# Sizing Electric Baseboard Heat (Supplemental)

I have a 635 square foot finished basement insulated with closed-cell spray foam on the concrete. The climate here is zone 5A (Central NJ).

I want to add supplemental heating via electric baseboards and I'm not sure how many feet of them I need.

I read that a typical rule of thumb is to take the square feet * 10 to get the number of watts you need and then divide by 250 watts/foot to get the number of feet. (So talking 25.4 feet here).

But I believe this calculation is if you are only heating with electric baseboards. I'm looking to use these to supplement my forced air system. I have extended the forced air heating/cooling system into the basement by adding two registers and two returns, but I have only one zone for the whole house.

In the winter, when the forced air heat is running, the basement is 69/70 degrees, which is perfectly fine. When it shuts off for an hour or so, the basement drops to like 65/66. During the summer, the basement is 65/66 consistently (this is after I insulated the a/c ducts in the ceiling).

So I only really need to bump things up a few extra degrees to keep my kids from complaining.

(I would consider zoning the house into 2-3 zones. I think that would fix the basement issue in the winter. But during the summer, since I couldn't run heat and a/c at the same time, I'd be in the same position where its 3-4 degrees too cold.)

• First you need to do a heat load calculation for the size of the room, insulation rating, desired temperature inside, expected temperature outside, etc. Once you do this and arrive at a BTU loss per hour calculation you can choose how much baseboard heat you need by converting BTU's into KW's. Just know, electricity is a very expensive way to heat a building or room. Commented Sep 14, 2017 at 17:31
• I don't understand. Are you trying to use baseboard heating to compensate for temperature imbalance in your house because the forced air system isn't distributing heat evenly? I mean I'm not getting how you'd expect the baseboards to be controlled. Why doesn't the thermostat just ask for more heat from the forced-air? Gas is surely cheaper than electric, unless you have an interesting electric rate. Commented Sep 14, 2017 at 19:27
• What is the fuel for your existing forced-air system? Commented Sep 14, 2017 at 22:50
• @ThreePhaseEel Natural Gas Commented Sep 15, 2017 at 18:00
• @Harper Yes, I'm planning on using the baseboard heaters in the basement to compensate for a temperature imbalance. The basement is too cold. I could have the house zoned and this would fix the basement coldness in the winter (i.e. the heat just keeps running longer after the upstairs is warm enough). But the basement is also too cold in the summer. So zoning wouldn't help with that. Commented Sep 15, 2017 at 18:02