Worth adding a cold-air return?

[DeanBrown3D]

Hello all,

I have a wood furnace in my basement with central forced air, and
right now (all winter so far) I have been leaving the basement door
open so that the cold air return is sucked down the stairs.


I'm considering connecting up the returns to the furnace so as to make
a closed system, and I wanted to know if this makes much of a
difference in fuel usage and/or house temperatures. Right now, the
furnace has a struggle with a 50-degree difference outside vs. inside,
so if its 20F outside, I can almost not reach 70F inside.


Any experiences welcomed here.


Thanks


DeanB

 

[begreen]

Short anwer, yes. Unless things have changed from the initial posting, it looks like the return was never connected on the wood furnace. Is that correct? If so, it's drawing it's return air from the basement. Normally the wood furnace return air is ducted to the main return. You'll also need to add a dampering system to avoid looping through the main warm air furnace.

What does the Charmaster manual show for connecting to an exisiting system? I can't find a manual online. From a previous thread where we discussed this, I posted some diagrams and if I remember right, Yukon covered it well for their furnaces.

Here't the thread:
https://www.hearth.com/talk/threads/4945/

 

[DeanBrown3D]

The return is not connected. There is a 16x20" rectangle on the side of the furnace that is supposed to join up with the return ducting that already goes into the electric furnace. However, I added a blanking plate to the electric so it can't blow through it. Electric is turned off complately now.

Basically all I have to do is drop down a large 20" duct pipe, from the return ducting to the furnace. I just wanted to know if this would make a BIG difference or just a minor one. The plus side is that my basement is very warm, not that I really care that much!

I can take a pic tonight if this is not enough.

Dean

 

[begreen]

No pics needed, your first install pics show it pretty well. A properly sized and connected return duct will increase efficiency a bit. You'll be able to leave the basement door closed too. How well it will work depends on how much the return air is currently being cooled down by the basement. Are the basement walls insulated? Insulating the return duct will also help.

Are the existing supply and return ducts insulated on the interior of the ductwork?

orig. pics:
https://www.hearth.com/talk/threads/4674/

 

[DeanBrown3D]

Wow thanks for finding that pic!

Its a 70x25x9' high basement, not insulated. There are 4 windows, 3 with plastic sheets covering them to stop the air gaps. Rest of house is 1.5 times that area.

The supply and return are both insulated inside, except for the little piece attached directly onto the wood furnace, which I will insulated at some point.

Are we talking about 5% fuel savings, 20%, 50%?

 

[begreen]

Hard to say. Is the basement ceiling insulated? If not, then there is some heat gain through the floor. But that is a big space to heat if unintentional. I would lean towards the 20% figure.

FWIW, I'd hold off insulating the supply coming off the wood furnace in favor of connecting an insulated return pipe.

 

[DeanBrown3D]

Ok sounds good. The floor is insulated, its actually a pretty decent house compared to my last one. 20% would be good too!

Thanks

Dean

 

[Roospike]

DO IT

I think is would complete the system and also you wouldn't be drawing cold air from the basement ( ie: cold floors , cold walls , ect.. )

As i understand its the upper part of the house you are trying to heat so i think adding the return air is going to be nothing but +'s

 

[laynes69]

Our furnace is installed a little different (In Series), but when I did this which uses the whole home ducting both supply and return what a difference. Does your furnace have a control limit on it? I found that if you change these setting for what you need you can get better heat. We have no problems in 20 degree weather, but when it was down to -10 it was hard to keep 70 but we did it. Without a doubt tie into that cold air. For us it made even heat, less dust because of the air in the living space not the basement, and stopped drawing combustion air from the furnace. That furnace should do better than 70 in 20 degree weather, but insulation and how well the house is sealed will make the difference everytime. Hows it do on wood consumption?

 

[begreen]

You should be able to quantify the change. Measure the temp coming out of one of the warm air registers now. I'm guessing it will be about 115 degrees depending on how far from the furnace the take off is. Then add the insulated return duct, shut the basement door and let her run for awhile. Measure the temp at the same location as the previous reading. I wouldn't be surprised if you saw a +5 degree or better rise in temp.

 

[reaperman]

I also have a wood furnace that isnt connected to the cold air return. I plan on getting it connected after the heating season is over. The guy who installed the HVAC system didnt connect it. Apparently not a woodstove guy. But my furnace is close to the stairway where there is no door. Anyway, I was talking to the manufacturer and mention this to him. He said, all I have to do is put 3 register grates, 4" x 12", and mount them in the cold air return line, in the basement about 10 feet apart, near the wood furnace. And this will draw air from upstairs, and there would be no further need to do anything else. I havent done this, and dont plan on it. I will have it connected the normal way. But I will say there is one register grate in my cold air return in about the center of the basement, 6x12. I'm not sure of its purpose, but I can feel air moving from it when the furnace blower is running.

It seems odd you cant pull more heat from that monster furnace. I have no trouble getting 80 degrees at -20 temps with my furnace. But my house is brand new, and is very well insulated. Good luck

 

[begreen]

Reaperman, your wooodstove guy is trying to save you money, but that is not a substitution for direct connecting the return. It still makes the room the duct. Good for you to sticking with the right way to hook it up. It sounds like your basement was designed to be heated. Is there also a supply register(s) blowing into the basement space somewhere?

Good to hear you have a well insulated space. That really helps. How many sq ft are you heating? What is the furnace?

 

[reaperman]

BeGreen, I have 4 supply registers in the basement, two in the "living room"(not finished), one in the bedroom and one in the bathroom. They are 8" circular type, look kind of like a bee-hive. I wanted my basement as open a possible. I have one large room downstairs, 20'x40', and the mech room, bathroom, and semi-bedroom, share a 12'x40' space. My total home is 32'x40', upstairs and basement (walkout). So 1,280 sqft on each level. Not big, but its all the wife and I need. One benefit is my location with southern exposure and very heavily wooded to block that nasty NW wind. My furnace is a firechief model 500.

 

[begreen]

OK, your situation is quite different from Dean's. This is a heated living space with a smaller footprint. My guess is that your basement walls are also well insulated, is that correct? In your case you really want a return air intake in the basement.

The way it's been described, Dean's basement sounds more like a utility space that would be fine if it were at 50-55 degrees.