Thread: Determine electic furnace capacity

I must admit i really don't know how to read an electric furnace tag to determine capactiy any advice?

Originally Posted by cory nystul

I must admit i really don't know how to read an electric furnace tag to determine capactiy any advice?

If the installer was kind enough to mark the label, it will be in KW. If not you would have to remove the cover to count the number of strips (that is beyond a normal HI). Conversion to BTU is approx 17000 BTU per 5KW strip.

Most of the time you can not tell by the tag. Some older units have the kw rating on them, others may have a clue in the model number, but many units do not come from the factory with heat strips installed, they are added after the fact.
On a recent inspection I found a Rheem heat pump. The m/n was RBHA21 J15SFAAI and it had 14.4 kw heat strips. You might conclude that the 15 was the heat strip rating.
I always open the front to get a look at the heat strips. Not only can you tell what size the unit is, but you also might find melted wires, etc. Once in a while, I find a heat pump without any heat strips installed.

10 gauge AWG - 30 amp = 5 KW furnace
6 gauge AWG - 70 amp = 10 KW furnace
4 gauge AWG - 100 amp = 15 KW furnace

1 KW = 3,412 BTU per hour for heating

Originally Posted by Raymond Wand

30 amp = 5 KW
.
.
70 amp = 10 KW
.
.
100 amp = 15 KW

???

You are calculating based on 240 volts or ???

Originally Posted by Jack Feldmann

Most of the time you can not tell by the tag. Some older units have the kw rating on them, others may have a clue in the model number, but many units do not come from the factory with heat strips installed, they are added after the fact.
On a recent inspection I found a Rheem heat pump. The m/n was RBHA21 J15SFAAI and it had 14.4 kw heat strips. You might conclude that the 15 was the heat strip rating.
I always open the front to get a look at the heat strips. Not only can you tell what size the unit is, but you also might find melted wires, etc. Once in a while, I find a heat pump without any heat strips installed.

Hi jack, not familiar with heat strips. Do you have a picture you can share.? In my area I don't see many electric furnace in area.
Thanks

Interesting. I see an electric forced air furnace maybe once every other year and a heat pump maybe once a year.

So, I would "assume" that a 15w unit would be for a relatively small home, 1100-1400 sq ft. in a cold climate.

Hey Lonny, it's KiloWatts, not Watts.

We expect to see a 70 to 100 amp unit for an average smallish 3 bedroom house, and they go up to 125 amp. I don't recall seeing one bigger than 125 amp here but we have mild winters so the heat pump does the bulk of the heating.

50 amp is about the right size for a manufactured home.

Please remember to turn off the breaker before removing the cover. This is lethal voltages and the ends of the elements are exposed when you pull the cover, a big piece of metal.

Originally Posted by John Kogel

Hey Lonny, it's KiloWatts, not Watts.

OOPS, typo.....LOL 15w is a space heater.

Originally Posted by Lon Henderson

OOPS, typo.....LOL 15w is a space heater.

No, 15 w is a night light

Fidel, just for you, two pics of an electric furnace. They are boring to see.
This one was interesting because the builder never got around to installing any ducts in the crawlspace. So I got a shot up into the furnace from below. It was toasty warm down there too.

Originally Posted by John Kogel

Fidel, just for you, two pics of an electric furnace. They are boring to see.
This one was interesting because the builder never got around to installing any ducts in the crawlspace. So I got a shot up into the furnace from below. It was toasty warm down there too.

John, thanks so much for the pics and your time. Very helpfull