Heating Upstairs with FPX 44 Downstairs

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avc8130

Minister of Fire
Dec 6, 2010
1,049
God's Gift to Gassification
First let me try to explain what I am dealing with:

1 wing of my sprawling ranch house is 2x6 construction with vaulted ceilings. There are 3 bedrooms and 2 bathrooms on the "main" floor. Directly underneath is an 8' high poured foundation basement.

I am in the process of finishing the basement space. There is a Fireplace Xtrordinair 44 Elite zero clearnace cat fireplace in the basement. The walls are finished with 2x4 framing, moisture barrier and fiberglass insulation. Currently I do not have the ceiling complete, but my plan was to sheetrock with 5/8".

I would really like the heat from the basement fireplace to flow up nicely and heat the rooms upstairs.

My thought is to put some registers low in the walls of each room (probably 1 8x12 in each of the small rooms and 2 in the large master, 5 total). I would duct them right to the ceiling in the basement where there would be another register directly underneath, so 5 registers in the basement ceiling. I would then leave the door to the basement open to allow a circulation of air.

Thoughts/suggestions/concerns/experiences/cursings/ramblings?

ac
 
First, it would have been good if you had posted earlier on your plans for doing the basement walls. Assuming the 8' concrete walls are mostly buried (otherwise why concrete?), applying fiberglass insulation and vapor barrier is a no-no for that situation. Unless the foundation is in a very dry climate, like New Mexico, the concrete always will have some moisture in it. The surface of bare concrete will look dry, but that is because the moisture evaporates as fast as it diffuses through to the surface. The FG is no barrier to the moisture, so there will be moisture and possible condensation behind the vapor barrier. In summer, without A/C, if there isn't a tight air seal to keep room air from bypassing the vapor barrier and getting to the cool concrete surface, the humidity will wet the surface somewhat. The wood framing also will absorb too much moisture in that environment and over time become moldy, leading possibly to a musty smell in the basement. A better insulation method would have been to use rigid foam sheets or spray foam over the concrete. A stud wall could be built over that and infilled with FG batts, but no vapor barrier should be applied over that. It may be too late for you to change the wall insulation now, so hopefully your foundation wall is waterproofed well and has a capillary break between the footing and the wall itself. Not all basement walls finished the way you have become problematic, so I hope yours works out well.

As to movement of warm air from the lower level to the rooms upstairs, there was another thread on this subject recently, I think in the Green Room subforum. Basically, as you have worked out already, you need a circulation path for the warm air to flow upstairs and for the cooled air from up there to return to the stove. Actually, leaving the basement door wide open will do a lot of air movement by itself. The only problem I see in what you propose is the return path from closed bedrooms. Air could rise through floor registers, but the bedroom door will block the return path to the stairway door. You might have to put registers in the doors also.
 
DickRussell said:
First, it would have been good if you had posted earlier on your plans for doing the basement walls. Assuming the 8' concrete walls are mostly buried (otherwise why concrete?), applying fiberglass insulation and vapor barrier is a no-no for that situation. Unless the foundation is in a very dry climate, like New Mexico, the concrete always will have some moisture in it. The surface of bare concrete will look dry, but that is because the moisture evaporates as fast as it diffuses through to the surface. The FG is no barrier to the moisture, so there will be moisture and possible condensation behind the vapor barrier. In summer, without A/C, if there isn't a tight air seal to keep room air from bypassing the vapor barrier and getting to the cool concrete surface, the humidity will wet the surface somewhat. The wood framing also will absorb too much moisture in that environment and over time become moldy, leading possibly to a musty smell in the basement. A better insulation method would have been to use rigid foam sheets or spray foam over the concrete. A stud wall could be built over that and infilled with FG batts, but no vapor barrier should be applied over that. It may be too late for you to change the wall insulation now, so hopefully your foundation wall is waterproofed well and has a capillary break between the footing and the wall itself. Not all basement walls finished the way you have become problematic, so I hope yours works out well.

As to movement of warm air from the lower level to the rooms upstairs, there was another thread on this subject recently, I think in the Green Room subforum. Basically, as you have worked out already, you need a circulation path for the warm air to flow upstairs and for the cooled air from up there to return to the stove. Actually, leaving the basement door wide open will do a lot of air movement by itself. The only problem I see in what you propose is the return path from closed bedrooms. Air could rise through floor registers, but the bedroom door will block the return path to the stairway door. You might have to put registers in the doors also.
Click to expand...

Part 1:
I kind of stepped into this basement project 1/2-way done. The previous owners started the finishing of the space, installing the FPX 44 and setting up the walls. The electic was done and the walls complete through 1 coat of spackle. We had a water leak due to some bad caulking around a window during Hurricane Irene and this is how I found out the walls are framed with 2x4 (wood) and have fiberglass insulation with a vapor barrier. The basement is as follows: 2 walls (narrow room dimension) are completely underground with black water proofing outside. 1 wall is common to the old house basement (this is an addition). The third remaining wall is exposed with 2 windows and a sliding glass door. The concrete is painted on the side that faces the basement. I think it is some sort of water-proofing paint.

Part 2:
I had thought about the doors. My idea was to start with what I have and see how it works out with doors open as adding the vents now is easier than after the ceiling is up. If it doesn't work well with the doors open, I can abandone the idea and sheetrock/spackle the vents over. If it works well with the doors open, but not closed, I could put louvered doors on each bedroom.

ac
 
There's another current thread with a similar situation
https://www.hearth.com/econtent/index.php/forums/viewthread/91087/

Basically, what I have found is that, if you are planning on using convection (no fans), the area of the intake registers in the ceiling needs to be as large as possible and the higher the rise in the duct, the better the flow, not unlike a tall stack on a stove drawing better than a short one. My setup uses an 18 in. square register (15 in. square opening) supplying two 8 in. diameter ducts. This is 225 sq. in. of intake feeding 2 x 50 sq. in. ducts. The upstairs registers are approximately 36 in. above the floor (necessary to get sufficient continuous rise on the ducting) and there is noticeable flow out of them when the stove is hot. You can, of course, move more air with fans, but properly done they are not necessary.
 
Chances are your fan is like mine and has a tendency to move the warm air out into the room, as opposed to a wood stove that's more radiant, with more hot air on the ceiling over the stove. This could lessen the heat transfered.

(I started the other thread and am also trying to predict how/if things would work before I start cutting too many holes.)
 
I just aimed my IR thermometer at several places on the ceiling. It was 77F on the wall over the insert, and the highest was 81 in the middle of the room, while the thermostat on the wall said 75. For me, I don't think it'd look that good to have a big grill on the ceiling in the middle of the room. Just relating this to the stove fan.
 
Open a window at the far end of the house and let the FPX POS push the warm air to it. Not as far fetched as it sounds.
 
I am going to fire the FPX this weekend without the ceiling finished and see what I get. I'll try with just the door open and see how the rooms above fair.

I hadn't thought about needing the vents higher up on the walls. Using larger registers in the basement shouldn't matter as I could use the standard ones for AC and everyone would just think we actually air conditioned our basement.

ac
 
I agree with Got Wood, the posi-pressure system is supposed to move the air around in the house well if you have a window cracked, or an exhaust fan blowing.
 
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