Battery Powered Furnace

[joesxm3]

My friend told me that he has hooked up a big lithium-iron battery and inverter to his furnace and can run it for 24 hours if the power goes out.

I would like to do this to mine, but figured I would ask a few questions.

I have what I guess is called an oil hot-water boiler system. The furnace heats the water and it goes through the pipes to the rest of the house. The water is moved by these zone pumps that are attached to thermostats and located next to the boiler unit.

I hadn't thought of it before, but it seems that the only need for electricity is to power the zone pumps and thermostats. Maybe there is also some sort of electric sparker to light the oil to start things off. Does this make sense?

He said that he inserted a plug outlet into the wiring so that the can flip the breaker switch for the circuit, run an extension cord from the inverter and provide power to the circuit, to my simple mind "in the backwards direction".

Does the circuit work like you can just feed power in from somewhere instead of from the breaker box? Is there any reason that power hitting the breaker switch from the other side would hurt it?

I realize that you can't just feed power back into the system while you are connected to street power. I have a generator and what I think is called a "transfer switch". It is a thing that I flip that disconnects my breaker box from the street and connects it to the wires that bring in power from the generator. I think what he is doing with the battery is sort of like what the generator wiring does.

I realize that I probably cannot run both the generator and the battery at the same time. Maybe I could if flipping the furnace breaker switch cuts it off from the power coming from the generator, but I probably would only use the battery when the generator was not being used.

From what I can see, the general principle seems like it would work and as long as I am disconnecting from the street it seems like it would be safe. But I wonder if there would be some building codes involved. I realize that building codes might be town-specific.

Anyway, do any of you have thoughts on this idea?

Thanks.

 

[Texas Proud]

My question would be how much did this cost him?


For me, I just installed a whole house generator and now my only worry is that the gas company will not send gas if the electricity goes out...



Last year that did not happen here, but I heard it did in Dallas

 

[Walt34]

You have the basic ideas right, but I would strongly encourage you to hire an electrician to do any of the actual wiring on this. Doing it wrong can feed electricity into the grid during a power failure and lots of bad things can happen, including electrocuting linemen and starting fires.

The transfer switch is the device that disconnects your generator from the grid when the generator is running so evidently you have that part right. Think the idea you're looking for is to have yet a second transfer switch, this one to isolate the generator from the battery/inverter. No reason it can't work I suppose, but what's wrong with using the generator?

 

[Sunset]

People discussed this some time ago, but using a generator.



Same idea, the generator or inverter would supply the power needed to start the furnance and run the fan (or pumps). The system won't take much assuming it a gas furnace.

 

[travelover]

When we discussed this last time, I mentioned that I wired in a plug on my furnace power inlet and plugged it onto the dedicated furnace outlet ilo being hard wired. You'd unplug the furnace from that outlet and plug it into your battery powered inverter.


There was a lot of hand wringing over this, but I think it is quite safe. Alternatively you can wire in a little transfer switch.

 

[joesxm3]

When we discussed this last time, I mentioned that I wired in a plug on my furnace power inlet and plugged it onto the dedicated furnace outlet ilo being hard wired. You'd unplug the furnace from that outlet and plug it into your battery powered inverter.


There was a lot of hand wringing over this, but I think it is quite safe. Alternatively you can wire in a little transfer switch.

That sounds like a good idea. A dedicated plug would make it totally safe unless the battery somehow explodes.

My friend said that the battery costs about $1000, plus the inverter and electrician.

The advantage compared to having to haul my generator out onto the driveway in the middle of a blizzard would be obvious. Having a permanent automatic generator would provide the save convenience. I paid $1400 for the 8kw generator and $800 for the electrician to do the wiring. Maybe it would have been better to just have bitten the bullet and paid the $6000 for the big generator setup back then.

 

[skyking1]

Yes that is how I set up our group B well that serves 4 homes. The genset we have will not run the well and also the pressure pump at the same time. There is a 500 gallon post treatment tank, and then the pressure pump pressurizes the 3 tanks that serve the domestic water.
I wired the wellhouse with proper 240V twist lock plugs, and then made a cord for the genset. The well will fill that 500 gallon tank in a short while, then I can plug in the pressure pump. There is no unsafe condition there.

 

[ERD50]

When we discussed this last time, I mentioned that I wired in a plug on my furnace power inlet and plugged it onto the dedicated furnace outlet ilo being hard wired. You'd unplug the furnace from that outlet and plug it into your battery powered inverter.


There was a lot of hand wringing over this, but I think it is quite safe. Alternatively you can wire in a little transfer switch.

I agree that just adding a cord to the furnace is simple, easy, and perfectly safe (assuming you got the hot/neutral, ground connections right!). In the discussion, there was some question of codes not allowing flexible cords for fixed items like furnaces, I don't recall if any of the reasoning was solid or not. But the transfer switch does eliminate any question, and isn't that expensive.

First step - find out how much current the furnace draws on average, and max. Then you can size the battery and inverter to match. Those pumps and maybe a fuel pump and electronics probably don't draw all that much.

-ERD50

 

[joesxm3]

Well it all sounds good in theory, but the practical application may be a different matter.

I took a look at the furnace and it seems that the guy who installed it back in 1987 made some sort of Rube Goldberg setup.

I have four zones for the living area and one zone for the hot water heater.

The wire coming from the breaker box seems to go into some square box thing that seems to have one of the living area zone pumps wired to it.

The wire goes into another box that has two utility plug outlets and some wires coming out to other parts of the system.

One wire goes to a larger box that has wires to the other three living area zone pumps and what looks to be thermostat wires. Another wire goes to another small box that goes to the water heater zone pump. Then a third wire goes down to the burner unit.

I am guessing that the three boxes connected to the five zone pumps must be some sort of control units that feed power to the zone pumps when the thermostat circuits are triggered. Hard to understand why there was not just one control unit, or at least a four pump control unit for the living area and one for the water heater. He must have been using whatever junk parts he had lying around.

At the time I thought the guy was reputable since he was the friend of a guy I worked with, but years later when my well pump needed to be replaced he raped me to the tune of $2000 more than the fair price, so I guess anything is possible.

Maybe it is time to consider replacing the furnace. If I did, I think I would like to have a hybrid unit that I could either run on oil or burn wood in.

In any case, it will be a good mental exercise to try to figure out what all the parts to the system are and how it is wired. It is amazing how I survived for 35 years in the house being so clueless as to how all the systems operate.

I suppose if I attack the circuit farther back from the furnace, I may be able to just tap in the plug without worrying about the screwy setup closer to the furnace. I definitely will have to get my reliable electrician involved with this one.

 

[OldShooter]

You have the basic ideas right, but I would strongly encourage you to hire an electrician to do any of the actual wiring on this. ...

+1 Your questions and thinking are good but my guess is that you have not done a lot of wiring yourself.

But running the furnace does not give you a livable home. Lighting? Microwave? TV or stereo? Computers?

Also, your run time is limited to the battery capacity. We have had outages of several days both in the city (ice storm) and in the country (wind, thunderstorms).

I would go back to the generator strategy. The odds are you won't actually be having a blizzard every time you need to run the genset. Maybe never. Or step up to a non-automatic generator in an outside doghouse.

 

[mes56]

Definitely electrical code elements apply. If you extend your thought about running the electricity "backwards", one of the things that has to be addressed is not putting electricity back out the lines to your house when the crews are working to repair the outage.

 

[travelover]

In post #1 you said you already have a generator and a transfer switch, so I assume your desire for the battery backup is to avoid running the generator all night.

One option would be to just get a small inverter generator to just supply minimal power. A Honda 2200 watt inverter generator will run all night on a gallon of gas. That would cost about $1100, though there are cheaper knockoffs that would suffice. These inverter generators are very quiet.

 

[joesxm3]

My main concern would be not running the generator during the storm. My second concern would be someone stealing the generator.

The current generator works well, and I do have a wood stove, but it does not evenly distribute the heat.

I got on the idea when my friend told me about his yesterday. He likes playing with batteries. He already has some sort of diesel engine used by the British to run irrigation pumps in india. It has a huge flywheel and goes thunk, thunk and runs for a day on a couple gallons. He has it in his garage with an exhaust pipe out the wall. He hooked it up to power a generator. So he really doesn't need the battery, but I guess he is bored having retired recently.

My house holds the heat pretty well, so I can probably make do with what I have.

 

[skyking1]

Your more complicated hydronic system might be a bit much to figure out simply. A straight up furnace, with a single blower and ignition system is what I think of when setting up direct generator/inverter power to.

 

[skyking1]

My main concern would be not running the generator during the storm. My second concern would be someone stealing the generator.

The current generator works well, and I do have a wood stove, but it does not evenly distribute the heat.

I got on the idea when my friend told me about his yesterday. He likes playing with batteries. He already has some sort of diesel engine used by the British to run irrigation pumps in india. It has a huge flywheel and goes thunk, thunk and runs for a day on a couple gallons. He has it in his garage with an exhaust pipe out the wall. He hooked it up to power a generator. So he really doesn't need the battery, but I guess he is bored having retired recently.

My house holds the heat pretty well, so I can probably make do with what I have.

Lister diesel, most likely.

 

[RetiredAt55.5]

My friend told me that he has hooked up a big lithium-iron battery and inverter to his furnace and can run it for 24 hours if the power goes out.

I would like to do this to mine, but figured I would ask a few questions.

So, what's the plan after 24 hours?

We lost power once for 5 days. The first day wasn't too bad. But then it could progressively worse. And then I started worrying about pipes freezing.

So, some considerations with a battery only solution -

What's the service life of the battery, before you need to replace it?

How long would it take to recharge a fully discharged battery? ( you could run an inverter off your car battery to recharge it, but you'd have to have the engine running and a place to do that safely).

What's the cost of a big battery? (I'm curious how that compares to a small gas generator that is only limited by the amount of gas).

 

[travelover]

My main concern would be not running the generator during the storm. My second concern would be someone stealing the generator............

You could make this work. The biggest obstacle seems to be figuring out how the system is powered so you can attach a single source to power it.

You can buy a hundred amp hour lithium battery, a pure sine inverter and a charger for the battery so you can charge it off the generator if you need to go additional nights. It might be cheaper to buy the small generator and make a weather tight / theft proof place for it to sit and run.

 

[Sunset]

How about just running the generator in the day, when you can see it and protect it and then lock it up at night in the garage.


A house can survive a night without electric power easily, even in Winter.

 

[DayDreaming]

With recent improvements in battery technology, some folks are using batteries instead of a generator to power their house. It's sort of like having solar on your house with battery backup, but without the solar panels. Your batteries are just charged from the grid instead of from solar panels. Maybe you could look into one of these commercial systems like Tesla's Powerwall (and others). Since your furnace wouldn't be running constantly, you could also use it to power lights, fridge, etc, although you'd probably need to be very careful about running the battery down.

Search for 'battery instead of generator' and you'll find a lot:
https://www.cnet.com/home/energy-an...hich-backup-power-source-is-the-best-for-you/

I've been thinking about this myself, because when power goes out, it's usually stormy and I really can't get my portable generator set up until the storm passes. I'm thinking I could last a day on battery power without needing a huge array of batteries, but beyond that it would have be back to generator.

 

[joesxm3]

That's pretty much what I was thinking. Battery just to ride out the storm and generator after that.

That motor in the picture is the one my friend bought. He called me to come see the new toy and then sprung the news that I had to help him take it off the trailer.

 

[DayDreaming]

That's pretty much what I was thinking. Battery just to ride out the storm and generator after that.

I'm also thinking if I do the battery correctly now, then it might be easy to add solar later.

 

[old medic]

First step - find out how much current the furnace draws on average, and max. Then you can size the battery and inverter to match. Those pumps and maybe a fuel pump and electronics probably don't draw all that much.
-ERD50

I would be more concerned it would draw more. you most likely have at least 4 120V pumps,pushing water not air, the burner ignitor and fuel pump. Add a 12 volt transformer for the thermostat and controls on top. If thats all running off one breaker in the panel then your idea could work. Personally would go the generator route.

 

[street]

Like some have noted that you will need to get a total measurement of amperage usage. I would think it would be under ~15 amps startup. A boiler furnace uses very little electricity but is necessary at all times for furnace to run.

If it were me, I would go with a cheap end generator like a 2500 to 3000KW. You would be able to use it for more things and be more of a friendly unit to use in different applications than a battery. Just my 2¢.

 

[OldShooter]

How about just running the generator in the day, when you can see it and protect it and then lock it up at night in the garage. ...

There is a chain and a padlock sitting on top of my generator. When I wheel it out I chain it to a fence post. My gamble is that the casual generator thief is not carrying bolt cutters. So far, so good.

 

[street]

I always find it interesting when stealing is part of our decision making. I don't believe I ever have had one thing stolen from me. I have many things of value at my ranch where people could steal and never had an issue. My home in town would be no problem letting a portable generator set out year around and not locked down. I'm sure some of it happens but we don't worry about things like that here.