Heating newly finished basement

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Old 05-09-09, 09:28 AM
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Heating newly finished basement

I’m finishing my basement and I’m ready to drywall but I want to address some heating concerns down there first. House specs are below:

Location – Southeastern Wisconsin (winter temps can be in the teens or lower for extended periods of time).
House – Ranch 1570 sq ft.
Furnace – Trane XR90 TUX060C936D (56000 BTU)
Finished area in basement approx. 620 sq ft open room
Basement framing 2 X 4 construction studs spaced 16” apart
R-11 Kraft Faced insulation in the walls stapled to studs.
Basement has 1 window 14” X 30”.
Hardened spray foam insulation where house sits on the foundation.
Foundation is entirely underground except top 18” or so.
Carpeting will be laid over concrete basement floor when finished.

I’m not concerned about the summer time as it stays comfortable down there during the warmer months. But the winters can get cool enough to where you would need a sweater on. This is without insulation, only block walls. It’s noticeably colder in the late fall and early spring when the ground is not frozen.
I know you’re never supposed to tap into existing HVAC runs going to registers upstairs due to stealing heat from the upstairs. I know size of furnace comes into question as well. I don’t have the money upgrade my furnace or hire someone to make all new runs to the finished basement space. My wife does not want baseboard electric heaters in either.
Would it be ok to tap into 3 or 4 of the runs going to registers up stairs and adding 6” round diffusers in the ceiling spread out with dampers so I can close them off when the basement is not being used? I would also add at least 1 return down there just off the floor to pull cold air out of the finished space and help circulate the air.
I hope I gave enough info and I appreciate any help you guys can give.
 
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Old 05-09-09, 09:47 AM
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Heating newly finished basement

If you do not add a return, the circulation will be bad.

Try what you suggested plus add a floor level return.

If it does not work, you can always shut off everything.

It does not take that much to heat a basement because the soil under the floor and the lower part of the wall will be in the upper 50's and you do not have any air infiltration.

There is not a computer program around that will accurately give you the heat loss for a basement since they are really not that sophisticated. - Just a "turn the crank" calculation based on R -values of lightweight building materials and influenced by the pink panther.

If you have a variable speed fan on your furnace your basement can be a real asset thermally. I have a split entry with a sliding door on the lower level, and I can maintain a 1.5 degree difference for up to down even with a open stairway. - 80% efficient with a variable speed and I have never been over $110/mo (heat plus hot water) - only 1 or 2 months in the winter and my water heating and service charge is $20/mo.for gas in Minneapolis/St. Paul.

Dick
 
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Old 05-09-09, 10:43 AM
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Thanks for the reply Concretemasonry. My furnace is not a variable speed. I almost think after looking online that the furnace is almost undersized for the upstairs alone which surprises me.

I have a wall built just below an area where that silver thermal cardboard is fastened to the joists above to tunnel return air from upstairs to the furnace. Can I box off that portion of the wall to make a tunnel under that area, cut a hole in the cardboard within that boxed wall so it tunnels through the wall and add a cold air return just off the floor? Or would I need to make a whole new run from the furnace?
If I add three or four 6" round diffusers in the ceiling how big of a return register do you think I would need?

I'm not looking for it to be perfect down in the basement, just comfortable enough to hang out down there in the winter. I don't expect it to be as manageable as the above ground level, I just don’t want it to be too cold that we never want to go down there. There will be a home theater down there and we watch more movies in the winter. Plus I’ll be watching football games as well which is in the colder months.
Every wall touching an unfinished portion of the basement will also be insulated with R-11, plus I’m considering putting in insulated doors in those areas as well.
Not sure if it matters or not but the ceiling will have non-faced R-11 insulation between the joists only to act as a sound barrier and then covered with 5/8” drywall.
 
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Old 05-10-09, 07:28 AM
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Basement

Instead of tapping into the duct runs for upstairs, I'd suggest coming directly off the main trunk with new branches for the basement room. A return or two is a must. How big is the newly finished room?
 
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Old 05-10-09, 07:39 PM
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The finished space is about 620 sq ft. This is the family room. There is actually more. My daughter’s bedroom is down there already and there will be a bathroom and another small storage room for the kid’s toys and stuff.

My daughter’s room which was built last year around September has a heat duct coming right off the plenum but has no cold air return in it. I'm planning on putting a pass through in the wall once the basement is finished so air can circulate from her room to the finished basement area once everything is done. The bathroom I plan on putting in a heater fan so I'm not concerned about adding it to the existing HVAC system. Besides, the door will be open almost all the time.

I thought about running new runs from the Plenum but I'm limited on cash right now and would like to get it done as soon as possible.
The upstairs has 6 registers between the kitchen, dining room and living room. The runs I would be tapping into run each to one of those so there would still be one in each room that would be by itself without being tapped into. That's why I didn't think it would be that much of an issue if I tapped into them. Maybe I'm wrong though. Plus if it doesn't work out I can always close them off with the dampers so I figured I had nothing to lose.
Maybe I'm wrong though?
 
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Old 05-10-09, 08:07 PM
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Branches

I think you will be shooting yourself in the foot if you try to tap into the existing runs.
 
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Old 05-11-09, 07:14 AM
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Ummmm. Interesting design method --- building the space first and then figuring out how to heat it!


You conclude that the current furnace is just big enough to heat the existing space. That suggests it was properly sized for heating that space. Properly designed heating systems are designed to heat the space properly on a "design day" the coldest day you will typically get during the winter.

That means it might be somewhat undersized when heating the house on an unusually cold day.


On the bright side, most days are going to be warmer than the design day, which may allow you to heat your basement adequately during much of the winter.

But on cold days, you may want a way to shut off the heat to the basement so the main part of the house is adequately heated. That suggests that you may want to install dampers so that heat to the basement can be shut off when it's needed elsewhere.

This isn't a bad arrangement, it's just something of a compromise.
 
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Old 05-11-09, 09:09 PM
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I will admit the thought of heating the space never occured to me when I started the project. It was late summer when I started and comfortable down there. I wish I would have now.
If there are dampers in the registers I install so I can close them all off, wouldn't it eliminate the "stealing heat" from the upstairs if they're closed? If I find out this doesn't work I could always close everything back up and look into other alternitive ways of heating later on right?

I appreciate all of your advice so far. I am a little worried about tapping into the existing runs after all of your comments and everything I've read on it.

If I did decide to make a new run from the plenium would I be able to make one main run with a larger round duct then split that off to three or four smaller runs to each register?
I would then put a main damper in right off of the plenium to cut off air flow to the basement entirely.
 
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Old 05-12-09, 06:29 PM
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Main Duct

The running of an new main with branches is the way to go. Install a damper in the main as soon as it comes off the plenum & dampers for each branch.
Now the question is: How much heat do you need for the newly finished basement room? Without that information, you, me, or anyone else is guessing on the amount of ductwork you need.
Here is a link to a program which will answer that question. It could very well be the best $50 you spend on the whole project. HVAC Software, HVAC-Calc for Heat Loss, Heat Load Calculations
While you are doing the new room, you can & should do the whole house. At least then you will know how much, if any, heat you can take from the main house to heat your new room.
 
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