Anybody have a set rule for how to figure out what wattage heater to use in room additions, or anywhere else where new space heaters have to be installed -- other than some complicated heat loss calculation?

The ony way to get a real answer is "some complicated heat loss calculation" Lattitude, number of windows, insulation value, which way is south, if adjacent areas are heated, and lots of other things mean the same size room can have heating requirements that commonly vary by as much as 400%.

A basic rule of thumb, which I have used successfully:

Well insulated room-- 8-10 watts/sq. ft.
Moderate insulation-- 10-12 "
Little or no insulation-- 12-15 "

Place electric baseboard heaters under the windows for better performance. In large rooms, install multiple smaller units (on exterior walls) for better heat distribution.




[This message has been edited by Redsy (edited 02-06-2003).]

I agree with Redsy I generally figure 10 watts per square foot unless I know that there is an unusual amount of heat loss.

Well it looks like my usual 10Watts/sq ft method (for baseboard heat) is in the 'rule of thumb' ballpark. Thanks Maintenanceguy for the 400% figure. I never tried to see just what the variation might calculate out to be.

My house has just electric baseboard heat with individual thermastats in each room.

We can keep the house or any room at 70 degrees with the outside temp at zero using the 3.5 watts/sqft we have installed.

I remember it being minus 15 a couple time long ago. I remember being cold in the house.

My low of 3.5 watts and Redsy's high of 15 watts are 400% different. I suspect you can find larger differences.

I would use the same watts/sqft as the rest of the house uses for its furnace. (You need to change BTUs to watts.)