Furnace question

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Anybody happen to know how much initial startup amperage is used for a furnace just coming on, starting its vent motor, and running the glow starter for a gas furnace? I'm needing to know what a reasonable generator capacity would be without overdoing it. Thanks.
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What you really need to know, is the voltage and amperage of the blower
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On 11/21/2010 6:10 PM, RBM wrote:

Not really. The glow ignitor can draw a few amps from the 120 volts.
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Yes, but your blower motor can be around 10. Bottom line, it all needs to work together, so he really needs the total fla
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You also need to remember the ignitor and the blower fan will NOT be operating at the same time under anything resembling normal application. Also, startup current of the eductor motor and ignition will not happen simultaneously.So, what really matters is normal running current of the eductor fan motor and startup current of the blower. If the blower is a brushless DC motor it will also be soft-start and will not exhibit a large starting current spike.
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May be true on traditional-designed furnaces but on new stuff, the ignitor can run with the blower. Mine does it all the frequently. It's a Goodman propane furnace, with a heat pump and a variable speed blower. When it decides to de-ice the heat pump, the blower will continue to run while firing up the propane. On these things, the best way to know the current accurately is to monitor it over time.
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I have 4400 cheapo generator for emergencies. I feed the entire house with it. Runs 2 gas furnaces, a regular fridge, a bar min fridge, and assorted lights, tv, etc.
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If he has a heat pump then he needs a lot more generator.
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On 11/21/2010 6:06 PM, Michael B wrote:

Tables like this will help:
http://www.mayberrys.com/honda/generator/html/requirements.htm
My generator 5,500 watts, 7,350 starting watts, handles my furnace, well, refrigerator, freezer, several lights and a TV. Not hooked up are electric water heater, central AC, electric stove and clothes dryer, the big energy hogs.
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Well, what you are describing is what I want to avoid. Typical motor for running one of those is a 10HP unit. If I can do what I need with a 2HP, my fuel will last longer. Run the furnace till the temperature is where I need it, with sweaters, switch it over to the freezer each day, then to the refrigerator and be frugal about opening it, and use candles when necessary. Yeah, I know a refrigerator has a high startup surge. But a lot of the stuff can be in the freezer for a while.
The furnace says it has a total input of 6.8 amps. But I'm needing to know if the glow ignitor has needs that would transiently exceed that. Because if it doesn't, I could run it on a single kilowatt generator. Bet I could run my freezer on a lot less.
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wrote:

Well, what you are describing is what I want to avoid. Typical motor for running one of those is a 10HP unit. If I can do what I need with a 2HP, my fuel will last longer. Run the furnace till the temperature is where I need it, with sweaters, switch it over to the freezer each day, then to the refrigerator and be frugal about opening it, and use candles when necessary. Yeah, I know a refrigerator has a high startup surge. But a lot of the stuff can be in the freezer for a while.
The furnace says it has a total input of 6.8 amps. But I'm needing to know if the glow ignitor has needs that would transiently exceed that. Because if it doesn't, I could run it on a single kilowatt generator. Bet I could run my freezer on a lot less.
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On 11/22/2010 6:33 AM, RBM wrote:

Neighbor across the street has generator half the size of mine and gets by but said if he had to do it over, he would have gotten larger one. Depends what your needs/wants are.
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On 11/21/2010 10:53 PM, Michael B wrote:

are you planning on some major outage, or just living in the sticks without service?
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On Mon, 22 Nov 2010 08:10:11 -0500, "Stormin Mormon"

An old ONAN will do the job too. I don't know how many hundred hours are on my old beast - it was used as a construction site generator for over 20 years and it still runs great. A bugger to start though with just a rope pull - not even a recoil!!
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On 11/23/2010 10:25 AM, Stormin Mormon wrote:

I got rid of my Coleman 4KW which was quirky. Regulation was poor. When a fridge or the like would start, it would drastically change speed and thus voltage and frequency. I tried a whole bunch of stuff and nothing helped. When it was new, it was very hard to start, but after some adjustment and cleaning of the carb, it started easily. But I could never get it to regulate better. So, now for power outages, we use the Onan 4KW in the motor home, which is parked 10' from the house. It is hooked up right now to the generator panel and can by switched on at moment's notice. It is far better regulated, starts with the touch of a button and is pretty quiet. I think it's 2 cylinders because is runs sooooo smoothly. I've always heard Onans are great and this one is not not an exception. That said, I had a 7KW Onan in a mobile TV truck which was horrible. It was repaired multiple times by the installing company and by Onan and no one could make it reliable. It bounced around in speed, and thus frequency and voltage, whenever it felt like ... nothing starting, etc. It's now a anchor weight in the TV truck replaced by an Auragen belted off the V8. This works very well and as it has an inverter, it is dead on. Of course you pay to run the V8. And, if the belt breaks, as it did a few weeks ago, you have no power.
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You get what you pay for. And most onans are pretty well built. I can't complaint about my el cheapo 4400. It works fine. When the microwave gets used it does take a fraction of a second to bring the rpm back up but I can be watching tv when the microwave gets started and it doesn't disrupt the picture. The lights dim for a tiny bit but I figure it's not a big deal. I don't really notice the furnace fans kicking on though, only the microwave.
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wrote:

Onan is owned by Cummins now. Back when mine was built it was a Stude.
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On Tue, 23 Nov 2010 10:25:21 -0500, "Stormin Mormon"

I've started lots of engines that way. even had one miserable 2 stroke weed-eater that would not start, no matter how hard I pulled - had lot's of spark and compression, and seemingly lots of fuel - so I chucked it in my Myford lathe and wound it up. After about a minute it fired up - I let it run in the lathe for another minute or two, then killed both the lathe and engine, removed the engine from the lathe, and it started on one pull. Never had another problem with it all season - then I got rid of the stinky thing.
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What size blower. Condition and age can make a difference if the motor is worn. Get a clamp on amp meter and test yours, mine takes about 350 running and 700 startup, that is when it was new.
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Michael B wrote:

I think the total load is supposed to be on the furnace manufacturer's tag. You can just use that without going through any calculations of the furnace's individual components. I was about half listening at my last code class when the subject came up.
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