Hi All!
My first post in this forum!
Can anyone tell me how to figure out how many feet of hydronic baseboard heater I will need to heat my attic? I will be finishing the space this summer into a family/playroom. It will be about 710 square feet. I am building four foot tall kneewalls along the length of each sloped roof, and there is a 3’x5′ double pane window in each of the two gable ends. I will be putting R19 insulation in the 2×8 rafters, and R13 in the 2×4 gables. I am keeping the space open to the peak, which will be about 13′ along the center of the house. Is this enough information?
Thanks for the help!
Norm
Replies
Do you live in the Antarctic or the Bahamas?
Oops! I guess that little bit of information I forgot is important. I live about 30 miles northwest of Boston, so it gets pretty cold here in the winter.
Im using a foot of base heater for each 25 sq ft in the rooms. Im am also hoping to renovate an attic. Did you use baffles for an air space above the insulation in the roof?
Hi Greg,
Yes, I've installed foam channels between the rafters to maintain an airspace between the insulation and the roof sheathing. Is your one foot of heater per 25 sq.ft. of room a standard? I haven't been able to find a specific number anywhere. Thanks!
Norm
This figure comes from working backwards from the energy audits I have seen for old houses here in Vermont. If you can calculate heat loss and know how many BTUH's you need, then the standard is 580 BTUH's per foot. Tis corresponds nicely with the sections in a standard radiator, too, which I have mixed in my hydronic system at home to good effect. I think there is a lot of room for experimentation, although to be energy efficient, especially if you are adding these attic heaters to an existing zone, you might want to get some engineering. I had calculations done for my home, and installed the spec-ed BB heaters, and I still feel cold in some rooms. Worst case, you try a foot per Sq. FT, and if you're cold, drain the system and add 5 or 6 feet more BB.
I don't see much hot water heat and so am a bit hazy on the details, but my understanding is that the calc depends on thetrype of baseboard unit (cast or aluminum fin) and that you need to use the same type as is already in the house.
Also, there are six inch tall and nine inch tall fin types where the larger has been set up for higher output.
There are more issues here than size of radiator if this is a hydronic system. Size of boiler and whether supply will be a new zone or a takeoff from existing come to mind. I wouldn't hesitate to have a heating engineer involved on this job.
I call my pluming/heating guy and he calls his supplier. They send their engineer out for free. There being no free lunch, his job is to sell more material but it's worth it.
That having been said, I checked from memory a few recent jobs and find that they come mighty close to one foot for every 25 sq ft of floor space.
Excellence is its own reward!
Edited 7/5/2002 8:45:20 PM ET by piffin
The attic heat will be on its own zone. We had the house with the intention of finishing the attic, so we had the boiler sized to include this space. We also had the builder run everything up to the attic we'd need (pipes, electrical wiring, phone, cable, & thermostat wire), so the construction will be straightforward.
The finished area will be 704 sq. ft., so applying the 1 ft per 25 sq ft figure gives just over 28 ft of baseboard heat. I may consult with a heating engineer as some of you've sugested, but this gives me a good idea of what to expect. I won't be doing the work myself, as I've never done any copper plumbing and don't want to start experimenting above the second floor of my house. If whoever I hire also comes comes close to this figure I'll feel more comfortable.
Thanks everyone!
Norm