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Drain unused hot water system?

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1915_foursquare
1915_foursquare Member, Email Confirmation Posts: 16
We have a two story balloon framed house from 1915, in western MA. There is a gas boiler and cast iron baseboard radiators, but we put in mini splits and don’t intend to use the boiler except in an emergency (long story).  Since the radiators are on external walls, most of the pipes to the second floor radiators pass through external walls, which have blown in cellulose.

Should we drain the radiator system to prevent freezing pipes, or is that not an issue as long as the house is heated?  What outside temperatures would pose a risk of freezing pipes?

Thanks!

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  • Jamie Hall
    Jamie Hall Member Posts: 23,655
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    Well... the problem is what nature of emergency do you expect? Will you be there? Will the house have been heated up to the onset of the emergency? Is domestic water to be laid on?

    The basic problem is that if you attempt to start up the system when the house has already dropped below freezing, the pipes will freeze before you get enough warmth to keep things from doing that. Thus, if you are not there or don't have an on-call maintenance person who is VERY responsible, you may have difficulty.

    If the anticipated emergency is such that you may need to start up any time, I would suggest that you fill the system with an antifreeze (glycol) mixture and leave it and run it that way -- and that you run it from time to time, whether needed or not.

    As to what temperature might pose a risk, that depends entirely on how long it takes for someone to get there and turn on the boiler and the pumps. If it's going to be a matter of a day or two, then anything much below say 25 is risky -- and really cold you may only have a matter of an hour or two.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Alan (California Radiant) ForbesEdTheHeaterMan
  • Steamhead
    Steamhead Member Posts: 17,008
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    Those mini-splits won't work well if it gets below freezing. Keep the boiler ready for when it gets cold. You are going to be living there over the winter, right?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • 1915_foursquare
    1915_foursquare Member, Email Confirmation Posts: 16
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    Thanks for that well thought out reply.

    The boiler would be for backup in case the mini split system is down; if that is for scheduled maintenance, that is one thing; unscheduled is another. Scheduled maintenance would likely be some time other than the heating season, though.  We do have a good HVAC company on call who have serviced the boiler and who installed the heat pump.  

    We also have a wood stove for heat, and plenty of wood, so as long as we are home - which we are, 51 weeks of the year or so - keeping the house above freezing should not be a problem.  

    Worst case is if we leave the state for a week in the winter and the heat pump dies, in which case the cat sitter would have to call the HVAC guys.  We don’t anticipate going anywhere this winter, but some years we do visit relatives for the holidays.

    I’d have to look into whether glycol would work in our system - Weil McLain 97+.
  • 1915_foursquare
    1915_foursquare Member, Email Confirmation Posts: 16
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    Steamhead, we will see.  We got the Mitsubishi hyper heat units and family and friends who have them have been happy in the winter. And there is the wood stove.
  • leonz
    leonz Member Posts: 1,186
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    As Jamie said you need to invest in some non toxic boiler antifreeze like the cryotek brand to protect the system if you are not going to use it at all.
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,917
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    In the case of a prolonged power outage, the boiler isn’t working either, so while it can serve as a backup of sorts, it won’t be perfect. The wood stove is the most reliable, if you’re around. 
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,840
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    Put an outdoor temperature control on the circulator pumps with a manual switch to activate it. If you leave during cold weather put the manual switch on and allow the outdoor control to activate the pumps at below 40 degrees. Below 40 degrees start the pumps if you are away.

    With the house warm from the mini splits the heat in the house circulating will keep the pipes from freezing. Small $$$$ for some protection. I would avoid glycol crates a lot of issues.

    You can also have a temp sensor on your phone to check the house temp if you are away giving you time to get someone over there.
    Alan (California Radiant) Forbes
  • Jamie Hall
    Jamie Hall Member Posts: 23,655
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    Antifreeze is a somewhat contentious issue, granted. I'd use it, unless I was quite sure that I could keep the house above freezing with the grid power off.

    Similarly the 'phone notification. Our modern communications systems are just wonderful -- when they work. With the power off, the wi-fi or cell phone transmitter in your house won't work.

    And one other note -- not to take anything away from @EBEBRATT-Ed 's comments... getting someone over there, Christmas Eve at oh dark hundred in a blizzard can't depend on someone you happen to know in the area. If you leave for a week, perhaps a neighour can be persuaded to be your watch dog. If you leave for longer, you need to have someone who is very reliable lined up and committed in advance to pay attention. Trust me -- the money is well worth it. My daughter and I just recently completed a tragic job where the designated person was not as diligent as he might have been, and a pipe froze... and the house -- a lovely mid 1800s house, fully restored, with beautiful things inside -- was a total loss, with all its contents.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • 1915_foursquare
    1915_foursquare Member, Email Confirmation Posts: 16
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    Thanks to all.

    Would I be mistaken in taking away from this that:
    1) if the mini splits are working, the pipes should not freeze.
    2) if power is out, and we are home, we will be using the wood stove anyway; I know from experience that at least in non extreme winter temperatures, the wood stove has kept the house warm enough that the pipes didn’t freeze, for a week at a time
    3) if we are away in the winter, have someone dependable who can check in the house and either get the HVAC company in, or fire up the wood stove enough to beat back the cold.  We have family (who often heat with wood) a couple of miles away.  If the roads are impassible when we are gone, and the heat pumps fail, then we are out of luck, of course.

    If we are away we could always turn the boiler on and set the target temperature to something low.  Electricity outages would still be a problem but it would provide some backup in case the heat pump fails for some other reason.
  • Jamie Hall
    Jamie Hall Member Posts: 23,655
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    I have to chuckle a bit over your item 3 there, @1915_foursquare . We take care of several houses and a church locally. And people wonder why we have four four wheel drive heavy duty pickup trucks with honest to gosh winter tires... and no, it's not for plowing -- that's contracted out.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,840
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    If the pipe is inside the outside wall there is no guarantee against freezing except glycol.

    If it was me I would make sure the boiler is in ok shape to run and run it occasionally to make sure. Set the boiler thermostat a little below the mini split temp and your going to be pretty good. Just have someone check the house and get a temp app on your phone.

    Nothing is 100% but if you do those things you have certainly cut down on the possibility of freezing.
    WMno57
  • WMno57
    WMno57 Member Posts: 1,408
    edited November 2023
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    1) if the mini splits are working, the pipes should not freeze.

    The pipes for the hydronic heating system in the exterior walls are going to be the first to freeze in cold weather. If that hydronic system is dormant and the water is just sitting there, it doesn't matter how you are heating the house, mini splits, burning wood, whatever. The first part of the house to drop below 32 will be the interior wall cavities of the exterior walls.
    Your pipes haven't froze for 108 years because the water in those pipes was warmed and circulated by the boiler.
    This is why good cold weather design does not place bathroom or kitchen plumbing on exterior walls. If that design principle was ignored then prepared people who live in those homes leave the bathroom and kitchen cabinet doors open on cold nights to let some of the house heat into the walls.
    If you drain it, it will rust and corrode and be worthless. If you fill it with glycol, that introduces other problems.
    So use it, or lose it. If I owned your house, I would keep the system full of water and run it once a week. I would also run it whenever the overnight low was below some temperature. I also might run the pump without the boiler on mild nights.
    If I was going away for a week, I would have two thermostats, one for the boiler set at 55, and one for the mini splits set at 60. I would shut off the water for the house, but not drain the pipes, both potable and hydronic heat.
    1915_foursquare
  • 1915_foursquare
    1915_foursquare Member, Email Confirmation Posts: 16
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    The HVAC company suggested that I close the gas valve to the boiler, set the thermostat high, and run the boiler.  That causes an ignition error message but makes the pumps circulate the water to keep it from freezing.  Can you see any downside to that solution?
  • Jamie Hall
    Jamie Hall Member Posts: 23,655
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    Yeah... if the air temperature is significantly below freezing, somewhere in the system there will be a pipe with lower flow. Which will start to freeze. Which will lower the flow more. Which will freeze more... and eventually freeze shut. Just because the water is moving doesn't mean it's moving everywhere, not does it mean it can't freeze onto the wall of a cold pipe.

    Hold the interior at 50 to 55 with the boiler. Or glycol the system. Or drain it completely. Take your pick.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England