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Floor heating system questions

Iggy05 Member Posts: 2
I purchased a house a little over a year ago and it has an in floor heating system in the basement ran off a gas water heater.  I actually have not turned this on yet.  More to come on why.  The house does have forced air throughout so this is more of a supplement system to bring up the heat in the basement to a more comfortable temp so I can live without it if needed.

It isn't exactly a closed loop system.  From the house water it uses what I can describe is a one way check valve that I assume fills up the heating system if it was ever to go low.  During our first summer in the house the bottom of this valve started leaking.  I am assuming this is basically works as a blow off incase the water pressure is too high.  So I shut of the water line before this valve.  It kept leaking for awhile into a bucket however the water was all slimmy to the touch so that was concerning if this is an issue.  Also the house is 20 years old and the gas water heater on it shows it's age and with the pile of rust in the bottem it is time to be replaced.

With all that said I have been looking at replacing the water heater.  As far as the check valve should I just remove it and turn it to a closed loop and fill it up with something different?  I am also assuming I will need to flush out the system somehow.  Sizing a water heater for this is confusing as well but I may just put something in that matches the current heater.  Any help is appreciated.  Thanks.


  • GroundUp
    GroundUp Member Posts: 1,649
    It's tough to say without a picture, but what you're most likely seeing is called a PRV (pressure reducing valve) which is indeed there to fill the heating system in the event it falls below X pressure. If it's not connected directly to the domestic water system at domestic pressure with no valving, it's still a closed loop system. Water heaters are not designed for space heating, so the correct thing to do would be to replace it with a boiler. Being low-temp radiant, a small condensing boiler would really shine in that application. The actual heat load is likely pretty low, being only supplemental in a basement. The auto-feed/PRV does not need to be there IMO, its only purpose is to mask leaks until it's too late. I never install them because if my system starts to leak, I want to know about it.

    With that said, sure you can just replace the water heater with a like unit if you want. Is it ideal? Not at all. But it will heat the space for awhile until it doesn't.
  • Can you post a picture of the "one way check valve"? Also, how many square feet in your heated basement?
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Jon_blaney
    Jon_blaney Member Posts: 313
    Not everyone agrees, but a high output water heater can be successfully used to provide heat to your home and provide the DHW at the same time. I have been doing so in the NE for twenty years with the same equipment. It is a 32 gallon, oil fired heater. You have gas, that will work. You can run low water temps and not be concerned with return water temperatures. These are simple systems. I use a Bock unit. I think water quality needs to be evaluated. Water quality has a lot to do with water heater and boiler longevity. A water heater can be the right choice.
  • EternalNoob
    EternalNoob Member Posts: 42
    I'm with Jon. The "rules of thumb" don't always apply on smaller scale. I've seen tanked water heaters used for radiant on small simple projects quite successfully. Complexity and sophistication should scale with job size. A 300 square foot ADU in California has 2% of the heating load compared to a 3000 square foot house in Vermont. Having said that i don't know enough about your system, but i would be wary to cast judgement that the system "wasn't built right" before doing a load calc. Most tanked WH's just don't spit out that many btus is the issue with using them in radiant for most jobs. The person who installed it probably pontificated on this question and decided using the WH wasn't a terrible idea.

    A decent mixing valve could be purchased for less than 100 bucks and isn't that hard to install. It would allow you to keep the tank at a higher temp (140, 150 df) and mix down to 110 df for the concrete, keeping more stored HW on hand, and expanding the capacity of the system if you think it's undersized. $100 mixing valve is a lot less than a new $2000 condensing boiler.

    The check valve you're talking about is a back-flow preventer which is like a double-duty check-valve with a drain at the bottom and is typical of closed loop radiant systems. Some water coming out the drain is not cause for alarm. Constant drip likely means it needs to be replaced but do some googling first. Agree the BFP and PRV aren't necessary but it makes refilling the system and flushing the air out easy which you may have to do a couple times if you are tinkering with it.
  • Iggy05
    Iggy05 Member Posts: 2
    edited January 2022
    Thanks. I see I should of had more information. The entire basement is a 1500 square feet or a 50x30. I am in Northern Wisconsin so it does get on the cold side here. I am not 100 percent sure if this system goes through the entire basement though as only a little over half is finished and the rest is storage. I kind of think it would have been but who knows. There are only two supply runs to it and at least looking at a lot of other examples of systems this seems very well on the low side. But it is using 5/8" pex. For a 1500 square foot basement maybe this is ideal. @EternalNoob it is in fact a backflow preventer as I didn't realize there was a label on the top side. In the pictures it is obvious now.

    I am generally very handyman capable on just about everything and I tend to over think the process. But I learn a lot in the process. So I tend to take a step back and think how this can be as efficient as can be and research on it as much as possible.

    Here are some pictures on what is there now if that helps with anything. I have looked around enough on the internet to figure out what everything does. This may or may not be a problem but the pumps label only shows it is good up to 110F. To me that sounds kind of on the low side right? Thanks for any help.

    This is what was leaking out.

  • I would get the system up and running and then find someone with an infrared camera who can show you where the loops are. That will tell you the area that's being heated and from that, what heat source is required, whether it be a boiler or water heater.

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab