Wood Stove/Insert Specs

Everywhere I look at wood stove and insert specs, I find they say they will heat X many square feet. That would mean everything is on a linear plane and really doesn't tell the whole story.

For instance, the inside of your home is roughly 1500 square feet. But how high are the ceilings? If your heating a 1500 square foot area, aren't you trying to heat the entire space? So if you have 20 foot ceilings with loft style bedrooms aren't you actually trying to heat 30,000 cubic feet? But if your on a single level 1500 square foot home with 8 foot ceilings, aren't you heating 12,000 cubic feet? So why don't the manufacturers state in cubic feet rather than square feet?

I know I heat cubic feet, using cubic feet of firewood.

Even then those are just generic numbers not taking into consideration how much insulation is installed, how many windows there are. Are they double or triple insulated? Are they wood, aluminum, or vinyl?

A little US Stove 1100 can heat a 20,000 cubic foot home that is heavily insulated, where a stove designated to be able to heat 3000 square feet might not be able to keep up with a poorly insulated 12,000 cubic foot home. That's assuming under each circumstance that they are burning well seasoned (3 year or longer) firewood.

So, do y'all heat cubic feet? Or square feet?

 

Neither, heres a little fact. The manufactuterus determine the square foot rating of the stove. It's really an arbitrary number based on the btu's the stove can put out... it's handy for comparing stoves of the same brand but not for one brand to the next.

The buying decision should be based on BTU'S produced from an EPA tested stove. Compare that with the amount of energy you use in oil or electric and then round up to the next size bigger. You'll find that fire box size has everything to do with how well a stove can heat, and how long it can heat for. My 2.85 cubic foot blaze king does a fine job of heating my 950 square foot basement, my 1100 square foot 1st floor, and when its not too cold i leave the door to the basement level gararge open and it helps out there too....

All stoves are different, if in doubt BUY BIG!!!!

 

One might presume that manufacturers are using sq ft in their calcs, yet in the real world, some homes have vaulted ceilings. Lots of rooms with small openings, tri-levels, etc., don't help either.
I've often wondered how well the 30 would do in such a home, as opposed to my humble little abode with a pretty much open floor plan and just a hair under 8' ceilings.
As you noted too, insulation plays a huge part. Even the 30 struggles to keep this place at the temp we like when it's below zero, since the insulation isn't where it should be.

Gooder question.
Like bobdog said, I did a calc based on nat. gas use, and extrapolated to get an approximate btu amount, then compared that to btus in a cord of Oak. Surprisingly, the numbers (which I don't remember exactly) matched very closely with our firewood use (at the time, it was all Oak).
I hesitate to give my thoughts on marketing tactics.

 

I edited the last line of my post to read square feet instead of linear feet.

But the question remains, do you heat cubic feet or square feet with your 2.85 cubic foot firebox stove? Or do you heat with square feet of wood? So how many square feet of firewood do you go through a season? I go through 192 to 256 cubic feet worth of firewood with my 1.8 cubic foot firebox inside my wood burning stove which has the capacity to emit 60,000 BTU's if I am burning good seasoned firewood. A wood burning stove on it's own produces zero BTU's. (it needs firewood to burn and fire to ignite it)

Yes, I'm pulling your chain!

 

I'm sure everyone's usage varies and for my situation, I could have easily used two 30NC's with the amount of fuel I went through my first year here. By the second year I had added the wood stove (US Stove APS1100B) and eliminated the propane leaving the oil stove. After many modifications to my home, and I'm not done yet, I eliminated the oil burner leaving just the wood stove. It was large enough to heat my home, but aesthetically, it was just plain too small. So I sought out one with a larger capacity and larger viewing window. BTU wise, it's smaller. the US Stove has the potential to emit 67,000 BTU's with a 1.2 cubic foot firebox while the 13NC has the potential to emit 60,000 BTU's with it's 1.8 cubic foot firebox. (It heats well and really is more efficient overall)

At this point, I could probably get away with a wood burning stove half the size of the US Stove. That's with my home not having an open floor plan, though I will be changing that. I have yet to use the fans on either stove. The US Stove now resides in my garage for heat in there. It struggles because there is no insulation to help keep any heat in. But when I build a new garage, it will have plenty of insulation.

Where I live though winters aren't nearly as harsh as those experienced by those much further north, but it does get cold here and with the altitude I live at the winds also play a big factor. During the winter months it seems as though I'm living right in the jet stream.

So how can a 13NC heat better than the US Stove with a lower potential BTU output? And where do those BTU numbers come from anyway? Did US Stove used coal when determining the potential output of the stove while the Englander used seasoned oak? I suspect the US Stove to have the actual potential of 40,000 BTU's instead of the 67k. I'm inclined to believe it is more marketing than anything.

Still, I heat cubic feet with cubic feet of firewood producing whatever BTU's. How does one measure a cord of firewood (128 cubic feet) using square feet?

 

^^^^

Right there with ya'......
This should open up the usual can of worms, but it's the reason there's no "official" face cord other than the sq. ft. measurement of 4x8'. That measurement is only the face, or facade. Doesn't mean much w/o the 3rd dimension.

 

There ya go! the 4x8 measurement is fine for determining area. The third dimension is needed to calculate how many cubic feet there are. I could just see selling a face cord on eBay for $65 which includes shipping (cash only) stating the measurements are 4x8 and have a picture posted of the said face cord on a black or dark brown background. The pieces of wood are 1/16th of an inch thick which is the reason for the dark background. The deal is made and all of the pieces are carefully packed in a 2 cubic foot box and send UPS. The person receives the package and soils themselves when they find out this is the "Well seasoned face cord" they paid for. That third dimension is really important!

Okay, back to the other situation. If I'm looking to put in a new floor, the length and width measurements are important to calculate the amount of materials to be used (add 5% as a margin for error) for a given area. My floor measures 960 square feet. My roof on the other hand measures 1554 square feet. (one foot overhangs on 3 sides, and the 4th having a 2 foot overhang over the front of the porch) But I'm not heating the area, be it the floor or the roof. I want to heat the space between including the floors, walls and ceiling. That means I need a cubic foot measurement. Mine would be 7680 cubic feet.

In order to heat one cubic foot one degree, you need 0.24 BTU's. Without going into fresh are intake which is necessary for any heating appliance we need to calculate the cubic feet for inside the home. (calculate the outside measurements for floor space because after all, you are also heating the floor, walls and ceiling. If you need to raise the air temperature 30 degrees, the difference between the outside air and inside your calculations would look something like this (using my measurements) 960 x 8 x .24 x 30 = 55,296 so my needs would be 55,296 BTU's per day. This is assuming an average amount of insulation with average air leaking around doors, windows, pipes, and outlets.

Those calculations will only work on this planet, not the moon or Mars since air density is much different. Air on this planet weighs about .075# per cubic foot in normal atmosphere.

So there y'all have it. It's the length, width, and wall height to give you your cubic foot measurement. Then multiply by .24 for the BTU's necessary to raise the temperature by one degree. Then multiply the difference between the outside air and inside to determine your BTU needs.

 

Now my head hurts.

 

Just think, it could be worse, I could have included a Psychrometric Chart and given calculations based on that, but I decided to go easy!

 

I like learning new stuff.
Nice chart.

 

Probably because most homes are listed in the square footage of the homes and they just use that as a rough guide. You are correct though that you are heating the cubic feet of air space plus all the square footage of surface area in the walls and ceiling. Then you have to deal with the temperature gradient from the floor to the ceiling; if there are tall ceilings with no means to move the air, then you have to create more heat to be comfortable at the standing height because of the heat rising to the ceiling.

 

Or we could look at the 3D graphs of pressure, volume, and temperature.

 

I firmly believe the calculations of most manufacturers are SOO optimistic it's almost .. yes Star Gazer , I heat cubic feet because the 1800 square feet of my house above the woodstove, 1400 feet of that has vaulted ceilings where 1 side is 17 feet high anyway. but are we forgetting it's as much about where you heat as what! meaning the 45th parallel is generally colder than the 40th...

 

I think most of us go by firebox size and efficiency numbers. After all, a stove is considered a space heater right? They are giving you an idea of the capability of heat load a stove can supplement with.

 

I recently built a house with cathedral ceilings open to a loft and upstairs bedrooms. The room with cathedral ceiling has 123 square feet of glass/windows. Total first and second floor footage is 2400SF. The Osburn 2400 insert, which is a 3.2 cubic foot box, has no problem heating this area. We run ceiling fans and the upstairs gets toasty. Only issue is the master bedroom and bathroom is on the first floor but off to the side and its hard to move the heat to that area which the boss reminds me of quite often. The Osburn is rated for 2700 SF of heating and it heats this area no problem. If you had a 4000 SF space insulated with no windows and completely open floor plan I am sure you could heat it with the Osburn. As stated above, I think the manufacturers back into the square footage number using the max btus from the fireplace and a standard for btu to square footage ratio.