> >
>

# electric baseboard heater capacity

#1
01-16-03, 01:53 PM
coopetal
Visiting Guest
Posts: n/a
electric baseboard heater capacity

am rewiring and insulating a 20x20x8 outdoor storage area to use as an office and would appreciate insights on how to determine quantity, length and wattage of baseboard heaters. i can provide 110v or 220v. thanks.

#2
01-16-03, 04:10 PM
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 10,191
coopetal :

You will need to do a heat loss calculation for the space.
Here is a site that charges \$40.00 for a one time calculation.

http://www.heat-loss-calculations.com/

Here is one that says it's free, but I've never tried it.

If you would provide detailed construction and temperature range details, maybe someone might have a rough idea of what you need.

#3
01-16-03, 06:45 PM
coopetal
Visiting Guest
Posts: n/a
heat loss calculation is 1.2 kw

used greg's www.heatload.com calculator and arrived at 1.2 KW for my room. what's next?

#4
01-16-03, 07:17 PM
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 10,191
coopetal:

If you provide detailed construction information on your room it would give us some idea if that number is in the ballpark.
(Insulation values in the floor, ceiling and walls, window sizes and construction and temperature limits you experience. )

Once you have determined the heating requirement you would add a bit as a cushion and then divide the load between a couple of heaters to distribute the heat.

Not really sure of your climate, 1.2 kw seems kinda small .

Make sure you allow for a future a/c in the wiring plan.

#5
01-16-03, 07:18 PM
Member
Join Date: Jan 2003
Location: Plano, TX
Posts: 162
Re: heat loss calculation is 1.2 kw

Only 1,200 watts...or 3 watts per square foot?

A general rule of thumb calculation is about 10 watts per square foot, which would be 4,000 watts.

Baseboard heat usually is rated about 250 watts per linear foot. You calculation means that only 5 total feet (1,250 watts) of baseboard heat is required to heat a 20' x 20' area. Based on 10 watts per square foot (suggested above) you would require 16 total feet (4,000 watts) of baseboard heat.

You may want to check your calculation using another source.

Kooter

#6
01-17-03, 10:44 AM
Member
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,386
elec. heat

If you are after the BTUs on electric 1,000watts= 3410 btu ED

#7
01-18-03, 09:34 AM
coopetal
Visiting Guest
Posts: n/a
thank you everyone. i'll round up my 1.2 kw heatloss calculation to the 10 wats/ft sq to get 4 kw or 4 x 1000 watt heaters for the room size.

checking this, watts = volts x amps (w=va or w/a=v)

so,

4000 watts/30 amp double breaker = 133 volts so i need to use 220 v rather than 120 v

flipping this, if i plan on two 1250 watt heaters on each leg of the 30 am double breaker i get this for each leg:

2500 watts/200 volts = 12.5 amps, under the 15 amps on each side (my assumption that the amps get split between the two sides)

so i'll pull two 12/3 wires from the 30 am double breaker, one to the west side via a 220 outlet on the north wall for a future a/c unit, and one to the east side via a 220 outlet next to a door that's coming out in case it's easier to put a future a/c there. both outlets will have double 220 plugs (one for each 4 ft heating unit) and a regular 110v plug for alternative use the other 9 months of the year

that's about it, except to learn how to control electric heating from a therostat for which suggestions are welcome.

#8
01-18-03, 11:12 AM
Member
Join Date: Jan 2003
Location: Plano, TX
Posts: 162
I think you are wise to go with 4,000 watts of total heat (regardless of what various lengths you may elect to use that best fits the room's perimeter. You will find that baseboard heat is usually rated at 240 volts...(or 208 volt, which is 3-phase voltage that you do not have).

If you do elect to use four (4) 4' pieces of baseboard heat in this room each 4' piece will pull 4.17 amps (1,000 watts / 240 volts = 4.17 amps) or 16.68 amps for all four units. Therefore, since this is one large room and if it is convenient from a wiring distance standpoint I would suggest putting all four baseboard units on one circuit using 10/2 with ground romex to feed them and protected with a 25 or 30 amp 2-pole circuit breaker.

A single wall-mounted 1-pole or 2-pole line-voltage thermostat can be used to control all four pieces of baseboard heat. (You can also use baseboard mounted themostats to control the heat as well.) If you use a 1-pole thermostat one of the two hot legs is broken by the thermostat and if you use a 2-pole thermostat both hot legs is broken by the thermostat. Only one hot leg needs to be broken by the thermostat to cut off the heat entirely. Some people use 1-pole thermostats and some people use a 2-pole. It's up to you...

As far as running additional circuits for 240 volt receptacles (for your window mounted A/C units), these need to be on separate circuits and individually protected with their own 2-pole circuit breakers. Protecting each 240 volt receptacle is necessary because you may elect to use two A/C units instead of one and both at the same time...or you may have some other load being used from one receptacle while an A/C unit is being used on the other.

You mentioned that you were planning on using 12/3 with ground romex on a 30 amp circuit breaker. This is incorrect! 12 gauge wire is only good for 20 amps therefore you would want to use 10 gauge wire, which is rated at 30 amps. Also, 3-conductors with ground romex is not needed...you only need 2-conductors with ground since no neutral is required for straight 240 volts...only two hots plus the ground for safety. (A neutral wire is only needed if 120 volts is also needed, which it is not for 240 volt baseboard heat.

I hope this helps!

Kooter

#9
01-18-03, 11:12 AM
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 10,191
coopetal :

That's quite the rounding off; 1.2kw to 4kw.

Try this to polish up your ohms law calcs.
I use it all the time.

http://ourworld.compuserve.com/homepages/Bill_Bowden/ohmslaw.htm

I get just under 20 amps for 4 kw at 220 volts.

You would use a 30 amp 2 pole breaker. Run it to a two pole wall mounted thermostat rated for this load and then to your baseboards.
You can split up the baseboards to allow even heat distribution, like say 4 - 1 kw units.

Check your local code to ensure this is ok.