Heat loss from upstairs to cool basement

oldbrownhat

In the new house I am building, the main floor/great room/loft bedroom open area is being heated with a pellet stove & 60" ceiling fan. HW baseboards will eventually be used as backup and for downstairs heat. There is a staircase leading down to the as-yet-unheated basement workshop, which is partly insulated at present. At the moment there is no door at the bottom of the stairs as the house is not finished. As a result the temp. downstairs is about 52 deg. F.

I know that heat rises, but also that heat flows from hot to cold. Does this apply equally when the cold area is downstairs? I am thinking of my priorities here and whether I ought to get to work installing a door (or perhaps a very heavy curtain or a folding door, due to space issues at the bottom of the staircase) at the bottom before the winter progresses too far. (I'm in the Pac. NW, about 50 miles inland so winters aren't severe but we will get some snow and below-freezing spells so the pellet stove will have some work to do.)

:) Stuart.

Brad White_203

Heat rises? Since when?

Sorry to pop that bubble, but it is warm air that rises due to buoyancy. Heat itself is radiation and will go where it is not. Line of sight at first, then warm air currents will find a way up and displace air already up there, beginning the cycle... Not to dwell on the technical, just so you have it more accurately.

Now, that floor of yours. That will cool your space by conduction first and foremost. You may well have a thermocline (a boundary layer between distinctly different temperatures in a given medium, air in your case.) That may hold the colder air downward.

I would still enclose the door because the other motive force is the chimney effect. Your lower floor and upper floors, connected together, form a chimney. That will tend to draw in basement air from any opportunity it can find. The tighter the better of course.

Now, back to conduction (aka Transmittance): Your floor construction is lucky to have a total R value, uninsulated, of about 3.0 to 3.2. That will conduct 0.33 BTU's per hour per degree F. difference.

If your basement is 52 degrees, that conduction to a 70F space above will be about 6 BTU's per SF. If you have say 800 SF that is 4,800 BTU's.

All is not lost however, for this loss is also a gain to the basement. A very mild radiant ceiling in effect. Just will not be comfortable in the process, that's all.

oldbrownhat

Heat loss upstairs - downstairs

Brad,

Thanks for the clarification. I stand (er... sit) corrected. I actually meant warm air, but used the conventional terminlogy of "hot air rises.'

The basement ceiling will end up fully insulated to R-14. At the moment it is only partially insulated. The upper floor (1/2" sheathing over joists) doesn't feel all that cold but it certainly can't help. And although I hadn't originally planned to, I will likely end up insulating the basement floor - currently concrete - with 1" of rigid insulation + sheathing. I think it will be money well spent as it will reduce the load (= nat. gas consumption) required to keep the basement warm. The basement doesn't have vapour barrier in place yet but it is reasonably air tight. Once it's all sealed up there should be even less opportunity to draw cold air in from the outside.

The reason for asking this in the first place is that the pellet stove (upstairs) seems to be using rather more pellets than I had anticipated and if some of that heat is migrating to the cold basement, the stove is partly trying to heat both spaces. I'll set to work sealing off the basement.

Brad White_203

Sealing

Hope I was not giving you too hard of a time with the heat rises issue Just trying to frame the conditions.

With only half-inch sheathing, your R value is less, just under 2.0. Your heat loss per SF if 52 below and 70 above is now over 9 BTU's per SF. Same deal, just less separation I suppose!

Now, if you can, yes, insulate the basement. If you can insulate on the outside of mass (outside the concrete) that is just plain awesome. The temperature gradient will be very steady and not change much that you can tell. If your choice is to insulate the inside, well, ok, do what you can do.

oldbrownhat

Sealing etc.

No offence taken- you were quite right. It's important to get the technical jargon correct so as not to offend the Gods of Thermodynamics, not to mention make communication between mortals easier.

I can't insulate outside the foundation at this point as it's all back-filled. As this is my first house project, it is an excellent learning experience in case I ever decide to do it again (!) The next time around I would certainly put in a insulated slab and in-floor heat in the basement and probably ICF's for the foundation wall.

I will set to work finishing insulating the basement ceiling, though, and sealing off the bottom of the staircase.

Stuart