Powering gas furnace

Old 10-05-10, 03:26 PM
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Powering gas furnace

I have a 3500 watt max portable generator,according to all the charts I have enough power to run it alone with out much else running,the igniter will light but when the blower trys to kick on the electrical switch trips on the generator,why does it do this? I run it from one of the 120volt outlets,does it need to come from the 240 outlet to work?
Old 10-05-10, 03:40 PM
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I run it from one of the 120volt outlets,does it need to come from the 240 outlet to work?
Is the furnace wired to 240v or 120v? How are you connecting the furnace to the generator? Are you using a inlet and transfer switch?
Old 10-05-10, 04:33 PM
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This is interesting, considering most furnace blowers are like 1/3 HP or less.

Is the 3500 a total rating maybe a temporary peak amount?, or can you draw that steady?

And would such a rating, on a generator capable of 240 volts, have it divided up so in actuality, you only get 1750 watts per leg?

And since you are on one 120 volt leg, as you should likely be, coupled with the fact more wattage is necesary to start up at the motor, maybe the combination of these two things is doing it?

Old 10-05-10, 07:07 PM
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This part may open your eyes due most small generators will have two 120 volt coils {AKA circuits } they function the excat the same way as transfomer are.

So with 3500 watt generator and you plug in one of the 120 volt recetpale you will only get 1750 watt each that why the generator breaker will trip.

Only way you can get full 3500 watt rating of the generator is if you have full power option so which it mean they will change the connection on generator stator connections from normal 120/240 volt fashon to full 120 volts in parallel set up so it can able use full load of the generator.

So that one thing you have to look around with it.

Old 10-05-10, 11:18 PM
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Even at 1750 watts it should be able to run the furnace unless you have a really big furnace. 1750 watts is 14.5 amperes and the furnace shouldn't take much more than 12 amperes maximum. If I remember correctly my furnace draws about 8 amperes when lighting and then drops back to about four when the blower is running. The ignitor element in your furnace should have dropped out before the blower starts, if it doesn't it may be a fault in the blower switch assuming your particular furnace uses a thermoswitch rather than a timer to initiate the blower.
Old 10-06-10, 08:40 AM
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I agree that a normal gas furnace should run or less than 1700W with no problem, probably less than 1000W even. Either the breaker on the generator is very sensitive and tripping too soon or the furnace is drawing too much current for some reason. I think you need an amp clamp meter to figure this one out.

Most furnaces do not even have the ignitor and blower on at the same time. The blower comes on at some delay (usually about 20-30 sec) after a successful ignition and the heat exchanger has come up to temp. The ignitor itself is the biggest load at a couple amps and should really only be on about 5 sec before the gas valve opens then shut off right after ignition. That shouldn't be long enough to trip the breaker.
Old 10-06-10, 10:27 AM
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How are you hooking the generator up to your furnace?


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