Proper Duct Work ???

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Bity454
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Post Thu. Jan. 17, 2013 8:49 am

Question 1) If you have 2 six inch ducts into room, should you have 2 six inch or equivalent out ?

2) Should cold air returns be by the ceiling ?

3) Should heat ducts be under outside windows, or on interior walls ?

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Berlin
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Post Thu. Jan. 17, 2013 9:11 am

heat ducts - exterior walls/windows. Return ducts interior walls, low, when in a heat climate (such as ohio). returns need to be as big as supply; less and you typically get noise and create positive pressure in room which tends to push conditioned air out of the housing envelope.
Burning western Pennsylvania Bituminous in WNY using model 77 stoker furnace. BITUMINOUS equiptment: 2 hand fired stoves of my own design, Many Combustioneer Model 77 stokers, stokermatic furnace, Many Will-Burt stokers, & and Two Iron firemen.

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Post Thu. Jan. 17, 2013 9:13 am

Bity454 wrote:Question 1) If you have 2 six inch ducts into room, should you have 2 six inch or equivalent out ?

2) Should cold air returns be by the ceiling ?

3) Should heat ducts be under outside windows, or on interior walls ?
1 my returns are approx 50% larger than heat ducts. 2. Cold air sinks because it is heavier, there for at floor level. 3. heat ducts by the windows are ideal to compensate for any drafts that get by the windows. My returns are centrally located in my ranch and my heat ducts are technically not on the outside walls but as close as possible on interior dividing walls because my brick house built in 1955 by italian imigrants used cement block for the load baring along the perimeter, with furring strips and then double layers of sheet rock, and the sheet rock was probably the first generation because the sheets are smaller than 4x8'
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CoaLen
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Post Thu. Jan. 17, 2013 9:22 am

My DIY opinion:
1) Cold air return must be equal to heat vent as a minimum. Slightly bigger is better.
2) Should be on the floor, opposite side of the room from the heat vents.
3) Should be under the windows (outside wall).

There are some guides on the internet for installing ductwork.
Here's one: http://www.alpinehomeair.com/related/Ductwork.pdf

It's as much an art as it is a science.
“The trouble with quotes on the Internet is you never know if they are genuine.” —Abraham Lincoln


Rigar
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Post Thu. Jan. 17, 2013 10:22 am

All of the above...( in a way )....

for maximum comfort and efficiency.. supply air should enter a room as close to an outside wall as possible ( under windows are ideal)

cold air returns should be located opposite of the supply... which typically places them on an interior wall..( and yes they should be at floor level)

your cold air return duct size does not have to be larger... nor is it recommended.
every system is different... however.. a larger capacity return has the POTENTIAL ( if the air handler allows it) to create a slightly NEGATIVE pressure condition with in the room itself ( all things being equal)... and will actually encourage outside air infiltration. (cold drafts)
if you know your systems capability (cfm ,velocity, etc) and are confident that the room requires two (2) six inch supplys (a fairly large room) I would suggest one 8 inch return air duct- if it was feasible- but two (2) 6 inch returns would be fine
....'Rigar

CoaLen
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Post Thu. Jan. 17, 2013 11:51 am

Rigar:
your cold air return duct size does not have to be larger... nor is it recommended.
every system is different... however.. a larger capacity return has the POTENTIAL ( if the air handler allows it) to create a slightly NEGATIVE pressure condition with in the room itself ( all things being equal)... and will actually encourage outside air infiltration. (cold drafts)
That's not right. Slightly larger return air area will reduce air flow noise and encourage/draw hot air flow into a room. Cold air infiltration of any consequence is addressed as a separate issue, such as sealing up windows and doors. Return air vents should be slightly larger or at least the same size as the heat vents.
“The trouble with quotes on the Internet is you never know if they are genuine.” —Abraham Lincoln

Rigar
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Post Thu. Jan. 17, 2013 12:19 pm

CoaLen wrote:
Rigar:
your cold air return duct size does not have to be larger... nor is it recommended.
every system is different... however.. a larger capacity return has the POTENTIAL ( if the air handler allows it) to create a slightly NEGATIVE pressure condition with in the room itself ( all things being equal)... and will actually encourage outside air infiltration. (cold drafts)
That's not right. Slightly larger return air area will reduce air flow noise and encourage/draw hot air flow into a room. Cold air infiltration of any consequence is addressed as a separate issue, such as sealing up windows and doors. Return air vents should be slightly larger or at least the same size as the heat vents.
...I guess we will just have to agree to disagree my friend.
....'Rigar

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steamup
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Post Thu. Jan. 17, 2013 1:07 pm

Let's look at the physics.

Air has mass. Air handlers do not create mass, only move mass. Fans push more efficiently than they pull. It is better to have less duct friction loss on the return of a fan.

With that said, what goes into the room must go back out. Therefor the return must be at least equal if not slightly larger than the supply. If the room goes negative, it would be because the air from the room next to it is trying to get to the other room's return. Air simply will take the path of least resistance.

Air will only be sucked into a house if there is a place air is being leaked or forced out of a house. The pressure differential with a furnace system is in relation to its self and not the outside. Two different issues.

Cold air is more dense than warm air and therefor drops. Cold air returns are best on the floors for heating systems.

In northern climates, we place our duct supply on the outside walls for best comfort. Near or under windows is best as that is where drafts or heat loss is most likely to occur.
Steamup

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Rigar
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Location: central new york (syracuse area)

Post Thu. Jan. 17, 2013 2:38 pm

Steamup...your points are all valid
.. however... my recommendations to the poster were based on previous post he has made before.
I believe it is an old farmhouse (1830 c.) ?
and he has admitted there is as much wind inside as outside! ...( now I'm sure he is exaggerating! :D )

what we don't know is the capabilities of his furnace and EXISTING ductwork.
I would never miss guide anybody intentionally... my logic was in HIS situation.. larger return air duct may have no benefit... but yes equal to would be fine
it is my understanding that he is utilizing more than 1 Coal Fired appliance... with 1 being a power vented unit I believe... with this said... the stove and or furnaces alone are creating negative pressure in the house already.. now turn on a bathroom exhaust fan... and the clothes dryer... increasing the negativity within the home even more. These all add up... and play a role.... and therefore should be considered( in my opinion).. but the bottom line is... everyhome is different... and what works for one- may not work for another.
ultimately.. I hope Bity454 takes some knowledge from ALL of the posters here.
..... be well and stay warm everyone.
....'Rigar

Bity454
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Post Thu. Jan. 17, 2013 4:42 pm

No not exaggerating to much :cry2: thanks for all the replies, all have very good points. Currently using the basement door as a cold air return, but contemplating a re-do of the duct work, with proper cold air returns. The little smaller cold air return idea sounds pretty plausible for my drafty condition.

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steamup
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Post Mon. Jan. 21, 2013 8:25 am

Rigar wrote:Steamup...your points are all valid
.. however... my recommendations to the poster were based on previous post he has made before.
I believe it is an old farmhouse (1830 c.) ?
and he has admitted there is as much wind inside as outside! ...( now I'm sure he is exaggerating! :D )

what we don't know is the capabilities of his furnace and EXISTING ductwork.
I would never miss guide anybody intentionally... my logic was in HIS situation.. larger return air duct may have no benefit... but yes equal to would be fine
it is my understanding that he is utilizing more than 1 Coal Fired appliance... with 1 being a power vented unit I believe... with this said... the stove and or furnaces alone are creating negative pressure in the house already.. now turn on a bathroom exhaust fan... and the clothes dryer... increasing the negativity within the home even more. These all add up... and play a role.... and therefore should be considered( in my opinion).. but the bottom line is... everyhome is different... and what works for one- may not work for another.
ultimately.. I hope Bity454 takes some knowledge from ALL of the posters here.
..... be well and stay warm everyone.
I think we are saying the same thing.

The cold air return size will not effect the relationship between the house pressurization in relationship to the outdoors. Interior use of air for exhaust, combustion, etc. creates a negative pressure within the house. Air will enter the house through the easiest path(s). --- Just trying to separate the issues here.

Reducing the cold air return ductwork size will have no bearing on this problem. Yes, equal size should be fine providing it is properly size. If the existing supply ductwork is noisy/drafty, it may be too small or there isn't enough supply registers to distribute the air. I am not sure what the exact problem is but using the basement door for a return and the basment as a return air plenum is not good design.
Steamup

"You must learn from the mistakes of others. You can't possibly live long enough to make them all yourself."
Sam Levenson
"Make everything as simple as possible, but not simpler."
Albert Einstein

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