BTU"s : LUSENET : Countryside : One Thread

Here's a question for the heating specalists (Hoot?). Long story short, is there a formula to figure btu's needed to heat an area? In other words, so many cubic feet per btu (or so many btu's per cubic foot). I know there are variables, such as insulation values, heat sinks, thermal masses, etc, but is there a general formula for ballpark purposes? I can give more details if needed, just wanted to keep the post short. Thanks in advance. John

-- John D in Pa (, November 17, 2000


You need to compute the buildings HEAT LOSS. Lots of variables: Insulation type, wall covering (wood, sheetrock, etc.). You need to do this for each surface, floor, roof. wall, windows and doors. Once you know the heat loss in BTU per hour, you can then size the heater. Go to the library and find a book on designing and building your own house. OR heat it with wood and when it gets cool throw on another log!

-- JLS in NW AZ (, November 17, 2000.

Hey John! The hillbilly "rule of thumb" guestimate that we use for a quick idea is kinda look the dude over. If no windows are missing, doors open etc-multiply the sq. feet by about a number 5 or 6---in this area anyhow. The less insulation, and less effecient the house is increase the multipling number. Example: A structure 32 x 48 x 8. Total square ft is--12288. Multiply by about 5 if it's fairly tight and you'll end up with 61440 btu heat loss. If the structure is not real tight multiply by about 6. If the heat loss was about 60,000 I'd put about a 85,000 furnace in. This is just an example but you can see how us'ns hillbillys'branes wurk! It might not work where you're at but imagine it would get you close enough anyhow. We never size the furnace to those exact figures but increase it some. I'd rather have one a little too big than too small. The larger one will burn more fuel while it's burnin but the burn time will be less. If the weather turns colder than normal you'll have a little extra to take care of it. The larger sizes are not that much more expensive either--depending upon the "break" in btu systems. Nuther words-a 100,000 btu furnace isn't much cheaper than say a 140,000. The break on most of'm [that I know of anyhow] is in the 150,000 btu range-- meaning a 175,000 btu would be maybe $50 higher. The other sizes are usually within $10 or so. Hey I know! If'n y'all wanna send me some cash I'll come out thar and figger that thar dude fer ya! LOL! Hope this helps--email me direct if'n ya wanna. hoot gibson--the ILLinois hillbilly. Matt. 24:44

-- hoot (, November 17, 2000.

The hillbilly brane went into overload! I wrote "square ft" and it should be "CUBIC Ft". Oh well, hit's Friday--Glory to God! Just bought tickets for a big Gospel Sing 12/2/00 at Mt. Vernon, IL High School. KIingmen and Dove Bro's. Y'all come if'n ya can! Matt. 24:44

-- hoot (, November 17, 2000.

Hi! Im Tillers husband and around these parts (Ind) Ive always used the 40 BTUs per sq ft method for houses that are anywhere near tight. If its loose at all like an old farm house, then I might go 50 per. Now that is output BTUs. Some furnaces are listed in input and some are output. Nobody's went cold yet that Ive put in a heating system for. If your ductwork is in an uninsulated place you might consider ductwrap. A larger furnace will heat quicker but then you have problems with short cycling, as well as temperature swings. In other words a waste of fuel.

-- Cindy (, November 17, 2000.

Thanks for the info, knew I could count on you guys. Here's what's up...My daughter is starting a business in an old factory/warehouse building. We have a little over 10,000 square feet of open span floor space. 12 foot high walls, 8 feet of which is glass.(on 3 walls. the 4th is solid block). No ceiling, open to the roof approximately 20+ feet up.It's the top floor in a 3 story building. The first floor is going to be a grinding shop, the second floor was removed to make headroom for the old powdered metal plant that was in there before, on first floor. Then us. We have a wooden floor and we will be gaining some heat from the grinding plant below. There is only one furnace up there now, and it's only 81,000 btu's output. We have 2 "salamanders" now, one 35K the other 115K btu's. We are located in northern Pa, so it gets a bit nippy around here. The game plan now is to see how much heat radiates up from the grinding plant below, and go from there. I'm thinking of a "false ceiling" of blue tarps at the bottom of the steel joists (?) above, effectively cutting the cubic feet in half. Then with the radiating heat from below, 81,000 btu furnace and 2 salamanders, we should get thru the first winter. If this isn't enough, I've already suggested making partition walls out of tarps, and sectioning off unused areas.Next week will be spent making "storm windows" There are 9 sections of windows, each one being 8foot by 14 foot. One whole wall (85 foot long) is done in glass block, so I'm hoping the dead air space in the block will suffice. I know it sounds like alot of work to stay warm, but the price was too good to pass up. The production floor is 120 X 85 , all clear span. This doesn't include the restrooms or our own freight elevator and loading dock. $200 a month for the first 6 months, then $400 a month for 6 months. The plant was empty for 2 years, and the company that owned it donated it to the town library, so they use it to help new businesses get started. My daughter is on a tight budget, and furnaces in the 250k btu range sell for about 1300 plus installation materials and labor, and I'm figuring we'll need 2. I can buy alot of tarps and kerosene and plastic for that. Any other ideas would be greatly appreciated. Again, thanks alot. John

-- John D in Pa. (, November 17, 2000.

John! Wow!!!!!!!!! It's beyond my old hillbilly brane to figger the heat loss. You've got some good ideas for temporary help. I might also add something else to "chew" on for a little bit. Infrared gas heaters. Radiant heat is sometimes required when it's otherwise not feasable to heat the conventional way. Other options may exist too but you don't wanna put a fortune into O.P's. property. It would be a challange, to say the least, attempting to design a workable heating system that would be affordable. If I had the time I would love to have a "look see" and try comin up with something workable--however-- I don't! Let me kinda sleep on it fer a day or two. I doubt if I can come up with anything else but who knows. Matt. 24:44

-- hoot (, November 17, 2000.

Thanks Hoot. I appreciate you "mullin" it over. And thanks for the radiant heat remark, kinda gave me an idea. The business Missy (my daughter) is starting is a parts inspection business. Around here there are alot of powdered metal plants, and they need inspection work done, to assure quality control. Most, if not all, work will be done sitting at one the tables I built for her. 4 foot by 8 foot with 3/4 inch thick tops. I'm thinking of "wrapping" a skirt around the table, and placing a small oil filled radiant heater under the table. The "skirt" will hold the heat under the table and keep your feet and legs warm. Gives me sumpthin ta think about tonite. Thanks. John

-- John D in Pa (, November 17, 2000.

Good idea about the table skirt - The Japanese do something like this around their eating table. You might want to consider using old (used) blankets for their insulating quality.

-- JLS in NW AZ (, November 18, 2000.

John! After rollin this round in my old empty haid I have a question. The folks on floor below--what kinda heat are they usin? Is it possible to cut a couple holes in the floor-install grills, and use some of their heat source to help heat your floor? Of course, I'm not talkin about stealin from'm but maybe they would consider dealin somehow for some of their heat. I doubt if much heat will migrate upstairs-at least not enuff to heat the floors to do much good. With holes cut/grills installed, one might also consider puttin in little circulating fans to help draw heat up there. A person could also build a wooden box [plywood or chipboard] with a squirrel cage blower inside and blow the heat out on the floor of your workin floor. Just an idea I had. They may not want to help out any but then again they just might. It'd probably be cheaper for you folks than to try heating it on your own. Keep'us posted. Matt. 24:44

-- hoot (, November 18, 2000.

From reading the above posts I wonder if you need all the space could you possibly screen off just a portion of the area and maybe if you do hang the tarps could you put rolled insulation on top of that also. might be worth it if you can take it if she moves. Just some thoughts. gail

-- gail missouri ozarks (, November 18, 2000.

Back when, I used to be on the maint. crew of a ski slope in NJ, and we used the infared heaters in our shop. The garage bays alone were 2 1/2 stories high, about 40 feet wide with 3 huge steel garage doors (1 bay was a "drive through"). We had 4 of those heaters hanging from the ceiling and they did a fair job of keeping it warm - but then again, after spending 3 hours sitting on the top of a lift tower anything out of the wind was warm!

-- Eric in TN (, November 21, 2000.

Well, we got some cold weather and snow. We also had our downstairs "neighbors" move in and fire up their heating system. Monday, with an outside "windchil" temp of below zero, we were able to maintain 60-65 degrees with just the one gas furness. I still plan on doing the storm windows, and possibly the false ceiling. Looks like we may be ok for now, but time will tell. Thanks for all the ideas and comments. John

-- John D in Pa (, November 22, 2000.

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