Baseboard heat calculation?

[JJWalecka]

My dilemma is such how…much baseboard heat is required in an 29 X 20 apartment. I searched the Forum and found a few intriguing statements.

Tom Baker stated
Its based on the heat loss and lowest outside air temp. in your area.
Heat loss is determined by insulation, windows and doors.

Mdshunk stated
I used to always use the "one watt per cubic foot" rule of thumb, which worked for me for over 20 years. Since learning more about HVAC, I run a quick ACCA "Manual J" calculation on the computer to get the real numbers per room.

Gndrod stated
The big question is what Climate Zone requirements exist in your area for energy heating. (in Seattle area it is 5-8 watts/sf.in lower zone 1) A 3 ft. baseboard will heat a 10 x 10 bedroom real easy. That's 750kva.

What is the Climate Zone requirements for Massachusetts near the sea board? Is there a formula that I should use? Any information regarding the amount of Baseboard heaters I would need to install would be appreciated.

Sincerely,

Justin J. Walecka

[stickboy1375]

In Connecticut, I use 10 watts per sq. ft. with 8 ft. ceilings...

[LarryFine]

A 3 ft. baseboard will heat a 10 x 10 bedroom real easy. That's 750kva.
That's quite a heater! Mayhaps you meant 750 watts? ;)

[problemsolver600]

In standard construction, Chicago area, we use 7 watts per square foot.
In sunrooms with minimal glass, 10 watts per square foot, and up from there as glass percentage increases.
Many manufacturers supplying big orange and lowe prices will have square foot figures on their product packaging.
Watch out for suppliers who sell 240V heaters but only stock one pole thermostats.
It's kind of like the "heater in a ceiling fan", where the stores advertise to install one each bedroom to save money, but don't tell you each one requires it's own circuit. Code, what code?

gary, south side of chicago

[mdshunk]

In standard construction, Chicago area, we use 7 watts per square foot.
In sunrooms with minimal glass, 10 watts per square foot, and up from there as glass percentage increases.

Which is why I don't like "per square foot" rules of thumb, because ceiling heights vary. If you consider 8 foot ceilings for both of these examples, it's still around 1 watt per cubic foot of heated space. You can't buy electric heat that close to the calculated wattage anyhow, so the difference between 7 watts per square foot and 10 watts per square foot will often yeild the same heater or heaters anyhow.

[mdshunk]

I calculate 4640 watts for that apartment if you have 8 foot ceilings. You really need to size each heater for each room, unless this is central heating. Some people will cheat the bathroom heater a size bigger (if baseboard heat) so that they can overheat the bathroom in a few minutes to make for more comfort when stepping out of the shower. For central heating, you's need one 5kw resistance heat pack.

Having said all this, the only 'real' way to calculate the amount of heat you'll need is by doing a Manual 'J' calculation.

[electricguy45]

It may not be the right way to calculate, but we've always gotten the square footage and added a zero, then round up. Here in the northeast, winters are so unpredictable, alittle over is better than under. If you figure to low, the unit(s) are going to cycle more than necessary. In that case, they might as well heat with a toaster (they're rated @ 1500W). Like I said though, we've used this calculation for 20 years and have never had a problem. True, there are alot of factors that could go into figuring this, but you should be safe using this method.

[electricguy45]

We also only put 4500W on a 240V circuit, so in larger areas, if they're open, you may need to install multiple circuits on a LV relay.

[iwire]

Watch out for suppliers who sell 240V heaters but only stock one pole thermostats.

There is no code requirement for a 2 pole thermostat with a 240 heater.

[iwire]

We also only put 4500W on a 240V circuit, so in larger areas, if they're open, you may need to install multiple circuits on a LV relay.

Wouldn't it make more sense to use a 30 amp circuit instead of adding a relay?

[George Stolz]

I use 1W per cubic foot, up to 1.75 based on conditions. I'm not sure what the climate is like on the coast of MA, so I'm not much help there.

On another note, not terribly related but relevant, I think: Keep an eye out if you ever purchase a t-stat from one of the home centers. I bought a two-pole wall stat a while back for my tack room, and the stupid thing requires AA batteries to operate, I kid you not.

If the space is seldom going to be heated (as in my case), the cold will kill the batteries before you ever get a chance to use them! I should have taken it back, but forgot. :mad:

[electricguy45]

You could absolutely use a 30A circuit, it just gets alittle tight w/ 2 sets of 10/2 in a box, though in this case, it would probably make the most sense. The relays are just another alternative, it just depends on the installation.

[stickboy1375]

We also only put 4500W on a 240V circuit, so in larger areas, if they're open, you may need to install multiple circuits on a LV relay.


I thought electric heat is to be calculated at 125%, I came up with 3840 watts max on a 20amp circuit... did I do something wrong?

[electricguy45]

4500W @ 240V comes out to 18.75 amps, 4750 is 19.79 amps, but that might be pushing it. I'm not saying that the way we calculate is rule of thumb, it's the way we do it and it has worked for us, again, every installation is different and different things have to be taken into consideration.

For example, and I 'm probably opening myself up to criticsism, but...
We recently did the fellowship hall of a church. The sq. footage of the space was 1612 sq. ft. By using our method, I added a zero and came up with 16120W required. Then the ceiling had a slope to it, with the low end being 13' and the high end being 21'. I'm not a math wiz by any means, but taking conditions and construction i.e. windows, insulation, etc. into consideration, I came up with 25,000W to heat the space. 5 5000W cabinet heaters, ea. on a 30A circuit. The units had built in relays, and they are controled by 1 LV thermostat. We also installed 5 ceiling fans to help keep the air circulating. The parishoners and church fathers are extremely happy, and so am I, we made money on the job.

[iwire]

4500W @ 240V comes out to 18.75 amps, 4750 is 19.79 amps, but that might be pushing it. I'm not saying that the way we calculate is rule of thumb, it's the way we do it and it has worked for us, again, every installation is different and different things have to be taken into consideration.

Every installation is different, one thing they all have in common is they have to follow the NEC.

It sounds like you may not have known some of the requirements.

[problemsolver600]

So I'm wrong, and a couple of inspectors too, thinking that both legs of a 240v device need to be broken by the device controller? (switch, disconnect, etc..), or am I just looking in the wrong place?


gary

[stickboy1375]

4500W @ 240V comes out to 18.75 amps, 4750 is 19.79 amps, but that might be pushing it.

I think Art. 424.3(B) disagrees with your math...

[winnie]

So I'm wrong, and a couple of inspectors too, thinking that both legs of a 240v device need to be broken by the device controller? (switch, disconnect, etc..), or am I just looking in the wrong place?

gary

If it is a double pole thermostat with an off position, then it qualifies as disconnecting means.

If it is a single pole thermostat, then it will still happily and correctly control the load, but then you need a separate disconnecting means that does disconnect both poles.

Question: can the two poles of a double pole thermostat be used to control two separate heating circuits, provided that suitable separate disconnecting means is provided?

-Jon

[big vic]

Most line voltage t-stats are rated for 22 amps

[stickboy1375]

Most line voltage t-stats are rated for 22 amps


And........? I think I missed your point?

[boboelectric]

I go 10 watts /sq ft.
Bob O.84,Pa.15330