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Radiant Heat in the Northwest


We are looking to a build a single family home in the Seattle/Puget Sound area in Washington State. We really want to use radiant heating, but have a few questions and want to get an honest opinion.

1. Will the floors actually be warm when you walk on them? I've heard that in a modern home with good insulation, a hydronic floor system doesn't run hot enough especially as winter temperatures are only in the 20's-30's. Will it still be more comfortable than forced air even if the floors don't get super warm?

2. The contractor just wants to install ductless minisplits. Would installing the minisplits as well as electric radiant heat in just bathrooms/kitchen be a good alternative option to full hydronic?

We are interested in radiant because of the higher level of comfort, no blowing air, and also in the winter I often get "chillblains" on my feet which means I have to keep them warm.




  • Gordy
    Gordy Member Posts: 9,514
    Warm floors

    At best floors will be neutral , like 75-77 range. Unless the home envelope is poor.

    Mini splits are quite efficient if you don't mind the look. And doing floor warming in sensitive areas is a good option. Depends on your utility rates.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Will the floors actually be warm when you walk on them?

    Do not count on it. I am in New Jersey, where the design temperature is 14F. However this year, it has gone down to much less: just under 3F twice, and just under 7F last night. When it does that, the floors do get warm. If it goes down to 0F outside, I put 128F water into the slab (you may not want to go that high if you have hardwood floors). At 14F (design temperature) I put 114F into the slab. The surface temperature is less than that, of course. Sometimes the floor is pretty cool, mostly it feels like it is room temperature, and now it feels warm. That is for a concrete slab at grade.

    I happen to like radiant heating, and if you have a slab at grade, it is nice to have it take the chill off the floor. But do not count on it being warm to the barefoot touch except on very cold days.
  • Zman
    Zman Member Posts: 7,328
    A good read

    You are wise to be considering this.

    This article provides some good insight.


    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • SWEI
    SWEI Member Posts: 7,356
  • Paul Pollets
    Paul Pollets Member Posts: 3,508
    More info

    If your considering radiant heating, the more you know, the easier it is to make an informed decision. RFH has a higher installation cost than forced air, but will heat your home with extreme comfort and low gas bills. Typically 50%-60% less than a forced air system in Seattle. The system also makes the DHW for a residence.

    You'll also have to ventilate the residence to the WA State energy code to provide .35 air changes per hour, but that's another story.

    Here's an important read:

  • jakethesnake
    jakethesnake Member Posts: 2

    Thanks for all the great info, going to check it out :)
  • Sal Santamaura
    Sal Santamaura Member Posts: 381
    Interesting post -- some additional research

    Paul, I found your statement

    "You'll also have to ventilate the residence to the WA State energy code to provide .35 air changes per hour, but that's another story."

    intriguing, so looked into it further.  I located and reviewed Chapter 51-11R-WAC, Residential Provisions.  References to air changes per hour mostly concerned tightening envelopes, specifying maximum allowable values of 4 or 5.  The only place I saw mention of whole house ventilation invoked Section M1507.3 of the International Residential Code, which addresses ventilation rates for kitchen and bathroom exhausts.

    Undoubtedly, I've missed or misread interrelated provisions in the WA State Energy Code, International Residential Code and other controlling documents which lead you to imply that a very tight new home in your state, using hydronic radiant heat, *must* have continuous mechanical ventilation which maintains a minimum of 0.35 air changes per hour.  Would you please point out those code sections?  Also, do they require such mechanical ventilation even if mandatory blower-door testing shows a natural ventilation rate just low enough to meet the 4/5 air changes per hour specification?  Do newly constructed homes with forced air heat "automatically" cause enough air exchange due to pressurizing the envelope that they're exempt from the 0.35 requirement?

    Thanks in advance for your follow up.
  • Paul Pollets
    Paul Pollets Member Posts: 3,508
    edited February 2014
    WA State energy code

    All new homes or any renovations of over 50% of structure must provide ventilation to exchange .35 ACH. (not 4 or 5). Forced air systems typically use an economizer package with a 6" damper installed on fresh air duct with timer to allow fresh air into the return plenum to satisfy the requirement.
  • mjcromp
    mjcromp Member Posts: 57

    1. With a air/floor thermostat you can keep your floors at a minimum (whatever seems comfortable for you) while maintaining a constant air temp.

    2. A ductless system is good for backup/air conditioning.

    As far as the comfort goes, you can't beat it!
    Too bad common sense isn't very common.
  • Sal Santamaura
    Sal Santamaura Member Posts: 381
    Thanks Paul.

    Are those forced air systems required to run fan-only for ventilation when no heat calls occur over an extended period, such as during shoulder seasons?
  • Paul Pollets
    Paul Pollets Member Posts: 3,508
    .35 ACH

    Yes, If you have the economizer package for fresh air on the furnace, it must be on 24/7. Those who can, use HRV's since there are less than 5 cooling days per year in Seattle. Eastern Washington is very hot in the summer, and A/C would be much more common.