In brief, is it OK for a gas furnace to run off a GFI circuit?
We have a gas furnace that's about 20 years old in the basement. (It
also has a more recent central A/C unit coil on it.) The furnace is
on a 15 amp circuit. The cable to the furnace runs through a junction
box that has a duplex outlet. (The only things on this circuit are
the furnace and this outlet.) While it is grandfathered under the
local electrical code, code now calls for a GFI outlet (or circuit)
and we are installing one.
Is it OK to run the furnace _through_ the GFI outlet or should we
bypass it? I know that some things don't play well with GFI circuits,
such as some fluorescent lamps. What about gas furnaces? Thanks. -
Thanks for the reply. Yes, we can "wire it before", as you say.
However, since the furnace is all metal and sitting on a concrete
floor, we thought that running the furnace _through_ the GFIC would
provide some safety factor in case an internal short happens in the
furnace. In other words, if there would be no problem having the
furnace run on the GFIC, we would prefer to do it that way. Thanks. -
I think you're doing it the right way.
Wire it to a GFI.
Hell, for that matter, wire it through a Arc Fault breaker too.
That should make you doubley safe.
Maybe a surge protector too.
Use sheilded cable low voltage wiring also with a current balanced
Oh........the mind wobbles.
In light of your suggested safety steps, do you think maybe we should
go even further and skip electricity entirely, switching to a pile of
wood and lighter fluid, and for ignition maybe a road flare will do
the trick? We figure a sledge should be able to open a big enough
hole in the brick wall to get rid of those pesky noxious combustion
gases, or shouldn't we worry about those - too wobbly?
It is not a surprise that some of you experts think that there is no
need for this, and maybe there isn't. The question was whether there
would be a problem with the mid-1980s circuits of a furnace
conflicting with on a gfi circuit. Thanks. - Jesse
Ok, if you really need it spelled out grade school style for
As a hvac expert, I wouldnt dare mess with a GFI on a furnace. Its
just totally unnecessary. No electrical code Im aware of specifies
something like what you want to do. Those damn things trip easily
enough, sometimes without even a problem to trace. As with most
heating and AC problems.....A/C's dont break down when its 70 degrees
out and neither do furnaces. Take a guess when that GFI furnace will
Yep, you guessed it. On a Sat night while you are out of town for the
week and its 5 degrees outside. Guess what kind of igloo you will come
Would there be a conflict? Most likely not but many new furnaces with
all their electrical circuitry can be very finiky......especially when
it comes to grounding and reversed polarity.
Be a pioneer and go ahead and do it. What have you got to lose?
We probably wouldnt have modern day flight if it werent for pioneers
like the Wright brothers. Maybe we wouldnt even have electricity
unless Ben Franklin werent ballzy enough to go fly a kite in an
electrical storm. (Ok, I think he was just retarded to pull a stunt
There, does that answer make you feel all warm and fuzzy inside or did
you really just piss your pants? :-)
Im sure you've heard of the saying, "You can't judge a book by its
The name is of course not Bubba but I certainly am astounded at a few
of the village idiots it tends to attract. It makes me feel "special"
So special in fact that Im picturing CJT out in the middle of the
highway right now in his diaper licking that window.
And, that is the "perfect" situation. You've got no way to access anything
live, and the metallic outer case is bonded to a grounding conductor. It's
the same situation as with a refrigerator plugged into it's outlet next to a
sink: Just have your electrician talk with your HVAC guy, and they'll work
The fact that you don't have a good understanding of the application and
function of a GFCI means that you probably shouldn't be playing electrician
/ furnace installer. "In case an internal short happens in the furnace"
means that either you'll have a line to grounded conductor (neutral) current
flow which will trip a properly sized protection device (breaker / fuse), or
you'll have a line to grounding conductor ("since the furnace is all metal"
("sitting on a concrete floor" really has no bearing on anything) current
flow which will trip a properly sized protection device (breaker / fuse).
From NFPA 70:
550.13 (B) Ground-Fault Circuit Interrupters (GFCI). All 125-volt,
single-phase, 15- and 20-ampere receptacle outlets installed outdoors, in
compartments accessible from outside the unit, or in bathrooms, including
receptacles in luminaires (light fixtures), shall have GFCI protection for
personnel. GFCI protection for personnel shall be provided for receptacle
outlets serving countertops in kitchens, and receptacle outlets located
within 1.8 m (6 ft) of a wet bar sink.
Exception: Receptacles installed for appliances in dedicated spaces, such as
for dishwashers, disposals, refrigerators, freezers, and laundry equipment.
Thank you for the info. And, you _may_ be right. Or, not. A few
things. A licensed installer for the furnace (a swap for an
oil/radiator system) installed the electrical box with a furnace
cutoff switch and an outlet. At the time, that was the only outlet in
the basement. The outlet was 2 pronged w/o a ground. Since that
outlet is sometimes used when servicing the furnace - A/C system, we
thought that it at least should be grounded.
(BTW, when another licensed HVAC person installed a humidifier on our
central system a few years ago, he plugged the humidifier into this
outlet - after cutting off the grounding prong from the humidifier's
power cord. I don't know if the grounding prong is essential, but I
think that someone thought it was.)
As for "in case a short happens in the furnace", this concern came up
because about a week ago there was s sludge backup in the A/C
condensate drain tube and that caused water to back up and then flow
down over the furnace's circuit board (including its connection to the
120v line) and create a puddle in which the furnace was sitting. And,
I discovered this by chance when I went down to the basement barefoot
to get something and noticed that I was standing in that same puddle.
This situation brought to mind a story in the news within the last few
years (from somewhere in the US) about someone who was electrocuted by
a window A/C unit. As I recall the story, the unit created a puddle
on a concrete slab and the person was standing on the slab and in the
puddle when somehow a short from the A/C unit zapped the guy and
killed him. A breaker does not protect people in that kind of
situation - and, as I understand it, that is what a GFI device is for:
As long as you only draw 15amps from a 15amp circuit, if the current
is going from your panel through your body and then to ground the
breaker won't trip but a GFI breaker/outlet will trip. Now, the A/C
story may be completely different from what might ever occur with a
furnace in a basement, but to this mere civilian there are some
Overall, those posting here about the GFI tripping for no reason on a
freezing weekend when we are away - and they do trip mysteriously
sometimes - make a good point.
Again, thanks to you and to all of the others who took the time to
make suggestions. - Jesse
There is no "may be right" about ANYTHING I wrote. "Or, not" does not enter
into my post. Go fuck yourself.
He probably shouldn't have done that. That was something to ask back then.
It is. If the furnace is properly grounded, it does not matter if the thing
is full of water. There will be no potential between the water and the
That's not what a GFCI is supposed to be used for. In the case of the window
AC plugged into what was probably a non-grounded outlet, a GFCI would have
saved his ass. And, application of a GFCI in a non-grounding application IS
spelled out in the NEC.
Electrical code wants the furnace on a dedicated circuit serving no
other load (other than auxiliary equipment to the furnace like an air
cleaner or humidifer), so technically that outlet should not be on that
circuit at all. If you really want to keep it for whatever reason,
however, then it would be better to not run the furnace through the
GFCI. There is no real safety advantage to it for a furnace and there's
the risk of nuisance tripping.
Robert Hancock Saskatoon, SK, Canada
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