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Community and Q&A

Flow control valves for radiant floor heating

olsonphoto | Posted in Mechanicals on

I have high efficiency house in central Vermont. It has radiant tubing in the floor for heat. I am trying to get the on demand hot water heater, a Takagi, and the circulator pumps to run as little as possible. Electricity is the biggest obstacle. The house is off grid with PV and batteries. Both are a little on the small side. The house has 6 zones with flow valves on each. No zone is over 400 feet. Tubing is 1/2 inch PEX. Current Delta T when three or more zones are open is 10 degrees. I currently have all flow valves wide open. I wondering if I should slow them down to allow the hot water to spend more time radiating heat into the floors? I could also raise the temp of the water. Any ideas would be most appreciated. Thanks

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  1. user-2890856 | | #1

    Jon ,

    Visit . Ask your question in the radiant heating section . You will get the best advice there from heating professionals . Every year we help scores of people fix bad installs and answer questions that help them avoid issues .

  2. GBA Editor
    Martin Holladay | | #2

    I also live in Vermont, and my house is also off-grid. I have consulted with many people in your situation.

    I advise you not to invest any more money in your hydronic heating system. If the heating system of an off-grid house requires electricity to run, the homeowners usually struggle to keep it going for one or two winters, and then abandon the system.

    In all cases, homeowners in your situation end up installing one of two systems (often both): a simple wood stove without any fans, or propane-fired space heaters with through-the-wall venting.

    When you buy your propane space heaters, make sure that you choose models that don't require any electricity. Empire heaters are widely available.

    At this time of year, we go for weeks at a time with no sun. It makes no sense to use your gasoline-powered generator to make electricity to keep your hydronic heating system going. You should abandon your hydronic heating system.

  3. wjrobinson | | #3

    Martin has the experience to say what to do. All I would add is that if you keep operating your system, show us some pics, change to ECMs like the Bumble Bee circulator. I automatically takes care of what you are asking about. And Richard too has pointed you to a good heating site.

  4. olsonphoto | | #4

    ADDITIONAL INFO: The radiant floor heating system is primarily used to hold the house at 50. The house is a second home. We occupied I have a Morso sealed combustion wood stove that does the bulk of heating work. The 2200 sq foot house has a total heat load of 15,000 BTU. I thought about heating with two 60 watt light bulbs but what fun is that!? I have been thinking about switching to ECM. The battery bank is 24 volt DC so I could skip the inverter for that part of the system. Inverter eats 1 amp continuously . I can run inverter on search mode because rest of heating system needs constant source of electricity. Current load when both pumps are running is 1.8 amps. I suspect the ECM pumps are much more efficient. Thanks for continued answers.

  5. GBA Editor
    Martin Holladay | | #5

    If your house has a good thermal envelope, one or two space heaters (the type I described that don't require any electricity) is all you will need to keep the temperature above 50 degrees.

    If it's a second home, and is sometimes unoccupied, it's particularly foolish to choose a heating system that requires electricity. If you are not there to check the condition of your batteries daily, you don't know what's going on. Having a gasoline-powered generator or propane-powered generator come on periodically to keep your batteries charged in order to make sure you have heat is a very wasteful way to try to heat your home.

    It is far better to burn the propane directly to make heat, and to let the batteries rest.

  6. olsonphoto | | #6


    All good thoughts. Thanks. The generator thing doesn't happen more then once or twice a season for unoccupied heating. I have systems in place to monitor power and temp in house. The house has a fantastic thermal envelope and it doesn't seem to drop much even with eat off for days waiting for the sun, always waiting for the sun. Last year the total amount of propane used for DHW and space heat was 145 gallons total, for the whole year. Like all of us off grid folk, I'm just trying to geek out an already pretty greeked out system. The house is built slab on grade with under slab insulation of R20, walls of R40 and ceilings of R70 and 80. It is extremely air tight and as a Venmar heat recovery ventilation system that only runs when occupied. I've always been curious just how cold the house would get with no thermal inputs other then the sun through the many south facing triple pane windows. I'm not willing to experiment with burst pipes. Does Taco or another manufacturer make a Stainless Steel version of the bumble bee ECM pumps? I would need that for the DHW side of the heat exchanger.

  7. wjrobinson | | #7

    Jon, there a many circulators for potable water, some with delta T, some with timers, some for radiant.

    One site to browse and call for help.

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