Non Electric Gas Boiler

[CharlieK]

Years ago I had a house with a natural gas steam boiler controlled by a milliivolt thermostat. When the power went out my boiler kept running having no need for electricity. As a builder we have a few clients looking to have their heat not be electric grid dependent. Anything made today that's more modern and effocient than my old unit that might do the same using NG or propane?

[BobL43]

check with your local propane dealer and/or the public utilty that supplies natural gas. That's what I would do.

[Dana]

Old-school high-mass steam or gravity-feed convecting hydronic systems rarely exceed ~60% efficiency, but there's no inherent reason a properly sized lower mass steam boiler with millivolt controls couldn't hit 70-75%. I'm not sure that would meet minimum efficiency & valving safety standards for legal sale in the US though.

Convecting millivolt wall furnaces exist (probably operating in the ~75% efficiency range), eg:

http://www.empirecomfort.com/EMPIREC...llFurnaces.pdf

There are probably low-voltage DC versions that could run code-legal valves, but it still wouldn't meet code on minimum efficiency.

To get higher AFUE efficiency than 78% usually requires some sort of blower or pump to generate sufficient turbulence for more effective heat exchange.

http://www.empirecomfort.com/EMPIREC...fficientDV.pdf

[Tom Sawyer]

But Dana, he wants to know if he can get a new one and as far as I know the present energy standards won't allow anying with a standing pilot for heating.

[Dana]

For hydronic boilers 80% AFUE is achievable and legal with standing pilot ignition, but that requires pumps and some power to run the gas valves.

Min-legal spec on steam is 75% AFUE, (also achievable with standing pilot, without forced-draft burners), but codes don't allow the type of gas valving used on millivolt systems, so it's still grid-dependent on the internal controls, even if it uses next to zero electricity.

So bottom line, no, with the possible exception of off-grid cabins other situations where millivolt wall furnaces might be permitted, your options for zero grid-power heating systems are nil. Some DC-systems with designed for big RVs and the like might cut it if your heat loads are miniscule, but I don't have a handle on that market.

[hj]

The "nonelectric" boilers had to be either steam or gravity hot water, neither of which is very popular these days. A thermopile could operate a gas valve to turn the burner on and off, but that was all.

[Tom Sawyer]

Besides the advent of more complicated and safer control systems the main reason why you can't do what you want is because millivolt thrermostatically controlled gas valves had a nasty habit of failing in the full on position.

[BadgerBoilerMN]

There is little purpose in being "off the grid" if you have to depend on the propane truck.

Answer; wood-fired out door boiler with DC motor.

[tk03]

As everyone stated above the Milli-volt is no longer available in boilers. You can still buy 24 volt standing pilot boilers. Manufacturers can build them until Sept 1, 2012.

Badger good point about the LP truck.

[hj]

quote; There is little purpose in being "off the grid" if you have to depend on the propane truck.

That is why the propane tank has a gauge on it with the red zone being once it reaches 20%. You should NOT wait until it is empty to call for a refill. If your propane truck cannot get to you with a couple of week's notice, you are buying from the wrong company.