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  1. #1
    Join Date
    Jan 2006
    Posts
    8

    Default in-floor radiant heat for garage/shop

    thinking of using in-floor hydronic heat for my new garage/shop. anyone have any info or experience to share. I've heard you can use a hot water heater which seems to be a lot less expensive than the boilers I've seen. But, is that enough for michigan winters?

  2. #2
    Join Date
    Apr 2011
    Location
    Wasilla, Alaska
    Posts
    631

    Default Re: in-floor radiant heat for garage/shop

    I don't know about the water heater thing. IT may be doable, but would be pretty inefficient, and would require some complex plumbing.

    As far as radiant in the garage is concerned though, I am of the opinion that it simply isn't worth it. My short list;

    1. If you already have a boiler in place, a hydronic unit is far more cost effective.
    2. You'll hear people argue that its more efficient because you don't lose all your heat when you open the garage door like you do with a unit heater because the slab holds the heat. This is simply unfounded. It takes a unit heater a few minutes to warm the garage back up even with a major drop in temperature. It takes the boiler a substantial amount of time to raise the same air temperature even a few degrees with in-floor heat tubes. Do the math, and it evens out.
    3. Its riskier. If you're heat ever went out, there's a higher chance of damaging something with the tubes buried in a cold slab.
    4. Anyone I know who has radiant heat in a garage has moisture issues. Instead of water from your vehicle (especially snow melt) draining, it evaporates, fogs up windows, possibly promotes mold growth etc.
    5. If you don't have a boiler, it will probably NEVER pay itself off if you have to install one.
    6. The water heater scenario wouldn't be much better than a small boiler and would pose its own problems.


    I think the only good reason for in-floor heat in the garage would be comfort. And for most garages, comfort...not so high on the list.

    A unit heater with a blower is the way to go.
    Michael

  3. #3
    Join Date
    Jan 2009
    Location
    Danbury area of western CT
    Posts
    4,441

    Default Re: in-floor radiant heat for garage/shop

    I don't necessarily agree with that assumption Alaska.
    I did a remodel/addition project that included a 2500 sf garage with workshop and second floor office/exercise/movie area. Upstairs was hydronic baseboard, shop and garage were hydronic in-floor radiant heat. I worked through a pretty rough winter in there as the fabrication shop on this job and the temps were quite comfortable. Doors were opened as frequently as one might expect for a 3 car garage and recovery time was fairly quick. Initially acclimating the slab took some time as it was a huge thermal mass, but once there the cycling was not bad at all.
    If the system is isolated, a mixture of glycol will eliminated any chance of freezing. There is pex specifically designed for slab installs that can expand without cracking the slab in case of freezing. RThat project is six years old and has not had any problems that I know of. I speak with the owners regularly and the issue has never come up.

    Phil
    It's better to try and fail, than fail to try.

  4. #4
    Join Date
    Feb 2008
    Location
    Northwest Indiana
    Posts
    5,576

    Default Re: in-floor radiant heat for garage/shop

    Most important thing about this is how you insulate the slab and stem walls. Water heaters work well. If there is a concern about freezing use an anti freeze. If you do use an anti freeze do not tie the system to the domestic water system.

    Tom
    http://chicagocraftsmen.org/2011/06/261.html

    Check with the AHJ, what we say doesn't matter.

  5. #5
    Join Date
    Mar 2007
    Location
    Vancouver Island BC Canada
    Posts
    887

    Default Re: in-floor radiant heat for garage/shop

    I used an ordinary gas hot water heater (38000btu input) to heat my whole house in Canada. Granted, it wasn't the coldest part of Canada but there aren't any real warm places east of the Pacific. Back then, I got the hot water tank for free but even now you can get a gas hot water heater for around $4-500.00. A small boiler will cost many times that amount and I guarantee you that a boiler hook up is far more complicated than any hot water tank because of the much higher working temps and pressures.
    It does take a long time to heat up a slab and if you are in really cold temps I would think of using a heat exchanger off your tank with maybe glycol running through your slab. Picking the BTU's and circ pump size (and especially the materials inside the pump) is another issue.

    roger

  6. #6
    Join Date
    Apr 2011
    Location
    Wasilla, Alaska
    Posts
    631

    Default Re: in-floor radiant heat for garage/shop

    Quote Originally Posted by philthegreek View Post
    I don't necessarily agree with that assumption Alaska.
    I did a remodel/addition project that included a 2500 sf garage with workshop and second floor office/exercise/movie area. Upstairs was hydronic baseboard, shop and garage were hydronic in-floor radiant heat. I worked through a pretty rough winter in there as the fabrication shop on this job and the temps were quite comfortable. Doors were opened as frequently as one might expect for a 3 car garage and recovery time was fairly quick. Initially acclimating the slab took some time as it was a huge thermal mass, but once there the cycling was not bad at all.
    If the system is isolated, a mixture of glycol will eliminated any chance of freezing. There is pex specifically designed for slab installs that can expand without cracking the slab in case of freezing. RThat project is six years old and has not had any problems that I know of. I speak with the owners regularly and the issue has never come up.

    Phil

    Phil,

    Which assumption do you disagree with? Everything you say above I can 100% agree with. The glycol is great and should minimize the risk, but won't completely guarantee it. And that only takes care of one of the problems on my short list. I wasn't saying recovery times and comfort were a problem in case thats how you read it. Actually the opposite. Comfort level is much higher with radiant heat. What I was saying was that the radiant isn't really any more efficient, costs more, and should really only be used if comfort is your #1 priority.
    Michael

  7. #7
    Join Date
    Dec 2005
    Location
    Michigan
    Posts
    7,593

    Default Re: in-floor radiant heat for garage/shop

    Quote Originally Posted by Alaskan Son View Post
    4. Anyone I know who has radiant heat in a garage has moisture issues. Instead of water from your vehicle (especially snow melt) draining, it evaporates, fogs up windows, possibly promotes mold growth etc.
    Most areas around here prohibit floor drains in a garage, so there isn't anywhere to drain the snowmelt. Also, the OP said Michigan and our winters are very dry. Never a problem with moisture in a garage.

  8. #8
    Join Date
    Jan 2006
    Posts
    8

    Default Re: in-floor radiant heat for garage/shop

    I appreciate the input. As far as moisture goes, as long as the temp of the garage, and it's contents,are warm added humidity isn't a problem. The problem of temp heat in the past has been introducing warm, moist air into a cold environment, causing condensation on all of my tools and everything else in the shop. The system I install will be independent of domestic hot water, glycol filled. The foundation will have 2" styrofoam vertically around all foundation walls and under the slab at least 4' in from all exterior walls. I've been looking at boilers online and they seem rather pricey.

  9. #9
    Join Date
    Feb 2008
    Location
    Northwest Indiana
    Posts
    5,576

    Default Re: in-floor radiant heat for garage/shop

    Put 4” of foam under the entire slab. Get the wall insulation below the frost line.

    If there is glycol in the system in cannot be tied into any domestic water, clod or hot. You fill the system by pumping in your premixed glycol.

    Use a water heater.

    Alaskan,

    Wouldn't the snow melt no matter what type of heat?

    Tom
    http://chicagocraftsmen.org/2011/06/261.html

    Check with the AHJ, what we say doesn't matter.

  10. #10
    Join Date
    Apr 2011
    Location
    Wasilla, Alaska
    Posts
    631

    Default Re: in-floor radiant heat for garage/shop

    Quote Originally Posted by tjbnwi View Post

    Alaskan,

    Wouldn't the snow melt no matter what type of heat?

    Tom
    Yes, it would melt, but a warm slab can cause it to evaporate before it has time to drain.
    Michael

  11. #11
    Join Date
    Jun 2005
    Location
    The People's Republic of Minnesota
    Posts
    1,190

    Default Re: in-floor radiant heat for garage/shop

    I have two buildings that I heat. The first is 1150SF. It has radiant in floor, with 4" of polystyrene beneath it. The walls have 6" of fiberglass and the ceiling is spray foamed. We had a top of line ultra efficient boiler installed for about $12K. It heats very nicely and has quick recovery. I spend $700 per heating season on natural gas.

    The other building I heat is 1540SF it 10" of blown in insulation in the walls and 30" in the ceiling. This building is heated with a high efficiency forced air unit. I had it installed for about $4K and it uses about $1300 in LP per heating season. If I could have justified the cost, and if building was going strong like it had been, I would have put overhead radiant heat in.

    Given the choice between a water heater of a hanging unit for a garage I probably use the hanging unit. Even a very efficient water heater isn't going to hold a candle to a furnace.
    there is ALWAYS a better way waiting to be discovered-
    yfc

  12. #12
    Join Date
    Oct 2007
    Location
    Southern California
    Posts
    2,184

    Default Re: in-floor radiant heat for garage/shop

    I installed Wirsbo hydronic using QuikTrac on a first floor, primarily to avoid ducts and soffits and have been very happy with the result. American Water Heater makes a line of water heaters that are designed to do domestic HW and hydronic. They have another set of pipes coming out the side for the hydronic. One of the part numbers is PG10-34-100-2NV. They are usually available on e-Bay, for reference. They are not particularly inexpensive but are 95% effiicent, high BTU, high recover, all stainless construction, and should last for a long time.

    The Taco "X-Pump Block" is a fully integrated controller with a heat exchanger, two pumps (one for each side) and a Setpoint controller with Outdoor Reset control and Delta T limiting control. Very easy to install and small too: http://www.taco-hvac.com/en/products...t_category=345

    In the above installation, the circulating water runs between 80 and 85 degrees typically to maintain a room temperature of about 72 degrees. The Outdoor Reset controller varies the differential based on outdoor temperature. A nice system.
    HERS Rater • BPI Building Analyst • BPI Envelope Professional
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  13. #13
    Join Date
    Jul 2008
    Location
    Suburbia (Washington, DC area)
    Posts
    1,938

    Default Re: in-floor radiant heat for garage/shop

    Better hot water heaters and boilers are fairly close in efficiency, but most hot water heaters create a lot less heat than most boilers. HWH around 30-40K BTU/H vs boilers at 80K and up.
    The key question is whether a HWH can meet your load requirements, which requires a calculation of the heat loss in the building.
    Your specific project will have a different set of options compared to someone else's project. If the loads are small enough you can use a hot water tank and save some initial cost, at the probable price of some efficiency that will cost over the longer term.

    There are some other subtleties involving how much heat the floor piping, pumps, exchangers, and other parts can move around in a given time period as well.
    Your best bet is finding someone who knows enough about radiant heat to keep you on track. A local contractor could be the answer, nice in the middle of winter when there's a problem, but there are also mail-order radiant companies on the internet, or you may be able to find a good salesperson at a local plumbing/heating supply house who can help figure it all out.

  14. #14
    Join Date
    Jul 2009
    Location
    Vermont
    Posts
    611

    Default Re: in-floor radiant heat for garage/shop

    We are in our second winter with our radiant slab shop floor. The shop area is 30x32 with 28 foot vaulted ceiling and lots of windows. It has been ridiculously efficient. The key is a tight envelope. We shot the rafter bays with closed cell foam. There is only one degree of difference in temp between the floor and the ceiling 28 feet above.

    Here is a thread on our shop project: http://forums.jlconline.com/forums/s...ight=barn+shop

    I'd be happy to post a mechanical room picture if you are interested.

  15. #15
    Join Date
    Dec 2004
    Location
    Central New Jersey
    Posts
    789

    Default Re: in-floor radiant heat for garage/shop

    Scott,
    Thanks for the link to your shop project. It looks great.
    Looks like you have a lot of land up there too.
    Thanks
    Rich

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