How big of a stove do I need?

[frazwood]

Does anyone know how to compute the amount of heat (BTUs/hr) that I would need for supplemental heating for my walk-out basement?

I've found some websites, but the techniques all seem very crude (for example, take the volume of the room and multiply by 3 to get BTUs/hr!).

I have a 600 sq ft room (~20ft x 30ft, two of which are exterior walls) that is cold in the winter (high 50s/low 60s). I'd like to supplement the heat with a gas stove into the low 70s, on occasion, for things like watching TV.

I went to a fireplace shop today and the salesman basically said "you need this one" and refused to even discuss calculating the heating requirements. He kept saying things like "you want to make sure that you have heat in case your furnace goes out" which is precisely what I do NOT want.

p.s. I'm a civil engineer, so I have some grasp of thermodynamics, but I've never actually done calculations like this before

p.p.s. Yes, I could go to a different shop, but I've heard good things about this place as far as their installation and service after the purchase

[delcecchi]

There are a bunch of sites with calculators for doing this or you can do it yourself. I searched "calculate heat requirement"

You might find http://www.dimplex.co.uk/products/domestic_heating/portable_heating/how_much_heat_do_i_need.htm

of interest.

R value is 1/((btu/hour)/ft**2*degreesF) as a reference.

Use the R values for insulation for external walls, derated for studs. Look up any windows and doors.

dimplex calculator says you need 31k btu at -30C assuming that is the only heat source in the room. I don't know how much heat you would get from the furnace with the heater running. All depends on how the zones are set up.

Anecdotally, I have about a 30k btu fireplace and it will roast us out of the living room even if it is really cold out, and my house has 1959 grade insulation in it (and is open to dining room and kitchen so outside walls on 3 sides and about 600 square feet.)

I bet a electric space heater or two would do the job, actually. In fact that would be a good experiment. Get a 1500 watt space heater (5000 btu/hr) and see how much it raises the temp of the room. I heat our 600 sq foot uninsulated cabin with a 2000 watt baseboard and if real cold, a 1500? watt tower style space heater and get at least 40 degrees of delta T

[MNice]

Don't over think it.. your basement is heated already, so the temp rise needed would only be about 10-15 degrees. Buy one that you want, even the smallest gas stove will do what you need.

[SkunkedAgain]

I finished my basement three years ago, which is about 15 x 30 with three of the walls exterior cement blocks. I insulated with rigid foam and then sheet rocked the walls. On the long wall with two exterior windows I used electric baseboard heaters. I thought about a stove but didn't want to deal with something taking up valuable space. I only turn on the heaters when we plan to be down there and they do a perfect job. It's another option for you

[aanderud]

If you're just heating the basement and need to go from 50 to 70, I think ANY fireplace ought to work.

My 4 season porch is 300 square feet and has just a baseboard heater on it. There are 4 walls and air underneath it, as it is elevated. It has a door on the corner and otherwise has 4 walls AND a floor exposed to elements, and I'm heating it from 0 degrees or colder to TV watching temps with just a baseboard heater on one wall.

[fishfinder72]

If you are looking for a fireplace to supplement heat for when you use your basement check out Kozy Heat fireplaces made in southwest MN. I have one that is approximately 28,000btu in my basement and does a great job. I do not even run a blower in mine. Not only is it nice for the supplement heat but I enjoy a nice looking fireplace much more than a baseboard heater.

[LightningBG]

If you're going to do a fireplace, I'd make sure to get a blower. We have one without a blower and it's nearly useless for heating.

As for BTU, I'd get a little 1500 watt space heater and test it out. Pick a nice cold sunday. Turn it on at 9am, go down and check it every hour or whatever and see how fast it's bringing it up.

Can get one of these guys at the M store for under 100 bucks.

[frazwood]

Thanks for the comments everyone.

We could have gone with an electric space heater, but we wanted a fireplace/stove for appearance reasons.

Being an engineer, I have an intuition to do calculations to determine the correct size for something like this, rather than simply trusting a salesperson who knows virtually nothing about my house, math, or thermodynamics.

When I revisited the same store and talked to a different salesperson, he also pushed me towards a stove that was bigger than I wanted. When I challenged him on the math/heat calculations, he changed his story into a different reason why I wanted a bigger stove. For whatever reason this store was really pushing bigger stoves (my guess is that they have a bigger profit margin or something).

I also "learned" all about how "cheap" these stoves are to operate (less expensive than my 95+ efficiency furnace? I don't think so...), etc, etc, etc.

Anyway, this all turned out to be a moot discussion. Whereas I like the smaller stove (for appearance and for being the correct size), my wife liked the bigger stove for appearance, so you can guess which one we are getting.