Am I Starving My House for Air??

btrowe1 · Post by **btrowe1** » Thu. Jan. 03, 2013 6:17 pm

I am thinking I need more air flow to the house. I've researched the subject but there's so much mumbo jumbo talk (I know its important but way too technical)) that its hard to understand. I have a forced air coal furnce, I have a 10" return ducted in, I have an 8" distributing out. The house is warm, but I just think I'm on the small side for distribution and that I should add another 8" line out giving me 16". While I'm pushing air I think that possibly I'm building up a bit of pressure due to the reduced size of my output duct.
Here in Upstae Ny it was -18 this am and the house was oh so toasty.. So I know it works, As is all coal burning ( I think it's a hobby) one is always tinkering with something to achieve the best end result, I've been doing this for many a year and always find something new each year, thanks in advance for any and all answers. And a happy new Year to you all.

Post by **Lightning** » Thu. Jan. 03, 2013 7:06 pm

Starving the house for air?? I would say no since the air going back into the house from the furnace to the heat registers will be the same amount of air that went to the furnace thru the cold air return, regardless of their sizes... BUT if you want more air flow in general, add more heat runs and more cold return..

Hope this helped..

plumb-r · Post by **plumb-r** » Thu. Jan. 03, 2013 7:57 pm

To answer your question one must know how many cfm your fan is able to push. Certain size ducts move certain amounts of air. Help us help you with more information.

steamup · Post by **steamup** » Fri. Jan. 04, 2013 7:55 am

Hook up and configuration is the key. In my opinion, manufacturers undersize their duct connections. A 10" round doens't move much air if it is long. It must be kept very short and use a strong enough fan.

A 10" inlet and outlet as a short injection loop to an existing furnace may work with the right fan but may be noisy. A single 10" return from a register will probably not make for very efficient operation.

8" diameter is way too small for supply for one furnace. Two 8" diameters doesn't make a 16" equivelant. It goes by duct area, not diameter.

In order to comment more, we would need to know a little more detail about your system.

Post by **Lightning** » Fri. Jan. 04, 2013 8:25 am

Good point Steamup.. 2 - 8 inch round should be double the volume as 1 where a 16 inch round would give you 4 times the volume of 1 - 8 inch.. hahaha

btrowe1 · Post by **btrowe1** » Fri. Jan. 04, 2013 7:34 pm

Update::: Added the 2nd 8" line today, Much different than the single one. more air flow into all rooms, blower motor is noticibly quieter, the return is also quieter, no more excess air is being pushed throught out of every joint on the distribution hookup (where the top of stove hooks to my duct work). I had a flate sheet metal plate made and a single " hole cut into it.

My return is a very short run as my stove is directly below my living room which is the center of the house,The old furncae was upstairs and just used the living room as its return, I'm basically doing the same only with a 10" line.

The furncae is a typical alaska 140 with a 1550 blower motor,

Yes the 16 inch duct would be nice but I only have a single 12" square crossing my basement and 2 12" runs coming from it running the length.

Seems to be working as I have been able to drop my hi feed rate back 2 settings and the house is holding 68 degrees. don"t laugh we like it a bit cooler than the 70+++ we use to get from the wood stove. I remember nights when it was below 0 and we had the windows and doors open to cool off.

I'll take a few pictures and down;oad them later and send out tomorrow..

Rigar · Post by **Rigar** » Sat. Jan. 05, 2013 9:44 am

Btrowe1
... you're not starving your house...as much as youre "starving" your blower.
every house is different... and I don't know the length of your ducts... floor plan etc....
8" round duct- 160 cfm
10" round duct - 400 cfm
12 x12" sq. duct-700 cfm
these are a good "rule of thumb" to start with
as long as your supplies arent excessively long and with minimal turns (elbows)
As you can see your blower can handle MUCH more ductwork
just by doubling your heat supplies you have noticed a difference in noise alone....that is due to lower air velocities within the ductwork...and also slightly lower rpms on the blower itself...due to it moving more air (work/resistance)
...remember ...if you add more hot air supply ducts...also try to increase the cold air too (if possible) .too little on either side will create an inefficient system