Running Boiler During Power Outage

[Selk Perkner]

I have an older Weil Mclain gas steam boiler for the radiators in my house. If the electricity goes out, it won't run -- I believe it needs electricity to operate the gas valve, and the thermostat is also wired into a circuit.

Should electricity go out to the house during the winter, I could certainly get by for a few days with flashlights and coolers as long as there is heat. I have instructions for running the boiler manually, and could connect a battery operated thermostat, but would prefer to run it on a backup electrical connection if possible so I don't have to babysit it in the dark.

There is a single electical conduit running into the boiler which is connected to a box with an on-off switch above the boiler, as well as a line running from the thermostat.

The thermostat is obviously a straightforward job, but is it a straightforward job to switch the power at the on-off switch from the regular house current to a backup source? How much capacity will this backup need -- does it pretty much need to be a gas generator, or can I get by with a battery backup of some sort?

Is this just a quick project in the event of a major winter outage (assuming I buy the parts ahead of time) or should I get the guy who does the annual inspection do the work? I've done plenty of basic wiring like running cable for new outlets and lights and switches, so I'm not intimidated by basic stuff, but also know better than to mess with stuff beyond my pay grade.

[RBM]

First, the thermostat doesn't use a separate power supply, it gets whatever electricity it needs, through the boiler power supply. The type of system you have probably requires very little current, but not knowing the actual components involved, I couldn't tell if you could back it up with a low voltage power source. The easiest way would be to Install a switch in the 120 volt circuit that feeds the boiler, in conjunction with a male plug wired to the switch. With the switch in one position, the boiler would get it's power from the utility company circuit. With the switch in the other position, the boiler would get it's power from an alternate source that would be connected to the male plug. You could use a very small generator, like 1000 watts, or even use a battery backup pack, that delivers 120 volts AC.

[Malcom "Mal" Reynolds]

you'd need to provide more info, ie model number and all those pesky rating numbers, but as a guess you could do it with a battery, inverter and cutout switch.

if you were going to use a generator to provide the electricity, it would be easier to capture the waste heat instead of using your boiler

[Ed Pawlowski]

That would work. Can we also assume you have city water that is not interrupted to feed the boiler?

[gfretwell]

What is the draw? If this is fractions of an amp, a garden variety UPS should run you for quite a while.

[DanG]

RBM, so glad to see that you still haunt this NG. I've always trusted your electrical answers a bit better than some others.

[Mikepier]

As far as I know, the steam boilers only require 24 VAC for the gas valve to open. You should have a transformer inside the cavity of the boiler. If you could somehow get a 24 VAC transformer that you can run off lets say a UPS, or a car inverter, you should be good to go.

[George]

Good idea, most gas utilities won't even allow a manual bypass gas valve for obvious reasons since it bypasses all safety devices.

If it is just an old natural draft boiler without inducers or other electrical loads a UPS would work. If you wanted an elegant solution there are UPSs that can be hard wired. In that case you wouldn't have to do anything to switch over since the UPS would do it for you.

[trader4]

I'd start by measuring how much current the boiler actually draws. Then knowing that and how long you want to be able to keep it running you can determine if a UPS will fit your needs or if you need a generator. The advantage to a generator would be that it can last as long as you keep it fueled.

For about $400 you can get a 3 or 4KW generator. They also have kits available for about $250 that will convert it to run off of natural gas. That eliminates the need for gas and gives you an unlimited supply as long as the gas doesn't quit too.

If you go the generator route, I would look into a solution from Interlockit. They have kits where you can use a circuit breaker and their slide lock on many existing panels. That together with an inlet device would allow you to use an extension cord to connect the generator when necessary and power ANY loads in the house. You just have to manage the loads so that you don't exceed the generator capacity. That would allow you to run refrigerators, lights, etc of your choice in addition to the boiler. It's a simple modification and IMO a lot better than figuring out how to rewire just the boiler.

[George]

If his description is accurate his boiler has a typical standing pilot gas valve like this one which is the only thing that consumes power on the type of boiler he described (no inducer, no electronic ignition etc):

That is a 3/4" valve, his is likely a smaller 1/2" unless he has a huge house or high heat loss.

It says the anticipator should be set to 0.7A so that gives 16.8 va. Assume 50% efficiency and the load is 33.6 va.

A ~ $200 class UPS could easily hold that load up for two days with no need for storing fuel etc. Plus unless it is at outside design temp the duty cycle will be less so the only consumption will be losses in the transformer when the gas valve is closed.

[willshak]

Selk Perkner wrote the following:

Everyone in my neighborhood (a 3 mile long dead end street) has a portable gasoline generator that runs the whole house, including the well pumps. We don't have any utilities or services that don't come over pole mounted wires (electricity, phone, cable TV, internet) except for satellite TV, fuel oil, and propane. I think that our part of the electric grid is connected to the main grid by an extension cord running over the ground that somehow gets unplugged by a cow tripping over the extension cord. :-)

[Tom Horne]

"manual bypass gas valve .snip. since it bypasses all safety devices."

That is simply untrue. The manual bypass does bypass the thermostatically controlled solenoid gas valve but it does not bypass the pilot safety shut off system, over temperature cutoff, or the pressure limit safety. And nothing bypasses the pressure relief valve! He already said that he had the instructions for running the boiler manually. When such instructions are provided the safeties are all mechanical because electrically actuated safeties fail safe and prevent operation when the electricity is absent.

[George]

Okay, it bypasses essential safety controls.

not really much help if someone opens the bypass and lets the burners operate. The pilot already did its job at that point.

the gas valve is now turned on manually. No over temp cutoff is in play.

There is no pressure limit safety when the gas valve is manually bypassed.

The typical failure mode is that the water gets boiled off and the boiler turns red and sets the house on fire. BIL has his doctorate in engineering and owns an engineering firm. They do an extensive amount of accident investigation work and that info (and pictures) came straight from him.

He already said that he had the instructions for running the

Then why do you think the gas utilities in our area (one is a national outfit) will not allow a manual bypass to be installed?

[Tom Horne]

If you can competently install switches and receptacles then you can install this connection. Most boilers are not listed for cord and plug connection because they are "appliances fastened in place." [That is listing laboratory language that is used in an somewhat different way than similar language in the National Electric Code.] That rules out replacing the switch with a cord and receptacle which would be the simplest approach.

What you do instead is that you install a double pole, double throw, center off switch in place of the switch that is there now. Next to that switch you install a box with a flanged inlet type male plug.

It looks like the one in this picture

Cut and paste everything between the Less Than < and Greater Than >

signs into your browsers navigation field.

The grounded current carrying conductor (neutral) and the energized conductor of the plug attach to the terminals at one end of the switch. The existing grounded current carrying conductor (neutral) and the energized conductor of the dedicated branch circuit that supplies the boiler go on the other end of the switch. The grounded current carrying conductor (neutral) and the energized conductor of the boilers wiring go to the middle terminals of that same switch. You will need a continuity tester of some sort to test how the terminals on the switch are laid out so that you do not reverse the circuit polarity through the switch contacts. It is important, in some cases, that the grounded current carrying conductor (neutral) and the energized conductor of the circuit remain in the same polarity no matter which source is supplying the boiler wiring.

When a power failure occurs you throw the switch to the center off position, connect the cord from your alternate power source to the male blades of the flanged inlet, turn on that power source, and throw the switch to the other end from the normal power position to connect the flanged inlet to the boiler's wiring.

As George has already pointed out if you use a hard wired UPS or a a battery charging automatic inverter then it will do all of the switching for you.

-- Tom Horne

[Nikola Tesla]

The electric code dictates that you must use a device like the Reliance Controls TF151W. Reasonably priced and certainly easy enough to install.

[RBM]

That is pretty much exactly what Tom just described. I have to admit, the Reliance unit will be cheaper

[Vic Smith]

Time for my reminder in case the OP didn't think about this. Think about how many times you might have an outage in the winter. Think about if there's old folks who need good heat to prevent hypothermia. And about freezing pipes, and what you need for heat on a "temporary" basis.

Consider the final cost and maintenance of all this - generator, UPS or otherwise to power your furnace. Switching, possible electrician cost, possible permits. Keeping gasoline or diesel around if you go that way. Starting her up on a regular basis to make sure she runs when needed. But you won't be sure until you need it.

Then know that you can hook up a small 30k btu or better natural gas space heater on the floor or wall next to the furnace for maybe 200 bucks. No electric needed. Heat moves up from the basement. Depending on your kitchen range, you can get another 20-45k btu there.

Not saying a generator doesn't have plenty of other uses. But just for temporary furnace heat to prevent people and pipes from freezing, there's better ways.

--Vic

[dgk]

I hired an electrician to put in a switch that does exactly that. If need be, I can plug the boiler into the generator, flip the switch, and it will run. I could have done it myself probably but there were an awful lot of old wires around and I didn't want to mess it up.

However, since I bought the generator, the power does not go out. That's after several major storms and a hurricane that knocked out power to Long Island for quite a few days. Coincidence? Most likely yes.

[RBM]

Murphy's law, go with it!!

[Ralph Mowery]

I have had a 5 kw gasoline generator for about the last 12 years. We have had 4 power outages that lasted more than an hour. Generator would not start either time. Each time I had to clean out the sediment in the carborator bowl. I have started running it about 15 minuits each week or two. Also putting the Stabil in the gas. It will start with 2 or 3 pulls of the cord. Almost waiting on the next power outage to see if it will start this time.