I have a 3 year old hot water furnace. Natural gas fires a boiler and the
water is circulated around the house with a small motor with pump. We are
having more and more power outages here and winter has started.
So here is the question. Is the following a problem. What I would like to do
is get a small generator. When the local 120 V power goes out, I'd like to
disconnect the furnace AC from the house power and plug it into the
generator. I figure a 2 Kw generator ought to do it. Of course the generator
would be kept outside so I don't gas myself and family.
Is there a problem with this?
The typical circulator pump and boiler control electrics may consume even
less power than you think. Mine in Alaska, using a Grundfos pump, ran easily
on the smallest portable Honda generator. I know of people who ran theirs
from inverters and truck batteries in a pinch. Otherwise, no problem at all
as long as you have an absolutely positive disconnect mechanism -- I simply
added a cord and plug to my boiler so that unplugging it from the dead wall
socket and plugging it into the extension cord to the generator made
How long are the power outages? It may be possible to run a small
circulation pump, boiler controls, etc. on a UPS for quite a while, but I
haven't investigated the details. An electrician may be able to wire a UPS
into the circuit. This might be less costly than a generator and has the
advantage of requiring no manual intervention.
The problem with a Ups is it has to be big enough to handle surges of
400% of load for the motors, The cost then puts it in the range of a
quality generator , Which will run as long as you have gas and be more
Boiler circulator- pumps typically take 150 to 400 watts for large
residences ,boilers 100 to maybe 500 watt. Check your load first .
You can do what you suggest but in generators you get what you pay for.
Cheap unregulated voltage units can swing 45 volts or more from no
load to full load. And HZ swings to. Many motors wont start unless
60Hz is there. Electronics can be ruined also. Cheap units are really
for outdoors work, saws etc. Honda is expensive but the electronics are
superior to ALL other small units. And the motors are tops. A 300 $
6 circut transfer kit from Generac at Lowes is the way to go, its a
complete system. Transfer panels make generator use safe . Dont let
the generator run out of gas that can damage the Capacitators on your
boiler motor , if it has any , and other motors, Fridge etc.
I think you've got a good idea. The challenge will be to keep enough
gasoline on hand to be useful. But, what the heck. If it gets you through
several days, that's better than you had before.
I've used my little 2200 watt generator more than once for people. Furnaces
are supposed to have a disconnect box. You pull it apart, and take an old
appliance cord off a junk washing machine or microwave or whatever. Wire it
to the furnace wires with wirenuts, and plug into the extension cord you ran
in from the generator.
If you reread the entire thread you will see that what is being talked
about is replacing the disconnect switch with a receptacle and wiring
the heating plant to a cord and plug. That provides an absolute
disconnect between the homes wiring and the heating plant. The cord cap
cannot be plugged into two places at once so there is no risk of back
The reason so many of these discussions generate more heat then light is
that so many of us are prepared to assume the worst about another
While reading the original message, I would say your interpretation is
the most likely, but I don't believe it is all that clear. Given the
possible consequences of an error, I believe the advice given was warranted.
Ok, the replies sound supportive. I can get into the disconnect box at the
furnace to wire in. Also, there is a switch to cut off from the main above
the furnace already. I don't need to power much more that the furnace. I
don't mind sleeping in the dark or using candles, oil lamps for moderate
light. The fridge can take care of itself as long as I keep my hands off the
door. I have an outdoor gas grill if I need to cook a meal or two (wife
wants only electric stoves -- bummer). So dealing with the furnace was my
Thanks for all that replied.
"Joseph Meehan" < email@example.com> wrote in message
You need to use a switch designed for this use. It needs to provide
100% lockout from the main power supply or 100% lockout of the backup power
supply so there is no way you, or anyone else, can have both on at the same
I don't know if there is anything available designed for a single point
application like yours. Most seem to be for whole house supplies.
Note: this is a real safety issue all the way around and in many if not
all areas is required. This part of the process is important enough, and
easy enough to screw up, that I suggest hiring a professional to do the
One method would be to essentially put a short line cord on the
furnace which would then be plugged into a standard outlet. I
don't know if this is code, however, it would prevent the
problem mentioned. With this, you can "unplug" the furnace when
the power goes out and plug it into an extenion cord which goes
outside to the generator.
Joseph Meehan wrote:
If he converts his heating plant electric supply to cord and plug
supplied he does not need a switch. A plug cannot be in two different
receptacles at the same time so the positive transfer function is taken
care of. It may be a technical violation of the NEC to cord and plug
supply a heating plant but it does not create any real hazard.
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