Gas heat thermostat if no power

Way too little information - what is needed:

Type of heat:

a) If there is no power, a furnace with a blower will not work, full stop. b) If it is an hydronic boiler with a circulator, it will not work, full st op. c) Anything with spark or hot surface ignition will not work. full stop. d) If it is a steam boiler with a standard vent hood, standing pilot, and a millivolt-style thermostat (which was common enough in 1965), it will work as always, as it does not depend on line-level power. e) If it is an old octopus furnace (obsolete in the 1930s, much less the 60 s) as above, it will work as always as it does not depend on line-level pow er. f) If it is a gravity hydronic system, millivolt stat and standing pilot, a s above, it will work as always, as above. g) No oil-fired system will work as it needs mains-power to run the gun and the ignitor. h) And, obviously, electric power will not work.

Even if you have installed a modern thermostat on a millivolt system - the batteries inside the stat should maintain function power-failure or not. We change ours with the spring time-change every year, even though it is for a mod-con hydronic boiler with three circulators. But if the batteries go d own, the stat goes down.

Peter Wieck Melrose Park, PA

That depends upon what type of heat, a fact that you left out.

Read Peter's post. it is extremely unlikely you have a system that will wo rk. A low pressure (

The gravity furnace[*] in my San Francisco house is much newer than the

1930s. From memory the nameplate is mid 1960s. I suspect -- this would fall under "happened long before I lived here" -- that the building had a gravity furnace installed when originally built (1906), or shortly thereafter, and in the 1960s someone decided to replace the furnace but didn't want to reduct, so just put in another gravity furnace.

I seriously dislike it, the lack of forced air means you can't have filters, and the lack of filters means it smells of decades of accumulated dust every time it is turned on. I think we ended up using it only one or two days in the calendar year of 2020. It works, although slowly, when we do turn it on, but mostly we find other ways to keep warm.

The ducts are all asbestos insulated, so tearing it out won't be fun, when the time comes. The thermostat is is one of the old mercury switch types, probably installed at about the same time. Mercury switches are fun.

Elijah

------ [*] "octopus furnace" is a slangy name for "gravity furnance"

Noted, but I wanted to drive the point home.

It appears that the asbestos is on the outside of the ducts, not the inside. At least the parts I can easily see all match that.

What? In my mind "1 gray = 100 rads". That doesn't jibe with 300 gallons.

We have used electric space heaters on maybe five days in the last three months, and have been averaging $160, just over half of that, per month. These have been some of the more expensive PG&E bills we've seen, too. The cost of inaction is much less than the cost of action.

The first big win for removal would be all of the usable space that can be reclaimed from the furnace and ducting. (Ducts in the walls are not counted here as "usable space". This thing occupies a good percentage of the garage / basement space.) The second big win would be "not worrying about the asbestos exposure risk" in the garage / basement.

Elijah

------ that bill includes electric car charging, too

38 radiators, average 1.8 gallons each = 68 gallons 0.652 gallons per foot of 4" pipe. 120 feet = 78.2 gallons 0.37 gallons per foot of 3" pipe. 120 feet = 44.4 gallons 0.135 gallons per foot of 1" pipe 400 feet = 54 gallons 0.0229 gallons per foot 3/4" pipe 500 feet = 11.5 gallons Boiler Content, 2 gallons = 2 gallons

Comes to 258 gallons of water in the visible piping, 8 pairs of risers and the boiler itself. It does not count the expansion tank, piping in the craw l-spaces, or the piping around the boiler and indirect water heater. Just t he original iron pipe. It is a 3-zone, 2-pipe system with 3 circulators. So , I think I am pretty safe using 300 gallons as a round number. Our boiler is a WM Ultra 230,000 BTU mod-con that replaced the 400,000 BTU steel oil-b urner that was in place when we bought the house in 2008. The math was easy .

Average 6 hours of operation per day for 120 days as the base-line. And bas ed on use-figures supplied by the realtor. Oil at $2.50 gallon (130,000 BTU per gallon). Natural gas at $0.77 per therm (100,000 BTU). Oil Boiler at 55% efficiency (typical of a 1960s steel boiler measuring 6 f eet cubic - really). Gas boiler at 95% efficiency (published specifications)

(6 x 400,000)/130,000 = gallons per day. 18.4 gallons per day.

120 x 18.4 = 2,215 gallons per season - this is a backwards calculation from the supplied use figures. 288,000,000 BTUs expended 158,400,000 BTUs delivered $5,537.50 expended on fuel.

For gas (NOTE: Work with the DELIVERED BTUs, not the hours of operation!):

158,400,000/0.95 = 166,736,842 BTUs to be expended. Comes to 1,668 therms Comes to $1,283.80 expended on fuel.

Comes to a seasonal savings of $4,254

As I did 60% of the work myself, using a registered master plumber and cont ractor to do the demolition and final inspections, the entire installation paid for itself in three (3) seasons. That includes the cost of replacing 1

7 radiators and three pairs of risers - the house sat empty for two years ( REO) and the system was left full.

I did enjoy the reference to the Simpsons - so the joke was not lost on me.

"The coldest winter I ever saw was the summer I spent in San Francisco."

- Mark Twain

Peter Wieck Melrose Park, PA

Can't say about your system. We have hydronic heat here (water-filled baseboard radiators, a circulating pump, zone valves and 24 V AC gas valve. The zone valves have a manual override catch that will lock them open. I guess that was provided in case there was hope of convection, but I doubt it would work on our system.

Some gas valves have a manual override to turn the gas on, but you'd need to be VERY careful to not overheat the heat exchanger without the line-powered fan or circulator.

What we did was disconnect the furnace from the hard-wired power and connect to a generator. It is apparently illegal to have a furnace fed from a plug, so we have to unwire and then rewire every power failure.

A gas-fired furnace doesn't draw very much electrical power.

Jon

We have a small 30A @ 240 VAC emergency generator. When it is in use, we ru n it to a 30A double-pole breaker in the panel, shutting off the main break er at the same time. That will cover the freezer, refrigerator, boiler a fe w lights and other miscellaneous items as needed, without having to wire or unwire anything. The feed from the generator is 6/3 SJO cord, and the unit itself is grounded to a properly installed 8' ground rod. The three times we have had to use it for more than a couple of hours, it has worked nicely . Usually, we run a single-ended extension cord to our neighbors for their refrigerator as well.

Peter Wieck Melrose Park, PA

Yes, we have a much smaller generator. We have only used it once for an extended outage. It was WONDERFUL to have it, though. We ran extension cords all through the house, and ran the refrigerator, freezer, cell phone chargers and the furnace.

Since the events where this has been needed are so rare, having to rewire the furnace is not a big deal. I'm more worried about the gas valve thermocouple going out in the middle of the night.

Jon

run it to a 30A double-pole breaker in the panel, shutting off the main bre aker at the same time. That will cover the freezer, refrigerator, boiler a few lights and other miscellaneous items as needed, without having to wire or unwire anything. The feed from the generator is 6/3 SJO cord, and the un it itself is grounded to a properly installed 8' ground rod. The three time s we have had to use it for more than a couple of hours, it has worked nice ly. Usually, we run a single-ended extension cord to our neighbors for thei r refrigerator as well.

I assume the 30A double-pole breaker is wired to be a transfer switch, else , bad things will happen when the power comes back on. In your configuration, wont you need to drop some load at the load center a s I assume all the devices in a 3-4 bedroom house would exceed the power ou tput of the generator? Just re-read the post...30A@240 VAC...probably not .

Unless the power line going to your house is the only line down, the small generators would most likely trip out their breakers due to trying to power up other houses on the line.

I have a small generator 3.5 kw and another 5 Kw and I cut off all my heavy current users such as the water heater and heatpump. I only use one generator at a time as the 3.5 generator is propane powered and I use it for short periods of time . If the power is out longer, I then put gas in the 5 kw one and use it. That way I do not have to worry about gas being left in the fuel system and gunning it up. The 5 Kw unit will power the water heater if it is almost the only load other than a few lights. That way I can heat the water and take a very quick shower if needed. It will also let me use the electric stove for more than one small burner.

".... Shutting off the main breaker...."

We are a gas-fired, nearly-all-LED house. The loads I will drop for such an event are the hot-tub, the mini-splits, and the TV & audio solid-state electronics. Otherwise, there is more than enough capacity for lighting, refrigeration and heating.

Peter Wieck Melrose Park, PA