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Thread: Radiant Heat

  1. #1

    Default Radiant Heat

    I have been trying to get an answer to some questions I have about my heating system. I have a four year old 1800 sq. ft. ranch (ENERGY STAR)home in Manitowoc, WI. Some of the reasons I'm not sure things were installed right:
    I have an OA sensor that was installed on the south side of the house where the sun was on it all day. I had it moved to the north side.
    There are two pex tubes in each joist space stapled to the sub floor, with no plates. There is 2 inch styrofoam (R-8) screwed to
    the bottom of the joists with 3 inch drywall screws and fender washersfor easy removal in case of problems.
    There is no difference for carpet, tile or laminate floors.
    The sun room (almost all glass would not come up to set temperature so the contractor came back and added some plates around the perimeter and had me install R-19 insulation under the tubes and over the styrofoam.
    I saw one of your programs where you put radiant heat under the floor with plates and ran 100 degree water through the system.
    I am running 175 degree water when the temp outside is around 40 degrees and about 200 degrees when it is around zero.
    Is there something I can do to improve the system efficiency?
    Would plates help?
    Would more insulation help?
    Is it necessary to run those temperatures?
    Thanks,
    Jack

  2. #2
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,622

    Default Re: Radiant Heat

    First let me state I'm not a heating guy. The plates act as heat sinks transferring the heat from the PEX to a larger area of contact with the floor. I can't help but think that would prove more efficient.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  3. #3
    Join Date
    Aug 2007
    Posts
    443

    Default Re: Radiant Heat

    Jack,

    Most of the questions you ask would be difficult to answer unless a heating contractor with expertise in staple-up radiant went into the house & took a look at the system.

    From the comments in your post, this system sounds like it was poorly designed to begin with.

    There's no way a radiant system should be operating at those temperatures---aluminum plates to prop the pex against the sub-floor to provide some heat mass & direct the heat up to the living space are always essential.

    This could end up being a legal problem where you would have a claim against the builder & installer of the radiant system.

    I've included a number of links below that cover radiant issues & the importance of a radiant design program run by computer that can calculate a lot of the questions as to whether a staple-up sub-floor system will issue enough heat to keep the building warm in winter---there are always things that can be done to bring the system up to snuff by adding more mass (bulk) surrounding the PEX tubing, increasing the gpm water flow, adding more loops, adding baseboard or convectors, blowing in additional insulation if necessary---but this will cost you additional money when you're legally entitled to a system that works to begin with.

    The "house needs" site has good basic info on hydronic radiant staple-up---the "all experts" site mentions Joist Trak by Wirsbo & Onix add-ons by Watts, as possible solutions.

    In basic terms, heat is measured in btu's/hour---a certain number of btu's/hr are oozing out of your house on a cold day, depending on type of construction, location, amt. of insulation, amt. of glass windows & many other factors.

    A very rough estimate of this number would be to take the total sq.footage of the house & multiply by a heat factor between 30 and 60 (30 = very tight house, lots of insulation, limited glass, mild climate; 60 = drafty house, bad windows, little insulation, cold climate).

    Thus 1800 sq.ft. X 40 = 72,000 btu/hr bleeding out of your house---this is just a rough estimate, you would have to do the free Slant/Fin program to be accurate.

    In a colder area 1800 sq.ft. X 50 = 90,000 btu/hr, or more may be the heat loss.

    This could be equally done room-by-room---take the square footage of a room, say 15 X 10 = 150 sq.ft. X 40 = 6000 btu/hr to heat this room (approximate)---the question is, how many btu/hr of heat is your floor producing to make up this heat loss??

    This heat loss bleeding out of the house on a cold day has to be made up by the heating system---especially the DISTRIBUTION part of the heating system---the piping/radiators/convectors, etc.--the other component is the boiler, which must have the 72k or 90k btu/hr heat output (or whatever it is) to make up the heat lost thru the walls & windows.

    The free Slant/Fin site below will give you an accurate number of the actual heat loss your building is experiencing---this can be done on a room-by-room basis, or for the entire house.

    The Slant/Fin program will also tell you if the heat being produced by the amount of PEX stapled in the floors is sufficient to offset this heat loss.

    Just from your post, something is drastically wrong, most staple-up systems are designed to produce 15-20 btu/sq.ft of heat which would only equal 27k btu/hr for the entire house or tops 30 btu/sq.ft. which would equal 54k btu/hr.

    If your entire heat loss is 72k btu/hr for the house you have a shortfall, which is trying to be made up by raising the water temp to the max & that could stress out the PEX--it tends to soften & bend at those temps, & could fail.

    There are many other issues a radiant heating contractor would look at---are the installed loops too long---none should be over 280'---is the flow rate thru the loops at least 3 gallons per minute--problems in either one of these areas could mean the water in the loops is getting cold before it returns to the boiler.

    Are the supply & return manifolds near the boiler operating properly, along with the circulators or zone valves.

    Were the floor loops designed with the heat losses in mind that you're experiencing in the Sun Room---sun will radiate heat in thru the day, but the loss will be considerable at nite.

    Thick carpeting is a no-no & the staple-up under-floor method can be problematic in cold climates because it doesn't have the MASS of a concrete slab or gypcrete slab to absorb & hold the heat from the hot water in the PEX---but some modifications can always be done to get more btu's out of each sq.ft. & make sure the rest of the system is operating correctly.

    Consult the Yellow Pages under "Heating Contractors" & find someone experienced in radiant to get an objective opinion of what you need for your system---another option would be a building inspector who would have knowledge of radiant heat--in either case get someone who can do a computer radiant design so they can check to see if sufficient PEX was installed---or if supplemental baseboard or other convectors should have been included.

    http://en.allexperts.com/q/Radiant-F...diant-heat.htm
    http://slantfin.com/heat-loss-software.html
    http://hearth.com/calc/roomcalc.html
    http://media.wiley.com/product_data/...0764542087.pdf
    http://media.wiley.com/product_data/...64542087-1.pdf
    http://www.houseneeds.com/shop/atop/...atingindex.asp
    Last edited by JacktheShack; 07-15-2008 at 09:19 PM.

  4. #4
    Join Date
    Aug 2007
    Location
    The Great White North
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    4,045

    Default Re: Radiant Heat

    There is 2 inch styrofoam (R-8) screwed to
    the bottom of the joists with 3 inch drywall screws and fender washers

    and had me install R-19 insulation under the tubes and over the styrofoam.
    This seems to be a signal someone was cutting corners or doesn't know what they're doing.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  5. #5
    Join Date
    Feb 2008
    Posts
    550

    Default Re: Radiant Heat

    Shack nailed it!

    I agree with McDaniel and Canuk that aluminum plates are needed, as well as a heat loss calc.

    I take exception to jkirk's claim that "infloor radiant isn't designed as a way to heat the house, only for sock feet"

    ***! This flies in the face of millions of successful staple-up jobs over the years in the U.S., Canada, Europe, and parts of Upper Silesia.

    Bill, Monica, Hillary, & Socks the Cat might have something to say on how hot it can get on the floor.

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