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Post in 'DIY and General non-hearth advice' started by velvetfoot, Dec 23, 2010.
Would a 7 amp generator do it?
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According to this chart, 1500 watts. Don't know how that translates to amps
volts x amps = watts. 120v x ??? = 1500 watts. Divide it out and you get 12.5 amps if I did that right. Nope, need a little more...
You will have a few things to add up for the system to be operational.
#1) Boiler burner motor.
#2) Your zone valves/transformer/relay loads if you have any. (they are minimal but add up if there is a significant amount)
#3) any circulators/pumps required to move your heating medium that are on your system.
Each device will have its own individual rating.
All must need to be considered to have heat.
Thanks very much.
I have a vague recollection from HS physics of a formula, WEAV. Watts = Amps X Volts
Don't hold me to it. I'll leave it to more knowledgeable posters
I sort of measured it last night. I have a whole house power monitor and it looks like it takes about 270 watts steady state, with oil gun firing and one circulator. So, a 7 amp generator ought to do it, I would think, even with the startup.
My oil burner runs fine served by a 15A breaker so I'd guess that the draw is quite a bit less than that.
The pumps are minimal. I forget the math but it wasn't that much, around .7amps. Relays, switches and gizmos are in the milleamp range, which I guess can add up but figure an amp for everything. You main draw is your burner, which (depends on the brand) will draw a starting wattage of around 7-10 amps, then settle down to between 2-5 amps. Your whole system is less than 10 steady amps, and probably closer to 5.
What you may want to watch out for is if your boiler has an electronic control, it will need a better quality juice than you might think. Last year I had a tekmar 260 that wouldn't work with my genset, because the control would fire the burner, and the induction load of that motor would drag the voltage below the 5% threshold of the control. The control would konk out, shut off the burner, then come back up and start it all over again.
That's interesting about the Tekmar, because I have a 256 outdoor reset.
I put a clamp on meter earlier and came up with ~4.3 amps on startup, total.
I'll try to give it a whirl tomorrow.
Its not the amperage draw but the initial voltage drop cased by the burner's motor that will cause the control to cut out. You're generator will more than likely chug through it but the control may have a hard time with it. I was in the middle of wiring mine with a plug and I was going to feed it from a small UPS , but I ended up replacing the whole boiler
I thought about being able to run it with my generator... but it is hard wired, and I am not able to plug the generator into the house, so thats no-go for me. No big deal, still can run the fireplace!
What some people have done is to "unhardwire" the furnace by putting a plug and receptacle in the line to the furnace. Then they can plug the furnace into an extension cord from the generator. I don't know if that violates any codes, I doubt it, but it works for them.
FWIW, I run an oil furnace, 3 zones, and one circulator pump on a 3500 watt generator. It does grunt when the burner motor starts, but runs it all easily after that. The genny will also run our 115v well pump at the same time, so we can take showers, etc.
The furnace has an older control on it with a few transistors in it, and it doesn't seem to mind the power dip or dirty generator power.
I believe in the last year the OP has done just that--both unhardwired his boiler AND run it on a nom 7 amp genny.
We have a Tekmar 260 for a little over a year now. It runs great with our Buderus G115WS/4 Cast Iron Oil FHW Boiler that is a Triple Pass, Cold start boiler
What Make and Model boiler do you have?