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Thread: radiant floor heating

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    DIY Member devans175's Avatar
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    Default radiant floor heating

    I'm considering installing radiant floor heating in my kitchen. I'd like to use PEX tubing. My existing heating system consists of a hot water boiler and cast iron baseboard radiators. The temperature range for the boiler is set between 160 (low) and 180 (high) degrees. Can I run the same temperature water through PEX tubing? I'm planning a kitchen remodel and the cast iron baseboards will be in the way of the new cabinetry.

    I wasn't sure if I should post this in the heating forum or the plumbing forum, so I flipped a coin.

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    DIY Senior Member CHH's Avatar
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    That's too hot so the radiant zone will need a mixing valve to keep the water in the radiant loop safe for the pex.

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    DIY Member devans175's Avatar
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    I was woried about that. This means that I have to introduce fresh water into the system every time the heat comes on. The problem with that is I'm on a well and the well pump will kick on in the middle of the night... waking my wife up... not a good option. Is there any other way or do I need to look for another option to heat my kitchen?

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    Licensed Grump GrumpyPlumber's Avatar
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    There are ways to create indirect zones for radiant.
    Look around online for manifold systems specifically designed for this.
    "The biggest regrets we have in life are the chances we never took."

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    DIY Senior Member CHH's Avatar
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    Quote Originally Posted by devans175
    I was woried about that. This means that I have to introduce fresh water into the system every time the heat comes on. The problem with that is I'm on a well and the well pump will kick on in the middle of the night... waking my wife up... not a good option. Is there any other way or do I need to look for another option to heat my kitchen?
    Grumpy is pointing you in the right direction. Either use the mixing valve to mix return water with water from the hot side of the boiler or use a heat exchanger in an indirect hook-up. The choice probably depends on the design of the current system.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    While the pex can handle the heat, your flooring materials and you, too won't want it that hot. More normal water inlet temp to the pex for radiant is in the 100-130 degree range, depending on the structure and the heat loss.

    Before I updated it, I had a boiler that ran between 180-200 degrees...the water that is in the return line is cool enough to temper the water sent into the loop; you don't want to introduce new water on a regular basis to a closed hot water system...too much fresh oxygen and other gasses to have to purge. the oxygen can be the death of a boiler.

    An indirect system can be used, but normally isn't needed. Radiant floor heating is probably the most comfortable way to heat an area - you'll like it. Depending on the area of the kitchen, you may want a manifold and more than one loop to keep it more even. It is best to start the loop around the outside wall so the warmest water is near the coldest area.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Jack of all trades frenchie's Avatar
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    It's not like the mixing valve on your water heater, it doesn't introduce fresh water; it just mixes the two loops with each other.
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    DIY Member devans175's Avatar
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    Thanks for the replys. You helped me confirm that I can still install the system I want, but it's just going to be a bit more involved. I was concerned about the fresh water/oxygen issue. I recently installed a spyrovent to help purge oxygen from my system.

    I think I'll try to do the basic part of the install myself, then hire a pro for the more complicated parts. I understand PEXSupply.com will design the system and put together a materials list for a small fee. Seems like the way to go.

    Thanks Again!

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    Licensed Grump GrumpyPlumber's Avatar
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    Brace yourself.
    The stock is expensive, the manifolds come with special flow valves and other intricate parts.
    Thats probably the biggest reason radiant isn't more popular.
    "The biggest regrets we have in life are the chances we never took."

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    DIY Senior Member seaneys's Avatar
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    Quote Originally Posted by GrumpyPlumber
    Brace yourself.
    The stock is expensive, the manifolds come with special flow valves and other intricate parts.
    Thats probably the biggest reason radiant isn't more popular.
    I think of it as legos for adults.

    Steve

  11. #11
    Like an engineer alternety's Avatar
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    Be aware that there are two types of PEX. One for domestic water system has no oxygen barrier. The one you need for heating has an oxygen barrier. It is important that you get the barrier type for the heating system.

    Beware of online heating designs. There are some places out there that will really rip you off for a crap system (no, I don't know their names). Never use a heating system that feeds you domestic hot water through the heating tubes. Some of the more notorious online vendors push that approach.

    Pay attention to how you mount and couple the tubes to the floor. Also what the manufacturer of the floor covering has to say about maximum temperatures.

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