# How big of a generator might be needed to run a natural gas furnace?



## Oggie (May 29, 2003)

Given that the only power usually required is to run the fan and perhaps some of the controls, would it be feasible to temporarily run a natural gas furnace on a portable generator?


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## newfieannie (Dec 24, 2006)

Oggie said:


> Given that the only power usually required is to run the fan and perhaps some of the controls, would it be feasible to temporarily run a natural gas furnace on a portable generator?


I'd like to know this too Oggie. this is my first time with natural gas. I'm still trying to find out if the fireplace will work if the power goes off...Georgia.


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## georgec (Jul 9, 2007)

I natural gas or propane furnace would easily run on a larger portable generator. Just look to say the size of the breaker that supplies the furnace, multiply that by 220 and you will have the size generator you will need (very approximate).


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## Michael Kawalek (Jun 21, 2007)

My natural gas furnace uses a pigtail style electric heating element to light the gas. I would guess it requires about 500 watts at startup then goes out after the gas is flaming. Then, when the fan motor kicks in it probubly needs about another 500 watts for starting. I'd say you'd need at least 1000 watts total for startup if both are on at the same time.
Michael


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## palani (Jun 12, 2005)

A couple of 12 volt batteries and a 1 kw inverter should handle it without all the hassle of a generator. This would probably be good for a couple of hours anyway.

Run the inverter off the truck batteries.


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## texican (Oct 4, 2003)

Want some cheap insurance? Go ahead and get a genny, if you really want to... but to be on the safe side, have an old fashioned gas heater, you know the kind grandma had, with little ceramic grates. Have a couple of outlets plumbed into your house, or have one of those long propane 'extension hoses' like they use for camping, so you can, when things go 'south', hook up a heater into a wall gas outlet, or to the propane tank outside the window.

If you have an extended period with no electricity, will you have enough gas on hand to keep the genny going during that time?

Simpler is better, when it comes to heating.


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## rambler (Jan 20, 2004)

There is a plate on your furnace someplace that says what it needs for electricity - volts (likely 120) and amps.

This will tell you what you need to know.

Likely any 5 hp genny or bigger will run it just fine. Smaller might too, but perhaps you want a light bulb or water pump to run? 5-9 hp gennies seem to be the common starter units.

--->Paul


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## PyroDon (Jul 30, 2006)

Well you can hear the load come on our 5250 watt genny each time the furnace fan starts . 
I personally wouldnt go any smaller than 5000 watts and would be more comfortable with 10,000 watts (which is what I'll be looking for soon) 
Lifes much simpler with a few extra watts then you can run the frige and lights as well as the furnace. I put a 220 plug tied into our main breaker box that plugs right into our genny. this allows me to simply throw the main disconnect and back feed through a 220 breaker to supply the entire house


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## rambler (Jan 20, 2004)

PyroDon said:


> I put a 220 plug tied into our main breaker box that plugs right into our genny. this allows me to simply throw the main disconnect and back feed through a 220 breaker to supply the entire house



(Edit: Rereading your message, not sure how you meant this? Did you put in a special switch that only connects the plug when the main is disconnected - else you would have hot exposed prongs all the time? All my comment below is then totally misdirected & - never mind, my misunderstanding.)


Now we'll start _that_ discussion again. 

To code, and to your electric supplier, and to your insurance company, that is a big no-no because _if_ you forget to trip the main, it has a _possibility_ of causing problems. It does make the lineman's life a lot harder, because he doesn't know if you are backfeeding into a 'dead' line.

Many do it this way anyhow, but probably not such a good idea to suggest it out loud.

There are special switches that interconnect a main switch to the generator power in switch & do this connection 'to code'. They probably cost $200-400 so yea, it's some money.

Not trying to start an argument Don, just the other side of the coin should probably be mentioned too.

--->Paul


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## OkieDavid (Jan 15, 2007)

Rambler,
Good points all!!! Scares the crap out of every lineman and trust me, they drive through looking for lights/generators. Everytime our power is out, they "swing by" and want to see if we need our meter resealed....Actually it's just a ploy to see how I'm feeding the house. If there's just a few orange extension cords run through a window that are plugged into the 120v side of the generator they don't even get out. When they see my 8 gauge 220v extension cord hooked into the generator and running through the window, they want to SEE the connections. I also agree with your concerns about posting "out loud"....someone knowledgeable about the dangers (and therefore following appropriate safety measures) already knows this stuff but an inexperienced homesteader who sees information on making a suicide cord (double male plug extension cord) and FORGETS a single step in the process of backfeeding a house can injure or kill someone. Also, we all know that even in times of emergency/survival we must always follow the local codes and insurance requirements.....  Word to the would be "home" electrical utility providers- If you aren't familiar with the terms; backfeeding, step up transformer, safe clearances and step current, ASK someone knowledgeable to assist you.


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## PyroDon (Jul 30, 2006)

rambler said:


> (Edit: Rereading your message, not sure how you meant this? Did you put in a special switch that only connects the plug when the main is disconnected - else you would have hot exposed prongs all the time? All my comment below is then totally misdirected & - never mind, my misunderstanding.)
> 
> 
> Now we'll start _that_ discussion again.
> ...


well paul Im not sure if its to code or not .
I dont see it as an argument you make a very valid safety point and I apologize if I did not make it clear to disconnect the house from the main line first . You also have to be very careful to keep the polarity correct when making such a cord or you will take the chance of damaging appliences and the generator. 
what I did was made a double male ended extension cord out of 4 conductor 8 guage wire . turned off the main breaker coming into the house and plugged the cord into the window airconditioner plug ( a dryer plug would work as well ) being that we also have an electric water heart that breaker had to be switched off as well . 
So in effect the house was completely disconnected from the mainline .
I agree you have to be absolutely sure the house is disconnected from the power lines .
The switch you speak of is in effect nothing more than a main disconnect breaker connected to a generator breaker or in very simple terms a triple post double throw Having one installed is quite expensive and if you get an auto switch they cost nearly as much as a generator its self .

To Oggies question a 1000watt genny is not near enough to run the furnace. You have to take the start up watts of the blower into account as well as the running watts . Our furnace is on a 20 amp breaker which means the start up wattage is some where around 2400 watts. meaning the min generator you would need in a best case would be 2500watts with a 3000 watts surge . Now you have to understand that a 2500 watt genny is the total wattage out put , most have two plugs which means your only getting 1250 watts per plug (not enough for a furnace ) .You will need a min of a 5000 watt genny to power your furnace and will have 2500watts you can use to power something else such as lights of a fridge. 
Your standard fridge will require around 1500 watts to start the compressor .


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## marvella (Oct 12, 2003)

far easier and cheaper to just install one of those wall mounted ventless gas heaters in the main room. just keep the pilot lit thru the winter and if the elecric goes out, just turn the knob and it comes on. no sense in trying to heat the whole house.


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## Oxankle (Jun 20, 2003)

I'm with Marvella. 

Those double-ended male cords have killed too many linemen. I would not want the responsibility for that. Sooner or later SOMEONE would forget that the main breaker had to be pulled and the transformer would be loaded when a workman touched the line.

The wall heaters Marvella talks about are made both in vented and non-vented styles. I prefer the vented; it is so easy to run a small vent pipe up through the wall and out the roof. They are even made with a small fan, I believe. The one I used heated a room 20 x 24 well enough here in OK. 

In an emergency all that is needed is enough heat to be comfortable with clothes on and to keep the pipes in the house from freezing. That does not take a lot of heat. If you have a small generator for your fan, TV and radio, an electric skillet or wok, coffee pot and fridge you are good to go. Oh, don't forget to run a cord to the electric blanket at night. 

I have a 5500 watt Troybilt genset. Ran it for several days last winter when we were iced in and it did all the above plus my wife's oxygen concentrator. Did not have a wall heater then, but had a fireplace with a blower. Kept us toasty. 

Ox


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## hunter63 (Jan 4, 2005)

This was an interesting thread, so I checked the plate on the inside of my American Standard NG forced air furnace, found that it's rated at 8.5 amps, om a 15 amp breaker.
So if you use I (amps) X E(volts)= w(watts) comes out to;
8.5 amps X 117vac = 994.5 watts ( I would think that it would [email protected] blower start up), and as the Genny is 5500 watts, it should be plenty.
Never really gave it much though till now, thanks.


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## Ross (May 9, 2002)

The biggest draw will be your blower fan so if the belt is too tight or the bushings shot, or something is drawing down the motor the most you'll draw is 30 amps for start up. It'd be unusual and you'll be replacing that motor soon but it's about the highest draw I've ever seen. 30 amps @120v is 3600 watts. Go big or go home 5000 would be reliable running in the worst conditions.


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## mdharris68 (Sep 28, 2006)

Interesting discussion, as we have been in one of the worst ice storms/power interuption for quite a while. I have either hooked up or given advice about hooking up generators to furnaces about 40 times in the last 5 days. I learn something new every day. First I would say that a one kilowatt (1000 watt)generator should run a typical furnace. Previous posts have given good figures on the energy needed. 

What I have seen as the most important things to consider when hooking up a genny to your furnace, (if it is new enough to have a circuit board)

1. Be sure to keep the original ground from the main breaker panel to your furnace.

2. It may require power produced at 60HZ.

3. Polarity in your wires (extension cords) can make the difference on some of the furnaces.

One problem I have seen is the customer would hook up an old generator to thier furnace and it would work for say 24 hours. Now they have had time to go and buy another generator and let thier kids or neighbor use the old one while they hook up the new one. Now the new genny will not work on thier furnace. I think that these new generators have a cheap voltage regulator that caused wide swings in the actual delivered voltage which these newer furnaces are more able to detect and lock out and not run. 

One thing to be aware of.........

If you have a furnace with a variable speed blower, make sure you have a very reliable, clean sine wave with 60 hz coming into your furnace. A surge protector in line to one of these may end up saving you 500$ or more for a new variable speed motor.

The older furnaces should run with little or no problems. 

One thing that I have realized this last week is I am real glad that my lights only flickered twice while thousands around me are looking for thier power to return sometime around Christmas or thereafter.


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## empofuniv (Oct 14, 2005)

I sent a link to this thread to my SIL in OKC this morning because she is trying to decide what size/type generator she needs. She is a single woman who is pretty dang self sufficient, but she needs some advice on this.

I hope it is OK for me to post her question for her, her power came back on yesterday and she doesn't know how long it will be on. The block next to her has lost their power again.

Her question: 
~~~~~~~~~~~~~~~~~~~~

Thanks so much for the link. I read it carefully and even with the knowledge I have been slowly accumulating in my research, I still am a little confused.

Would it be possible for you to post a question for me since I am not a registered member? If you think it inappropriate or poorly written, please feel free to edit. If you prefer not to post it, that's fine. I'm just looking for advice to make the best purchase possible. The unit I am considering is $1299 so I am understandably leery.

Here's what I would like you to post:

I have been getting advice from different vendors until my head spins. Folks on this thread have suggested I will need a 5000 watt genny to run my furnace but I have received conflicting info from my local dealers.

I have been looking at a Yamaha EF2400iS. Several vendors have assured me that this genny will power my 1/3 hp natural gas (110v blower says maximum input 12.0 amps) heating unit, plus my refrigerator/freezer unit, a television, a light or two as well as my desktop computer. Home based business makes it imperative that I can use my computer so I am only looking at generators with an inverter.

I have absolutely no experience in this area and looking for advice. Do you think these guys know what they are talking about or are just going for a sale? 

Any input or advice would be greatly appreciated.
~~~~~~~~~~~~~~~~~~~~~

I'll pass along any advice, tips, pointers or suggestions to her right away.

Thanks for being there, you are all appreciated.

Pamela


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## mdharris68 (Sep 28, 2006)

empofuniv said:


> I sent a link to this thread to my SIL in OKC this morning because she is trying to decide what size/type generator she needs. She is a single woman who is pretty dang self sufficient, but she needs some advice on this.
> 
> I hope it is OK for me to post her question for her, her power came back on yesterday and she doesn't know how long it will be on. The block next to her has lost their power again.
> 
> ...


Ask your SIL if she knows anyone in the telephone business. They all have guys who do nothing but work on generators and peripheral generation equipment, and allthough they are working on generators usually much larger, the knowledge base is what she's looking for. An electrical engineer may be another option for her to tap into the knowledge base. Research, research, research is the key.


If I were running a homebased business that required a computer to be running, I would consider one of those battery backup systems that have surge protection. Also, there are numerous generators out there that can run a whole house using natural gas and or propane for fuel. 


The furnace should pull about 8 amps and use about 960 watts on start-up and ramp down to 3-4 amps or about 360-480 watts while running. Hope this helps a little.


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## empofuniv (Oct 14, 2005)

If SIL has power she will be monitoring this thread, if she doesn't have she'll contact us and I'll pass along answers/suggestions.

And my children wonder why I don't live in OK anymore!

Pamela


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## rambler (Jan 20, 2004)

As to the interlink switch of plugging in a generator into a dedicated 230v receptical, here is a device that may help a person meet NEC code for cheaper than a regular transfer switch. I'm no electrician, so do your own research. 

http://www.interlockkit.com/

--->Paul


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## tiogacounty (Oct 27, 2005)

rambler said:


> As to the interlink switch of plugging in a generator into a dedicated 230v receptical, here is a device that may help a person meet NEC code for cheaper than a regular transfer switch. I'm no electrician, so do your own research.
> 
> http://www.interlockkit.com/
> 
> --->Paul


Rambler, these devices are pretty clever. Sq-D has had one for some of their residential panels for a few years now. I have used the double male 30 amp cord jumper for years. That said, they are illegal, and in the wrong hands, perfectly capable of killing the user or a lineman. The flip side of the danger of killing a lineman is that it is possible to have the power company burn your house to the ground once the power is restored. The situation happens when the main breaker in the house panel is left on while the grid is down. Once the grid comes back on and the generator is still operating, the house is fed from two sources. I saw an article about one of the recent hurricanes in FL. Where a power company rep. explained that they had started fires in six homes that were operating illegally installed generators. A neighbor of mine had visible little "bolts of lightning" shooting from his receptacles as the power company re-energized the grid. Repairing the house was a pretty expensive insurance claim, and the company really could of left him hang, being that he was the idiot that caused the problem in the first place.


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## BillHoo (Mar 16, 2005)

Oggie said:


> Given that the only power usually required is to run the fan and perhaps some of the controls, would it be feasible to temporarily run a natural gas furnace on a portable generator?


Get a small steam engine and have some of the hot water from the furnace power the steam engine which in turn will rotate a fan.

Here's one on eBay for $51 (at time of the auction)

http://cgi.ebay.com/Dirty-and-Ugly-...0189920167QQihZ019QQcategoryZ30QQcmdZViewItem


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## empofuniv (Oct 14, 2005)

Thanks to all you good folks who shared your knowledge about generators.

My SIL has made her decision and I thought I'd share it with y'all.

Here are parts of her email:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Well, right now I am in full panic attack and breathing heavily into a brown paper bag as I write. LOL 

I jumped into the deep end and ordered a Honda EU2000i. Purchases this large, especially when I have to charge them on a credit card, make me so uneasy. I just keep telling myself that it's not like this is never going to happen again.

The salesman assures me that this should provide the power I need. Possibly might have to take turns between the refrigerator and the furnace as it might not handle the surge when they both kick on at once, but everything I have read says that I would really only need to run the fridge about an hour or so a day to keep it cold enough.

The price was much more reasonable than any others I had found - $880 with free shipping and no tax. I had found a couple here locally, the cheapest was $999 plus $88 tax. So this is just over $200 in savings. Ships out tomorrow and should be here by Tue or Wed.

All of the salesmen I talked to here, told me I didn't need the inverter models. I think they just wanted to move as many units out the door as possible and really had no knowledge about what they were selling. 

I know this probably sounds pretty silly to you all, but trying to buy something I had absolutely no knowledge of was extremely intimidating for me. Being alone and cold - without electricity and other everyday conveniences really affects your judgment. It was so helpful just to have someone which I could bounce ideas off and get their feedback. I have to say, that is probably what I have found to be the most difficult aspect of living alone.
~~~~~~~~~~~~~~~~~~~~~~~~~~
Thanks again folks, you helped her reach a decision and broaden her (and mine!) knowledge base.

And if you know of where she could have gotten the same item cheaper and faster...pls don't tell us!!

Pamela


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## LINEMANPB (Feb 22, 2021)

OkieDavid said:


> Rambler,
> Good points all!!! Scares the crap out of every lineman and trust me, they drive through looking for lights/generators. Everytime our power is out, they "swing by" and want to see if we need our meter resealed....Actually it's just a ploy to see how I'm feeding the house. If there's just a few orange extension cords run through a window that are plugged into the 120v side of the generator they don't even get out. When they see my 8 gauge 220v extension cord hooked into the generator and running through the window, they want to SEE the connections. I also agree with your concerns about posting "out loud"....someone knowledgeable about the dangers (and therefore following appropriate safety measures) already knows this stuff but an inexperienced homesteader who sees information on making a suicide cord (double male plug extension cord) and FORGETS a single step in the process of backfeeding a house can injure or kill someone. Also, we all know that even in times of emergency/survival we must always follow the local codes and insurance requirements.....  Word to the would be "home" electrical utility providers- If you aren't familiar with the terms; backfeeding, step up transformer, safe clearances and step current, ASK someone knowledgeable to assist you.


I am that lineman, but I will stop at your house and see for myself that it is correctly connected. In my business we don't just go by opening a breaker, we get a visual opening and you can't do that by flicking your breaker to the off position (you can't see inside to make sure it broke the connection). We pull that meter and now there is a visible opening.


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## muleskinner2 (Oct 7, 2007)

marvella said:


> far easier and cheaper to just install one of those wall mounted ventless gas heaters in the main room. just keep the pilot lit thru the winter and if the elecric goes out, just turn the knob and it comes on. no sense in trying to heat the whole house.


Unless you can drain the entire plumbing system of all water, you may have to heat the entire house to keep from bursting pipes.


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## Rural Kanuck (Apr 13, 2020)

As a retired electrician (in Canada not that it makes much difference for this discussion) I feel I MUST warn against that 'double ended plug' suggestion eiriier in this thread and any similar suggestion that do not physically disconnect one power source before connecting another AND making it impossible to connect both at the same time. This is how people ket killed! If you are not in a position to install proper (and expensive) generator change over switches the soloution is fairly simple and relativity inexpensive, simply make the item you wish to be able to hook up to the jenny plug in to its usual supply (a gas furnace will just need a simple 110 v plug in most cases) then when power goes down simply unpug the item and plug into a cord going to the genny. Just make sure you use decent cord rated for the load, you can then switch to other loads similarly prepared as required as and when needed ( even a table lamp or trouble light to see what you are doing)

Simple SAFE and inexpensive solution to occasional power failures and the one that this Licensed Electrician uses on the rare occasions that I loose power.
PLEASE do NOT use that double ended cord trick those live plug ends scare the h outa me


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