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Old 06-22-2011, 03:11 AM   #1
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Electric HVAC on 100 amp service?


Hey guys, need some more opinions! I know the usual answer to someone asking about putting full electric HVAC on a 100A service is NO! But my house has two separate 100A services, and virtually nothing except the computer I'm typing this on is running off the second floor's service so I thought it might be prime to be used for our main HVAC?? Crazy??

Now that I think about it, the water heater is on the second floor's juice, but if need be I can move that over to the first floor as well. House used to have two water heaters as well, but we ditched the first floor's when we converted to single-family, but the breaker and wiring is all still there.

Any reason I can't do this? I'm thinking about a High-Velocity system as it's an older house and there's no room for ductwork to second floor.

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Last edited by DoctorWho; 06-22-2011 at 03:18 AM.
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Old 06-22-2011, 07:39 AM   #2
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Electric HVAC on 100 amp service?


Why do you have 2 100 panels??? Not important. Yes you can probably install A/C. Follow the manufacturers instructions for breaker/supply requirements. How the unit delivers the air has nothing to do with how much power it uses. Most A/C units require 30-50A at 240V.

Judging from your question, I hope you are not planning a DIY installation. Please get a pro.

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Old 06-22-2011, 05:07 PM   #3
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Electric HVAC on 100 amp service?


lol, no, I don't plan on a DIY hvac install!! Just wanted to know if it was a reasonable thing to do so when I have a guy come out for an estimate he doesn't try to BS me that I HAVE to upgrade my power as well. House has 2 100A panels since it used to be a multi-family, has 2 meters too. Thing is I'm not just talking A/C but I want electric heat too, still enough juice for that? House has an oil hot water boiler for second floor and oil forced air furnace for first floor, both of which are decrepid, already dismantled the boiler, and want to replace the forced air unit with a whole-house all-electric one.
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Old 06-22-2011, 05:24 PM   #4
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Electric HVAC on 100 amp service?


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Originally Posted by DoctorWho View Post
lol, no, I don't plan on a DIY hvac install!! Just wanted to know if it was a reasonable thing to do so when I have a guy come out for an estimate he doesn't try to BS me that I HAVE to upgrade my power as well. House has 2 100A panels since it used to be a multi-family, has 2 meters too. Thing is I'm not just talking A/C but I want electric heat too, still enough juice for that? House has an oil hot water boiler for second floor and oil forced air furnace for first floor, both of which are decrepid, already dismantled the boiler, and want to replace the forced air unit with a whole-house all-electric one.


Now that is a horse of another color.

An electric furnace could well be up to 100 amps alone.
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Old 06-22-2011, 06:57 PM   #5
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Electric HVAC on 100 amp service?


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[/b]

Now that is a horse of another color.

An electric furnace could well be up to 100 amps alone.
Crap, that's what I was afraid of jb, thanks though. Is it possible to combine the two 100A services into a single 200A or would it be better (cheaper) to just upgrade one or both to 200A individually?

Don't know that any of this will happen, just wondering what kind of options I might have. Money is always the issue unfortunately! Probably gonna have someone out in September to take a look.
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Old 06-22-2011, 07:07 PM   #6
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Electric HVAC on 100 amp service?


Are you sure those two panels don't go to an existing 200 amp panel somewhere?
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Old 06-22-2011, 11:27 PM   #7
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Electric HVAC on 100 amp service?


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Are you sure those two panels don't go to an existing 200 amp panel somewhere?

Quite sure, have 2 meters outside, get 2 bills!

One meter drops into a 100A breaker panel, the other drops into a beefy fuse box with two 100A fuses, one for each leg I guess.

Any ideas why the guy that did all of this would put a fuse box in for one floor? It's not really old or anything, all of it was done in the mid-1980's! Thankfully he removed all the old knob & tube!
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Old 06-22-2011, 11:40 PM   #8
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Electric HVAC on 100 amp service?


Don't know about Boston, but in Toronto (similar climate!) you'd need a permit for what you want to do and if you want to change from gas/oil to electric heat, you also have to upgrade your insulation. For example, with new build, wall insulation requirements are R20 with gas and R28 with electric, if you want to switch an existing house, you need to have an assessment done of your current R value and upgrade to retrofit minimum requirements. Never gone from gas to electric, so I don't know the values off the top of my head. Also, FWIW, electric is significantly more expensive to operate!
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Old 06-23-2011, 01:02 AM   #9
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Electric HVAC on 100 amp service?


Have to disagree with you on the cost, I've had gas/propane/electric and now oil systems and in my experience gas is the most expensive (had monthly bills north of $500!) electric is usually around $200-300 a month, compared to oil/propane where I have to fill a tank twice or more per winter at $1000+ a fill.

Don't think I have to have any insulation at all around here. House is 111 years old.

I am considering the fact that I may have to just upgrade to a better oil system but I really don't want to. It would mean I'd have to replace the fuel tank and replace a 40ft chimney sooner rather than later if I keep an oil system.

Anyone have any opinions on my current furnace? It's an Armstrong Air Ultra 80, energy guide label puts it at the very lowest possible rating as far as efficiency and that's when it was new, I've found old paperwork in the basement that showed it was failing efficiency tests back in the 1990's. I don't even know if it works at all really, worked during inspection but haven't used it since then 2+ yrs ago.

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Old 06-23-2011, 08:58 AM   #10
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Electric HVAC on 100 amp service?


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Originally Posted by DoctorWho View Post
Quite sure, have 2 meters outside, get 2 bills!

One meter drops into a 100A breaker panel, the other drops into a beefy fuse box with two 100A fuses, one for each leg I guess.

Any ideas why the guy that did all of this would put a fuse box in for one floor? It's not really old or anything, all of it was done in the mid-1980's! Thankfully he removed all the old knob & tube!
I would look at cancelling one service and upgrading the other to 200 or even higher if you can. Right now you are paying 2x all the other little fees they add on, so it's costing you more.

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