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Emergency question about gas hot water furnace

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by danham, Feb 10, 2013.

  1. danham

    danham Member

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    As you may know, Cape Cod got hammered by a big storm and a house I own has been without power for two-plus days. It has a gas-fired forced hot water furnace.

    I have shut the water off to the entire house and drained what I could of the domestic plumbing. The furnace pipes contain antifreeze. It acts like a closed system, with zones, but the boiler is also plumbed to a supply line, presumably to fill or flush the system.

    My question is: with the water turned off for the whole house, is it safe to operate the furnace? It takes me about 30 minutes to drive over there and so if the power comes back on I want to know if I should hurry to go turn the water back on.

    In other words, will boiler pressure escape through that supply valve? My guess is there should be a check valve as I doubt it would be designed to allow antifreeze to back up into the domestic water supply, but I've never had to deal with this before.

    Many thanks,

    -dan

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  2. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    Moving this to the boiler room where the pros at this stuff reside.
  3. Fred61

    Fred61 Minister of Fire

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    If your system contains antifreeze and it has not become diluted over time, that would indicate to me that you are safe to run the boiler. Is there a backflow preventer on the supply and if so, have you ever seen any drops of water coming off it? I would ensure that the fresh water supply is shut off for now and go ahead and run it? While you're at it check the boiler pressure. It should read a minimum of 12 psi to a maximum of 18 or 20 psi.
  4. danham

    danham Member

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    Thanks, Bart, for moving the post, and thanks, Fred, for your reply.

    Fred: I was working in the dark with a weak flashlight, so not sure if there is a backflow preventer. There is a separate shutoff handle on the supply line but unfortunately I left that open, not really thinking about all this stuff until I was half way home.

    I will definitely go back over there if I detect power back on (have an aswering machine hooked to the phone line), but if it comes on in the middle of the night I'm unlikely to catch it until morning.

    -dan
  5. Clarkbug

    Clarkbug Minister of Fire

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    There *should* be a check valve or backflow preventer like Fred mentioned on that line, especially since you have antifreeze in the boiler lines. You dont want any of the glycol working its way back into the potable water system. If you dont have one, you want to put one in. Honest.

    In the greater sense of things, you should be OK to run the boiler without having the makeup line to it. I run my system with the makeup line valved off. I would say that if you are thinking about it, I would go over and turn off the valve to the makeup line. Be sure to check your boiler system pressure to make sure that nothing worked its way backwards.
  6. danham

    danham Member

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    Clarkbug:

    That makes sense and there has never been any evidence of antifreeze backflowing into the house plumbing. The antifreeze has been a PITA because it corrodes zone valves, but for once I'm glad it's in there.

    Appreciate the help.

    -dan
  7. Clarkbug

    Clarkbug Minister of Fire

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    Sure thing! Hope you guys survive everything OK, looks like it was a bear of a storm out your way.
  8. danham

    danham Member

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    Thanks. The irony is that at my home (not the rental property with the gas hot water heat), we lost power for about four 30-minute intervals the first night of the storm (gusts to 82 mph), but have had it on ever since, so our nice fireplace insert is really just doing auxiliary duty and keeping the utility bills down.

    -dan
  9. danham

    danham Member

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    UPDATE: The power is back on so I went over there to check on things. First, there is a clearly labeled backflow preventer. Second, with the house water system shut off, pressures and temps looked normal based on past experience. All radiators in all zones felt warm. I turned the water back on so that the system can do "makeup" if necessary.

    Thanks again for the excellent advice here.

    -dan
  10. maple1

    maple1 Minister of Fire

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    Keep an eye on your system pressures. Sometimes the pressure regulator on the frash water feed can let water in when it shouldn't (simple piece of dirt for example). Ever since that happened to me once a few years ago I leave my fresh feed valved off.
  11. Bob Rohr

    Bob Rohr Minister of Fire

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    A glycol filled system really should not have an auto-fill valve connected to it. The potential to dilute the glycol when air burps out, or to re-pressurize the system far out weighs any benefit. Look into a glycol fill system from Axiom or other suppliers, or build a fill tank with an expansion tank pressurized with glycol. Install a LWC low water cutoff switch tom prevent the boiler from firing if fluid leaks out. Some codes require LWC on all boiler installations, most mod con boilers have them as standard equipment.

    This tank holds about 3 gallons of glycol pumped into the tank to about 80 psi. The fill valve regulates the pressure to 12 psi or whatever your fill pressure is. If you have a fill valve in place you could disconnect it from the domestic water line and add the pressurized glycol tank to that connection.

    A Webstone Purge/ ball valve is another way to fill the tank, it has a garden hose side port to pump the glycol into the tank.

    Attached Files:

  12. maple1

    maple1 Minister of Fire

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    Yes, you're right - I overlooked the glycol part.

    We've got glycol in an oil fired outbuilding here. When it was installed, they rigged up an old water pump tied into the system, with the inlet to that in a bucket of glycol. If pressure got down, you switch on the pump for a few seconds. It's never been used in the 10? years since it's been installed.

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