sizing a stove: square feet vs cubic feet?

[markleyh]

I've been thinking again, always a dangerous avocation. Our Fireview works pretty well to heat our 1900 square foot two-story contemporary, but it doesn't really make it HOT the way I expected it would. Saying we have 1900 square feet isn't the whole story, though. The house is a Lindal Cedar passive solar design with a massive southside greatroom/dining room rising up to a gambrel ceiling 25 feet above the floor. Two second-floor bedrooms open onto a loft balcony overlooking that space, which also contains a 12' X 2' X 25' bluestone 4-flue chimney chase (solar mass, dontcha know). Theoretically, if we wanted to open a hostel, we could put two more floor levels over the Greatroom, with 8' ceilings for each one. That would add up to probably 2800 square feet of living area but I am too lazy to calculate all the cubic feet in the house, what with triangular prism shapes and trapezoids, and high sloping ceilings upstairs, etc. It seems much bigger than the supposed 1900 square feet, anyway. I am thinking that this is why the Fireview doesn't heat to the max.

Anyway, I was wondering why we calculate square footage of floor space for heating needs, rather than looking at heated volume of air to be heated. I guess there is an implicit assumption that the ceiling heights are 8 feet for the standard square footage. But I'd like to hear people's thoughts about sizing stoves by volume of heated area rather than what I am thinking now is inaccurate room area.

Especially interested in thoughts from Woodstock along these lines, as I know they are active in this forum.

Thanks for reading!


herb

 

[madison]

As you and I and everyone else has realized, sq ft references for stove sizing are pretty much worthless. Location of house, ceiling height, windows, insulation, current furnace btu rating and how much it is working etc. give you more of a clue than the sq ft of a home.

 

[begreen]

You are very correct. Stove sizing can be hard due to the variance in houses. Fortunately most people have averaged ceiling heights somewhere between 8-10 ft. which makes for a somewhat consistent target. It's often hard enough to get the sq footage heated from a poster here and a decent description of the house, never mind cubic footage to be heated.

But it is important and you are discovering what was found back in the early ages. Heating a cathedral is hard. Are you assisting the stove with ceiling fans? Are there insulated shades covering the large glass areas at night?

 

[markleyh]

Thanks. Yes to the ceiling fan, which is indispensable, plus a stovetop ecofan and a doorway muffin fan aimed toward the first floor North bedroom. Heat loss is much less with new windows last year, equivalent of triple glazing. We took out the window covers after they wore out and didn't notice a difference unless it got to -20 degrees, only twice a winter.

A bigger problem is the 2X4 construction of the home, but can't fix that without a rebuild. It's tight, anyway.

 

[joefrompa]

I'll add that, IMHO, the matter of home heating should be viewed similarly to maximizing refrigerator efficiency: the more conditioned air space, the easier the temp will fluctuate. The more conditioned mass, the more stable the temp.

Like you described, Cubic feet is a much better assessment of the interior volume needing to be heated. If you kept going though, should you try to assess the amount of temperature stabilizing mass as well?

For example: A stonecountertop is a huge heat-stabilizing element - it absorbs a lot of heat, sure, but it will also help your home stay far warmer when you open and close an outside door a few times. A very full house with iron/wood furniture and decorations will have a much easier time staying heated than a spartan home...

Just something to add to the mix

 

[mtcates]

I'm with you on the cathedral ceiling hard to heat. I've got 1620 square feet but the volume of a normal 2200 square feet house. The entire front wall of this room in the picture is glass and there are no window treatments to help hold the heat in at night. I figured the mass of my interior chimney is about 20 thousand pounds of masonry. It really helps heat the house if I get behind on the stove but If I get behind too far and it gets cold, boy is it hard to heat the 20 thousand pounds back up.

 

[begreen]

Seems like a well made masonry stove would be ideal for this type of installation.