by a duct into the drop, then a damper can be installed in the duct that runs between the grille and duct.

Since the basement air is used for combustion. You MUST be careful not to install a return that could put the room into a negative pressure, and draw flue gasses into the basement and harm or kill someone.
You’d be surprised how much air a furnace needs for combustion.
Since basements tend to cool quickly in the summer, a small return, may be ok. But many people shut the supplies in the summer, and if the duct system, and return grilles to the other floors in not enough, it will put the basement into a negative pressure.

As for measuring the return temp. Place a thermometer at or in the return duct on your first floor.
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Old 02-10-2009, 10:50 AM   #53
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Thanks so much. Looks like we're getting somewhere. This project seems fascinating, but I am still a bit intimidated. I've got a fair amount of DIY experience, but not much experience with HVAC, so it's great to learn. Thanks for your patience and guidance.

So, a couple of follow-on questions...

1) If I don't have a plenum, do I need a plenum? Or am I OK by increasing the return air drop to the sizes you indicated?
2) In order to increase the return air drop do I need to change out the ell?
3) What I am confused about is how to connect a 12x22 or 10x28 drop to the air handler. Do I need to replace the ell? Do I need to replace the filter frame? Can I use something like this? http://www.audubonsupply.com/browse.cfm/2,154.html
4) The main level will utilize a sidewall grill. Unfortunately due to space restrictions, I am planning on using something like this, http://www.audubonsupply.com/browse.cfm/4,1122.html to cap the 20x10 run to the main level. Would this work?

I will check the temperature differential this evening and report back.

Any thoughts? Is this work remotely feasible? I am just hoping I can fit it all into my little utility closet. Ugg! It would be nice if people did things the right way the first time around!
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Old 02-10-2009, 01:22 PM   #54
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The link to the return packages, have the ell for connecting to your furnace.

I thnk those packages have teh filter slot in them, but I'm not sure.

The second link, you can use that ell.

Where there is a will, there is a way.
Do you know anybody named Will? LOL...

Measure how much room you have in your furnace room, before proceeding.
Easier to change a plan in the beginning, then in the middle.
You may need to have a sheetmetal shop make a fitting for you, depending on the amount of install room you have.
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Old 02-10-2009, 02:15 PM   #55
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Couldn't agree with you more, owning a home has taught me that the only limit is my patience, really. Thanks for all the help. I am just hoping your patience doesn't wear out!

I have been looking through the materials related to the furnace and am a little confused. You can find the specs for my air handler here, http://www.allreds.net/WS2/docs/rhe/80ps_specs.pdf. There's some contradictory information in the document, or at least based on my understanding. On page 3 it indicates that the standard filter for my unit is 19.25x25. That said, the diagrams on page for seem to state that the right/left side return air cutout is only 23x15. What do you make of this?

The kits seems to include just about everything I'd need to make this work,
but not so sure about the sizes. From what you said earlier, the 20x10 with 20x16 filter is too small, right? The next size up seems to be 25x10, which is too big for my air handler. Any thoughts?

I think I need to start here, figure out how much room I need and then go from there.

Thanks!
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Old 02-10-2009, 08:17 PM   #56
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Also, just a thought. In reviewing the information on the air handler, it looks as though it runs at a higher CFM when cooling. Based on your previous indication that we need to reduce CFMs during the cooling cycle, would it be possible to change this setting somehow? ** This is getting way ahead of myself, I know, but wanted to write it while thinking of it**
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Old 02-10-2009, 10:29 PM   #57
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The filter the manufacturer suggest is always smaller then the opening.

The 10x25 would be fine for your furnace.

The blower speed for cooling can be slowed down by using the blower speed taps.
Just have to selelct the correct one for your A/C. Will probably be the low speed tap.
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Old 02-10-2009, 10:40 PM   #58
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Beenthere, I feel guilty not knowing your name, you've been so helpful. Mine is Adam.

Thank you, thank you, thank you for looking through all those specs.

Excellent! So, if I use the 10x25, even thought it is a bit smaller than what you suggested (22x12 or 28x10) I should be fine? Will this allow me to move 1600 CFM or so? I suppose I can just enlarge the hole in the air handler where it attaches by a few inches to get it to fit (currently I think it is 20x16), right? Do I just use a hacksaw?

With this setup, I can tie in the current 12x8 duct running up to the attic, as well as the 20x10 I am proposing to serve the main level of the home, right? Can I just tie straight into the 25x10 drop? Just cut an appropriately sized hole in the side? That simple?

Returning to the issue of the basement, the house is really not the least bit airtight, it is a 75 year old home. Does that help? I'd plan on installing the basement return in different room from where the utility closet is housed. Does that work?

Last edited by stubits; 02-11-2009 at 04:47 PM.
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Old 02-12-2009, 07:49 AM   #59
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Old 02-12-2009, 03:26 PM   #60
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For some reason. i don't get email notification from this site. Could be my ISP.

My name is Jim.

The 10 x 25 will be ok for 1600CFM, it will run a slightly higher static pressure, but with it being short, not very high.

Both the duct to the attic, and the new one for the first floor can be cut into the 10 x 25.
It takes a little practice to cut them in smoothly and correctly.

You may want to install the 10 x 20 first, with the duct from the attic tapping into it, right above where the 10 x 20 sits over the 10 x 25.

The hole in the furnace, can be enlarged by either tin snips, shears, sawzall, jigsaw, or, the hard way, hack saw.

I prefer, electric shears.

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