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Old 05-16-2009, 11:35 AM   #1
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Ducting for heat - registers high or low?


I'm beginning to work out the ductwork for a new furnace installation (added 1000 feet still under construction) with no existing ducting.
The house is a long narrow 2 story with a 500 sq ft lower room downstairs. The furnace will be a gas fired up-draft located centrally on the 1st floor. The ducts will run through the attic/trusses but I also need to get some heat downstairs as well.
The downstairs is built from ICF walls and the only way I can have registers at the floor would be to make a false wall. If I put the registers in the cieling it would be much easier but I think that it won't be very efficient (due to heat rise).

Any ideas? Also, has anyone used those online duct engineering services? Apparently you send them a sketch of your floorplan showing rooms and joist direction/spacing and they do a take-off for you.

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Old 05-16-2009, 12:18 PM   #2
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Ducting for heat - registers high or low?


Select supply registers with a downward throw.
And put your returns low.

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Old 05-16-2009, 12:37 PM   #3
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Ducting for heat - registers high or low?


Quote:
Originally Posted by beenthere View Post
Select supply registers with a downward throw.
And put your returns low.
Beenthere, thanks for responding so quickly. You mention that I should put the returns low. This defeats the concept of not running duct down the ICF walls. If I could put the returns low, I'd simply put the registers low and move on. Am I not understanding something?

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Old 05-16-2009, 12:46 PM   #4
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Ducting for heat - registers high or low?


LOL... No, just me being senile.

Your returns can be high.

Make sure the supplies throw the air down to the floor.
It will mix the lower cooler air with the warm air, and help to keep your feet from being cold.
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Old 05-16-2009, 02:17 PM   #5
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Ducting for heat - registers high or low?


high supply and returns are common on commercial installations where the hvac system is often above a lay-in ceiling. As beenthere states, the registers used plus the proximity to the returns is going to make the difference for you.
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Old 05-16-2009, 02:29 PM   #6
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Ducting for heat - registers high or low?


I get it - that was just me being too serious

I'll probably have only one return - in the short hallway right infront of the furnace. The location is pretty central to the main floor floorplan and is probably all I need.
The downstairs will be the toughest to heat because of all the mass in the ICF walls and I fear most of it is just going to go right up the open stairwell.
Maybe putting the "downflow" register as far from the stairs is the best I can hope for.

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Old 05-16-2009, 05:18 PM   #7
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Ducting for heat - registers high or low?


you need returns in each room except a bathroom and the kitchen. Lack of a return will cause the room to pressurize if the door is closed and will not heat or cool properly due to the lack of the air being able to flow through the room.

You don't put one in the bathroom because you do not want to circulate the stink throughout the house. The same for the kitchen. Well, that is if your cooking stinks. You do not want to circulate the smoke and oils associated with cooking.
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Old 05-16-2009, 05:40 PM   #8
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Ducting for heat - registers high or low?


I have read that if the interior doors are about 1 1/2 to 2" from the floor that this is enough to transfer return air for most bedrooms - which are the only rooms I have with doors other than bathrooms.

Is this a poor way of doing it?

Last edited by Jim W; 05-16-2009 at 05:50 PM.
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Old 05-16-2009, 07:34 PM   #9
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Ducting for heat - registers high or low?


It works ok.

Many houses are done like that.

While individual returns are better. Under cut doors are ok.
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Old 05-16-2009, 08:39 PM   #10
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Ducting for heat - registers high or low?


Thanks Beenthere,
Everyone here has been very helpful

What is your take on a "duct design Service"
I have a autocad floorplan and can send a PDF file to them
for around 400 bucks they do a take-off and give me a materials list and drawing. Sounds kinda spendy

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Old 05-16-2009, 10:13 PM   #11
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Ducting for heat - registers high or low?


If you have teh full plan.
A service is usefull.
They are expensive. but can be worth it. When you consider the headaches they can save.
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Old 05-16-2009, 10:23 PM   #12
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Ducting for heat - registers high or low?


Thanks again
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