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View Full Version : OT: Figuring Required BTU's



halac
12-26-2006, 12:59 AM
Is there a simple way to calculate the required BTU's to heat one's workshop. The area I'd like to heat is 14' by 28' with 10' ceilings.

I'm thinking of using a furnace from a large motor home. They use LP for fuel and can be run on 12 VDC in case of a power outage. I seen several different models on eBay.

dicks42000
12-26-2006, 02:35 AM
Halac;
Normally when you do a heat loss calculation you consult your ASHRAE handbook, look up things like degree-days for your local area etc. and figure it out using a standard heat loss calculation method....However lots of short cuts are used/ available.
For estimating & retrofit purposes, I usually figure on a heat demand of 30 Btu/ Sq. ft. for a house of moderately loose construction with some insulation & single glazed windows in the coastal BC zone. 10-15 Btu/ Sq. ft. if the house is rennovated, current insulation, double glazed windows etc.
The R-2000 system is very stringent & requires the ASHRAE engineered heat loss calculation or other approved method, by code.
For a shop building, it would depend on how well insulated & tight the construction is & obviously where it is....Also how often will doors be opening or closing. Do you have a roll-up door ? (Notorious heat leak...)
Have you considered a radiant floor system, way more comfortable to stand on a warm floor, but expensive. Even better for an existing shop, why not go for an infra-red tube heater. They warm people & things rather than just heat the air. They can be had in Natural gas, propane or oil fired versions. More efficient to run than a unit heater in the corner....Also high intensity infra-red heaters are available for spot-heating a particular location rather than the whole space. (eg most frequently used machine, welding area....)
If you are going to have a high ceiling, a ceiling fan will be useful as it reduces "stratification" by keeping the air moving. (Hot air rises....)
Then again, I heat my 2580 Sq. Ft. sheet metal shop with a wood pellet heater & use a ceiling fan. Works OK most of the heating season. The building has 26 ft. ceilings, is block & Q deck construction with roll up doors. Works out cheaper than gas heat.
There's a few ideas, anyway....
Rick

There are a few ideas, anyhow.

ptjw7uk
12-26-2006, 06:31 AM
I think the best you can do in a workshop is heat it just enough, you would not want to do much labour intensive work if the temp is to high.
I have insulated my shop and have a low heat on at night to keep the dew point high, cover all large machines with cloth covers this is to slow the temp changes again to stop condensation. This heat will keep the shop at about 10c overnight. When I use the shop I will turn a fan heater on which will rapidly warm the air I then turn it of when it gets to 16c

Peter

Errol
12-26-2006, 04:18 PM
A furnace from a large motorhome will provide sufficient BTU if your shop is insulated. Standard Camper vans have 60,000 BTU furnaces, and our 1500 sq ft home has a 95,000 BTU unit, works well to 30 below. Air circulation will be the biggest issue, since the motorhome units are designed for ducted supply. You will need some kind of ceiling fan or???

nheng
12-26-2006, 04:21 PM
Here's a quick and dirty calculator with very basic options for insulation and construction details:

http://www.heatershop.com/btu_calculator.htm

operose
12-26-2006, 06:49 PM
here is an excel spreadsheet that has everything you need


http://eagle.bsd.st/~dertow/HeatLoadWorksheet.xls

U = u-value = reciprical(sp?) of r value
A = area
TD = change in temp