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best flooring for hydronic radiant floor heat

Tracy Schmitt
March 19, 2019
We are building a home in Montana with radiant floor heat throghout the house. Are tile or hardwood or engineered wood best for conduction of the heat?

Comments (10)

  • SJ McCarthy

    Do you need ROOM heat or do you want "warm toes"? If you need to heat the entire house using in-floor radiant heat (I'm assuming you are going with hydronic?) then the best option is always concrete, tile or stone. They offer the least resistance which means the most amount of heat pours through them and into the house.

    If you want warm feet (because the rest of the house is being heated by a fully operational forced air or baseboard heat system) then you can have engineered hardwood as a lovely option.

    There are SOME engineered hardwood floors that allow it being used over hydronic in-floor radiant heat....but do NOT count on it being "OK" with every engineered product you look at. And if you go with hardwood, you do NOT want to used underlayment or soft underpad with the heating system. The underpad will block quite a bit of the heat, creating excess load on your heat system (in essence you are heating the pad under the floor while the room remains chilly).

    Carpet is an amazing product when used with in-floor radiant heat. Carpet breathes nicely. And the underpad is the thing that has to have the "hydronic heating" allowance which means you can choose the pad that is best suited for your situation.

    The other thing to be aware of with wood and in-floor radiant heat: low humidity. In-floor radiant heat is KNOWN to dry out wood flooring products. Because the wood is SOOOO close to the elements, the first thing that heats up (and dries out) is the wood. To combat this issue, you MUST add in humidity control in the home. That means you will need a system (separate from the heating system) that has the ability to add/subtract humidity throughout the year. In Montana the outdoor humidity is often very low to begin with. If you then decrease it even more with a dry heat, then the interior humidity levels can be extremely low. And wood does NOT like that.

    A wood floor requires humidity to "sit" around about 45% all year round. Please check your building specifications to find out HOW you are going to add that humidity to your home. And then find out if you have the ability to change the humidity levels with the touch of a button (humidistat). This usually involves a system with heating/cooling ducts so that moisture can be added to the air in an even way...

    For right now, I would assume you HAVE to go with tile/stone/concrete until you find out the HVAC humidity control system that is currently in place for your build.

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    Oak & Broad

    Tracy Schmitt , high quality American made Engineered wood flooring can be a good option if you make sure to have humidity controls in place as SJ McCarthy has already stated. Hydronic is really the only radiant heat system recommended for wood floors. An electric system can heat to quickly and damage the flooring. Look for a 5/8" thick product like in this diagram and make sure its recommended for radiant heat.

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  • Tracy Schmitt
    Thank you!! We will not have a humidifier. so that limits our options. also recommendation for best radiant floor heating system?
  • SJ McCarthy

    Your builder, who is well versed in heated slabs, will have speculated a few options for you. What are the plans for the slab? Is it fully insulated? Has it already been poured?

    The sourcing of in-floor radiant hydronic systems should be part of the original discussions with your builder. If they are unsure as to which system to use, then perhaps you will want to chat with someone who has a FULL understanding of the plus/minus aspect of in-floor radiant heat, humidity controls, air circulation (are you using a heat pump?) and air exchange requirements.

    I know that in cold parts of Canada (which are MUCH more difficult to deal with than Montana) the builders have to utilize SEVERAL forms of heating/cooling/air exchange products when working with whole-home in-floor radiant heat systems. The design aspects of these multi-system homes can become very complicated very, very very quickly. So much so that the build costs suddenly skyrocket simply because the "whole home" system was not properly designed at the beginning. The retrograde stuff (done AFTER most of the house is complete) becomes the really expensive things that can drive a budget to the moon.

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    The Cook's Kitchen

    Hydrionic is the only option for home heating with radiant. You pay a large premium for its use if you are in a location that also requires air conditioning. If you are in an area that does not use AC, the premium will be smaller. It is extremely comfortable, if you have the right expectations and knowledge of how the system works, and it’s limitations. I love mine!

    It does present design issues with the use of thermal mass and lag time. It is not an option that can be decided on at the last minute and have work well. It needs to be part of the original design brief so that it can be properly designed with. You just do some things differently when you have to deal with tubes of water in a concrete slab.

    Many people find that putting more money into the better insulated and air sealed envelope of the home combined with a forced air system to have better immediate payback. A better envelope also has continued long term payback regardless of HVAC type chosen.

  • Tracy Schmitt
    Thank you for all your comment!s!! This will be our whole house heating system. House will be built over a crawl space vrs slab. We will be using the staple up method.
  • Pinebaron

    Since you don't need AC, Hydronic is the way to go with stone or tiled floors but use warmboard or similar as sub floor for higher efficiencies. I would have saved a significant amount with Hydronic even for this large home however made provisions for AC and went the forced air route with additional electric radiant heating in select tiled areas.

  • SJ McCarthy

    It sounds like you will have a timber frame building rather than a cement slab foundation. You are welcome to have tile over the joist/subfloor BUT you must have the right DEFLECTION rating. Which means the joists (measured on centre) and the thickness of the subfloor (the amount/layers of plywood) need to meet a MINIMUM standard for tile. The subfloor/plywood CANNOT bend or have deflection...it kills tile inside of 6 months.

    That means one of two things:

    1. The joists are VERY close together (which means more joists which means more money); or

    2. The THICKNESS of the subfloor is SOOOO thick, it doesn't matter how far apart the joists are (which means less efficient hydronic heating which means more money to run a system that might struggle to begin with)

    Whew! How much design/construction/mathematics has your Architect/Engineer done to this point?

    One of the best floors for hydronic over wood subfloor = carpet.

  • Pinebaron

    It's all about foundations. Joists and their closeness and are only part of the foundation. The entire foundation design, support structure and subfloor will determine DEFLECTION rating. We have huge open spaces with tiles but our foundation was built for it with joist spans way below their rating and an over-engineered foundation to ensure a solid floor feel; an expensive option but ....

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