# service size

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#### wire monk

##### Member
We have a house with a 200 amp service..With have 15 kw electric heat on the 2nd floor .. We want to add 15kw on the first floor. Do you think a 200 amp service is large enough?? The only other heavy load is the Electric water heater, and general lighting. Stove is gas.

#### jwjrw

##### Senior Member
I see 10kw heat on most houses here with 200a services here. But a quick load calc will tell you for sure.

#### jwjrw

##### Senior Member
30kw heat at 240 would be 156a heat load alone. So no it wouldnt work.

#### Hameedulla-Ekhlas

##### Senior Member

find out the total ampere then check the service and breaker current capacity.

#### jwjrw

##### Senior Member

find out the total ampere then check the service and breaker current capacity.
By just figuring the heat load alone you can see its too small.

#### Hameedulla-Ekhlas

##### Senior Member

find out the total ampere then check the service and breaker current capacity.

#### Volta

##### Senior Member
Probably over 200 amps. But with a full calc under 220.82 it might be closer than you think. If the "usual load is expected to be continuous" 220.82(C)(6) the heat only needs to figured at 100% for the feeder or service.

Still at 225 amps if 2000 sq ft, and that's with no appliances (disp, dw, micro, etc.). If the heat can be installed to be non-continuous then figure at 65% and it could be made to work.

#### augie47

##### Moderator
Staff member
If you go to Mike Holt's home page under technical you can find a free residential load calculator. Guessing at some parameters (sq ft, appliances,
etc) using the optional method, you could get by.
Give the calculator a try.

#### jwjrw

##### Senior Member
Probably over 200 amps. But with a full calc under 220.82 it might be closer than you think. If the "usual load is expected to be continuous" 220.82(C)(6) the heat only needs to figured at 100% for the feeder or service.

Still at 225 amps if 2000 sq ft, and that's with no appliances (disp, dw, micro, etc.). If the heat can be installed to be non-continuous then figure at 65% and it could be made to work.
So are you saying it depends on the type of hvac system installed. I think I read it has to do with when the compressor comes on?

#### Dennis Alwon

##### Moderator
Staff member
I believe many many years ago I did a 30kw (2- 15kw furnaces) on a 200 amp service. Remember that the elements are not usually 15 kw but something like 14.4kw. I think with the fan it is 15 kw.

I will never use a 200 amp for that config. again. 400 amps is the way I would handle it now. I was young and the builder was being cheap.

#### Volta

##### Senior Member
So are you saying it depends on the type of hvac system installed. I think I read it has to do with when the compressor comes on?
I don't know if a compressor is involved, could be resistance heating, probably with a blower motor, but could even be radiant I suppose (baseboards).

But even with regular calcs fixed electric space heating only needs to be 100% for feeder or service 220.51, not the 125% for continuous we think of for branch-circuits 424.3(B)>210.20(A).

Granted that 215.3 requires the OCP at 125% for continuous loads. But Art. 424 only demands that branch-circuit loads be considered continuous, not feeder loads.

May or may not be good design . . .

#### jwjrw

##### Senior Member
I read if the equipment operates such that the compressor cannot operate at the same time as the supp heat then the load can be calc at 65%

#### wire monk

##### Member
So will this work are not ?? And be safe..

#### augie47

##### Moderator
Staff member
It's borderline... until you do the actual calculations, you won't know.
There are too many variables to give a definite one way or the other.
I don't think it would ever be "unsafe" as in a hazard. If everything is wired correctly the main would simply trip were there a problem.
If it did and was continually reset then we might approach unsafe.

#### jwjrw

##### Senior Member
So will this work are not ?? And be safe..
To be sure you would have to do a load calc. Everyone seems to agree that its borderline. I would ugrade it and not take a chance you might add an electric range and or other stuff if you are going to live there for a while.

#### jwjrw

##### Senior Member
We have a house with a 200 amp service..With have 15 kw electric heat on the 2nd floor .. We want to add 15kw on the first floor. Do you think a 200 amp service is large enough?? The only other heavy load is the Electric water heater, and general lighting. Stove is gas.
Another question how big is the house? 30kw is alot of heat.

#### benaround

##### Senior Member
I'm surprized they are not going with gas heat, its much cheaper to operate and may be

less expensive to install if the service needs to be increased ? The service is close right

now, sounds like about 40 amps left for the rest of the house, EWH is 20 amps so that

leaves 20 ?? Are you willing to gamble that it will work. Well good luck with whatever way

you go !

#### jwjrw

##### Senior Member
I'm surprized they are not going with gas heat, its much cheaper to operate and may be

less expensive to install if the service needs to be increased ? The service is close right

now, sounds like about 40 amps left for the rest of the house, EWH is 20 amps so that

leaves 20 ?? Are you willing to gamble that it will work. Well good luck with whatever way

you go !
I agree but Ive heard alot of people are scared of their gas bills going crazy like last year or whenever it was. I have all elec but I saw the news and people were freaking out. Still if they did go 15k gas i bet it would be cheaper and no service upgrade. Sounds like the way to go to me.

#### suemarkp

##### Senior Member
30 KW of electric heat is over 100K BTU of heating. Do you really need this much (or do you just like to be able to heat the house quickly)? Have you made any attempt to calculate how much heat your house needs (e.g. ACCA Manual J calculation)? Unless your electric is crazy cheap, this is going to be expensive to run.

What do you have for heat now on the first floor? How many BTUs does it produce?

Finally, what type of electric heat are you installing? Baseboard? Central furnace? You have a coupe of outs depending on interpretation:

220.51 allows you to calculate less than 100% of that 15KW load if it runs on a duty cycle or intermittently. A thermostat will cause the furnace to run intermittently.
220.82(C)(4) and (5) allows electric heat to be calculated at 65% for 1 to 3 heating units or 40% if four or more. If each electric furnace is two stage, you may be able to argue that this is 4 separate units. Same with 4 or more baseboard heaters.

A heat pump throws a wrench into this, as you have to add the compressor value at 100%. Also 220.82(C)(6) could be used against you if you had a small heating system where it would be expected to run at full load most of the time.

The above rules are for new installs. 220.83(B) has the rules for upgrades, and it requires all space heating to be added at 100% and then add the other existing items as it indicates (40%).

So there are no cut and dried answers to your question without knowing more specifics or what subsection of 220.82(C) the inspector is going to let you use or are you using 22.83. I'd also be hesitant to set back your thermostats much if you're going to use the 40% or 65% sizing reductions. Kicking in a full 30 KW of heat in a marginal service could be asking for trouble.

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