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Old 12-23-2010, 04:52 AM   #1
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Heating Unfinished Basement


I live in a 4-level sidesplit and the lower basement level where the furnace is located is completely unfinished (concrete floor and walls exposed, leaky rim-joists and all). It's almost completely below grade except for the top foot and is about 500 - 550 sqft.

There are two ducts down there that are currently turned off. Can i open these up and heat this space without getting into problems with condensation, etc? I'm thinking that it will make the floor of my kitchen, dining, and living rooms more comfortable.

The thermostat is located in the diningroom above this unheated space.


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Old 12-23-2010, 05:45 AM   #2
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Heating Unfinished Basement


Might want to tighten up the basement first. If it leaks too much, you'll see a big increase in your heating bill.

Is there also a return in the basement. If not, you could end up forcing heated air to go out through the other that leak (after you seal up some of the leaks). Which will cause the other levels to go into a negative pressure, and draw in cold air from the outside.

So seal some of those leaks first(this will help the basement stay warmer alone). Then install a return if one is not already installed in the basement.

Also, make sure that there is enough combustion air in the basement for your furnace if it uses basement air for combustion air.

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Old 12-23-2010, 08:11 AM   #3
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Heating Unfinished Basement


Thanks for the reply. There is no return in the basement.

More importantly though I didn't think of the fact whatever the furnace blows out it has to suck in...if some of the heated air is lost from the leaky basement it would have to be made up by being sucked into the house from somewhere else (somewhere cold probably).

I feel silly for not thinking of that myself

I'll have to seal up the rim joist areas first and see how cold it is down there then before considering making it into a heated zone. How do I know if I have enough combustion air available?
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Old 12-23-2010, 10:58 AM   #4
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Heating Unfinished Basement


I have two vents in my basement, and the temp stays around 60 degrees. R-13 Fiberglass batts in the Rim joists, Foam boards in the windows down there, due to huge air leakers, and house stays comfortable. Only way you are going to use more fuel running the furnace, is if the upstairs is allowing air to leak (ie door kept open, window leaks, or left open). Allowing the heat downstairs actually helps to make the upstairs more comfortable, along with the fact that it keeps pipes from freezing. As for a cold air return, we did not install one, because the two upstairs on the floor (old house that had Octopus furnace) are enough to allow the furnace to pull return supply for the house.
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Old 12-23-2010, 11:48 AM   #5
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Heating Unfinished Basement


I'm with "beenthere" on this one, seal the leaky sill plate (great stuff expanding foam is good for that), insulate the ends of the floor joist and cut in a return, then open the supplies.

The return could be cut in the side of the return duct at the furnace and then cover with a grill that has a damper built on the back of it, return would have to be no bigger than 6" x 10".
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Old 12-23-2010, 07:29 PM   #6
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Originally Posted by gregzoll View Post
As for a cold air return, we did not install one, because the two upstairs on the floor (old house that had Octopus furnace) are enough to allow the furnace to pull return supply for the house.
Which means that the upstairs now is pulling in more fresh air from the outside to make up for the air that is being blown into the basement. Which tends to make the house drier.
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Old 12-24-2010, 01:18 PM   #7
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Which means that the upstairs now is pulling in more fresh air from the outside to make up for the air that is being blown into the basement. Which tends to make the house drier.
Have you seen my home? You are actually incorrect, because for one, the furnace is a 95% AFE, which means, any make up air for it comes from outside. The house still leaks air, because the walls are not insulated, but the drafts are caulked, and doors at the majority have been sealed to stop massive air flow.

There is enough make up air downstairs and upstairs, since for one, the company that installed the new furnace in 2005, made sure that there would be no need for cold air return downstairs, since all that we are doing, is keeping the space conditioned. Previous years, it would get down to 50 down there in the Winter, and 80 in the summer. Now since we have had Central Air installed this past Summer, the downstairs stays around 76 in the Summer, Winter it stays around 59 f, 45-52% humidity in both upstairs and basement. Temp is kept around 68 in the Winter when we are home, 62 at night, 64 when at work. Summer time, 73 during the day & at night when we are home, 76 we away for work.

There is no problem with how our unit is set up, because as stated before, the company that installed it, made sure in the calculations how much make up on the first floor, because the returns are each 2' x 3' in size, and are on the floor at opposite sides of the house (850 sqf home, built in 1937).

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Old 12-24-2010, 01:28 PM   #8
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Originally Posted by gregzoll View Post
Have you seen my home?

Yes, I looked out my window.


You are actually incorrect, because for one, the furnace is a 95% AFE, which means, any make up air for it comes from outside.

Thats combustion air that is brought in through that PVC pipe. Not the air that is blown through your house. So being a 95% makes no difference in what I'm talking about.


The house still leaks air, because the walls are not insulated, but the drafts are caulked, and doors at the majority have been sealed to stop massive air flow.

Without a return in the basement. You are putting your first floor into a negative presure because the furnace is not returning the same amount of air to the first floor as it is taking out.

There is enough make up air downstairs and upstairs, since for one, the company that installed the new furnace in 2005, made sure that there would be no need for cold air return downstairs, since all that we are doing, is keeping the space conditioned.

Keeping the space conditioned without any returns down there means your putting the basement into a positive pressure, and forcing teh air out of the basement.


Previous years, it would get down to 50 down there in the Winter, and 80 in the summer. Now since we have had Central Air installed this past Summer, the downstairs stays around 76 in the Summer, Winter it stays around 59 f, 45-52% humidity in both upstairs and basement.

There is no problem with how our unit is set up, because as stated before, the company that installed it, made sure in the calculations how much make up on the first floor, because the returns are each 2' x 3' in size, and are on the floor at opposite sides of the house (850 sqf home, built in 1937).
I'm sure the company you used knows how to defy the laws of physics.

You were told a line of BS, and you bought into it hook line and sinker.
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Old 12-24-2010, 01:33 PM   #9
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Heating Unfinished Basement


Again I think I know more about how my house is, and you can state what you want, but my house heats and cools fine, and there is no problem with make up air, or low efficiency. My Cooling bills for Electric during the Summer are around $90, Heating is around $80 for electric, $72 for Gas. So, again, tell me where the BS is? Only BS I can see, is those on here, that are "experts", that seem to think that homeowners do not know more about their own homes, than the "experts" do.
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Old 12-24-2010, 01:45 PM   #10
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Heating Unfinished Basement


Correct me if I am wrong here gregzoll, but didn't pete0403 post the original question?

He was given some good advice in my opinion, and unless you live next door to him and know exactly whats happening, why would you be so deffensive. All he has to do is read the recommendations, yours and beenthere's, try them out and see what works best for him.

My bets on beenthere's recommendations cause thats exactly the way I would do it.

Been contracting heating systems for 35 years, with all the supporting calc's, whats the worst thing that could happen, pete0403 would have to close a damper.....wooooo!
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Old 12-24-2010, 04:21 PM   #11
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Originally Posted by gregzoll View Post
Again I think I know more about how my house is, and you can state what you want, but my house heats and cools fine, and there is no problem with make up air, or low efficiency. My Cooling bills for Electric during the Summer are around $90, Heating is around $80 for electric, $72 for Gas. So, again, tell me where the BS is? Only BS I can see, is those on here, that are "experts", that seem to think that homeowners do not know more about their own homes, than the "experts" do.

And you know your heating and cooling bills wouldn't be 10 to 20% lower if you had a return in the basement how?

Its your house, its your higher then needed heating and cooling bills. As long as you are happy paying more then you need to, thats fine.
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Old 12-24-2010, 04:53 PM   #12
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Heating Unfinished Basement


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And you know your heating and cooling bills wouldn't be 10 to 20% lower if you had a return in the basement how?

Its your house, its your higher then needed heating and cooling bills. As long as you are happy paying more then you need to, thats fine.
Gee, last time I checked, Winter time heating will be higher, due to you have a Gas Furnace using a fuel to heat the space, or Electric. Has nothing to do with if there is not a return in the space. Return allows the air to circulate, so that the furnace can cool/heat efficiently. If no return, the air blower motor will overheat and go out. As for physics, air will move through a house, regardless where the air return is, since it moves through convection currents created by heated air rising, cool air falling.
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Old 12-24-2010, 06:01 PM   #13
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Gee, last time I checked, Winter time heating will be higher, due to you have a Gas Furnace using a fuel to heat the space, or Electric. Has nothing to do with if there is not a return in the space. Return allows the air to circulate, so that the furnace can cool/heat efficiently. If no return, the air blower motor will overheat and go out. As for physics, air will move through a house, regardless where the air return is, since it moves through convection currents created by heated air rising, cool air falling.
Efficiently, means it will do it better, and will cost less. The red text, is the only part that is really pertinent to what we're talking about.

The air will not circulate freely without a return. You may wander around in your bliss as much as you want.
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Old 12-24-2010, 11:07 PM   #14
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Ahh geez, I guess knowing about how a HVAC system works, but the Intertubs "expert" knows more thanz Iz doo. Guess I should go back and allow some edumacation from some odd forum to tell me something that I know. Sorry, but I know how a HVAC system works, and why there are cold air returns. Having two ducts in a unfinished basement, that is open to the main living area, is not going to cause undue harm to a HVAC system that has enough cold air return to allow for a efficient system.
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Old 12-25-2010, 05:16 AM   #15
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Ahh geez, I guess knowing about how a HVAC system works, but the Intertubs "expert" knows more thanz Iz doo. Guess I should go back and allow some edumacation from some odd forum to tell me something that I know. Sorry, but I know how a HVAC system works, and why there are cold air returns. Having two ducts in a unfinished basement, that is open to the main living area, is not going to cause undue harm to a HVAC system that has enough cold air return to allow for a efficient system.

LOL...

I was installing systems long before you heard of the intertub/internet. Got lots of OTJT, and a lot of education from the School of hard knocks.

Learned how systems actually work, causes and effect.


You keep guessing. I'll keep getting paid for what I know and do.



Have a merry Christmas.

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