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# Need help calculating heat needed.

#1
04-06-05, 03:41 PM
Member
Join Date: Sep 2004
Location: Plymouth Massachusetts
Posts: 21
Need help calculating heat needed.

Here's the scoop. The house is 4 yrs old in Plymouth Massachusetts. Full basement, not heated. Three full floors of living space plus a room over the garage (24 X 24). The third floor is not finished, yet, but I had the builder run plumbing and stub pipe for heat. I plan to add a bedroom soon. The room over the garage is my current project, it's about 90% complete. It's time to add the baseboard heat. I had the builder stub pipe (copper) for future heat in this room also. The finished space is 16' X 24' with 9 foot ceilings. One window facing north and a bank of 3 windows on the south wall. We use oil to heat hot water. I currently have 2 zones controlling heat and want to add a zone for this room and a future zone for the third floor. (the builder knew we planned to add this finished space and say's the system can handle this)
Can someone help me calculate how many feet of baseboard i'll need. I will install the baseboard and run the pipe to the boiler but plan on having a pro do the final hook up of the zone. Any help, suggestions or critique will be appreciated.

#2
04-06-05, 04:56 PM
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 14,381
Heat loss calc.

At www.slantfin.com you can get a CD with a program on it. May even be able to download the program.

#3
04-06-05, 08:24 PM
Member
Join Date: Feb 2005
Location: New England
Posts: 75
Heat Calculation

DIYJohn:

What Grady is referring to is the need to do a "heat loss calculation", which is a computer program that takes into account the many unique aspects of your building (such as how many windows, amt of insulation,etc), so that a close idea can be obtained about how many heat btu's/hour are bleeding thru the structure; the amount of baseboard installed is designed to match the heat being lost at the coldest outdoor temps & thus keep the room, or apt., warm.

The websites below offer free heat loss calculations; they may or may not be adequate for your needs; you can also Google "heat loss calculation".

I also recommend you do a "rule of thumb" calculation" to determine if your boiler has enough btu caacity to heat the added garage & attic spaces; the IBR btu rating of the boiler should be stamped on the boiler faceplate.

A "room above an unheated garage" is one of the hardest units to heat; they are notorious for having cold floors & being impossible to heat in the dead of winter; an unheated garage can drop to near 0 degrees in the winter & suck all the heat out of the floorboards in the room above; your 1st step should be to superinsulate the garage unit with R24 in the walls & R40 in the ceiling & floor; a basic rule of thumb calculation would take the square footage of the room (assuming 8' celings) & multiply by a number between 25 & 95 to get the amt of btu's/hr needed; if the garage has little insulation, above an unheated garage, you would multiply by 50 to 70; the btu baseboard output is approx 500-600 btu/hr per foot; thus 25 X25 = 625 X 60 = 37,500 btu/hr to heat the above garage room; 37,500/550 = approx. 68' of baseboard needed; this is a rough guess; you may be able to multiply by 50 if you have more insulation & thus install closer to 50' of baseboard; sometimes a diverter valve loop or prv's are used in a garage zone loop so that some baseboard can be shut off.

Even THIS may not solve a "cold floor" problem for an above-garage room; you may have to install a radiant loop in the floorboards before the room becomes comfortable.

http://www.burnham.com/heatloss1.cfm
http://www.propane.ca/resources/heatloss.asp

Last edited by Chimney Cricket; 04-06-05 at 09:06 PM.
#4
04-09-05, 09:13 AM
Member
Join Date: Sep 2004
Location: Plymouth Massachusetts
Posts: 21
heat calculation

Thanks for the reply. FYI the garage (and doors) are well insulated. The information provided was very helpful. I also remembered the builder built the exact same house less than a mile from here. That house had the third floor and bonus room finished. (I call the room over the garage a bonus room but when I sell this house it will be called a "media room". That's gotta be worth another 15 grand) I plan on asking them if I can see how the contractor finished their room and how happy they are with the heat and cooling. . (I have met them before - nice folks). No reason to re-create the wheel.

Thanks again.

#5
04-09-05, 06:41 PM
Member
Join Date: Feb 2005
Location: New England
Posts: 75
Baseboard Calculation

DIYJohn:

I incorrectly mentioned "prv" valves in my last post--it should have been "TRV" valve (Thermostatic Radiator Valve); TRV's are sometimes used to control the heat output of each baseboard unit in the room or apt.

#6
04-29-05, 08:56 AM
Pat S
Visiting Guest
Posts: n/a
Reinvent the wheel?

You shouldn't have to reinvent the wheel for this project, but this is more involved than your average DIY job! I can't overemphasize the importance of an accurate heat loss calculation to properly size your emitters. As mentioned previously, above garage spaces are notoriously difficult to keep comfortable - and comparing to similar setups should help identify their difficiencies, not substitute for specifics in your project. The Slant Fin CD is free, easy to use, and accurate if you do your homework - and will also size your emitters (BB). You can use it for the entire house and determine if your existing boiler really has the capacity for the additional loads. Good luck.