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#75561 03/03/07 10:31 PM
Joined: Aug 2005
Posts: 265
Sixer Offline OP
I have a job that has a boiler system with multiple zones (in floor heating). The garage is also heated - separate zone. Customer is complaining the garage is too warm - the lowest setting the stat goes is 10C (50F). I've looked around and can't seem to find one that goes below 10C. Switching it off is not an option because of the risk of the lines in the concrete freezing. Any of you know of a low voltage stat that will go below 10C and that you can't completely turn off?


"Will it be cheaper if I drill the holes for you?"
#75562 03/03/07 11:04 PM
Joined: Dec 2004
Posts: 209
Try Then search keyword "low voltage thermostat. You will find several heat only that go 40 to 80 or 40 to 90.

#75563 03/04/07 12:47 AM
Joined: Jul 2004
Posts: 9,822
Likes: 20
You can trick a mercury thermostat by mounting it at an angle. I did this with one in my spa surround when I lived in the frozen north. I put it on one of those swivel hickeys and rotated it until the range got to my liking, then locked it down

Greg Fretwell
#75564 03/04/07 05:25 AM
Joined: Mar 2005
Posts: 1,803
I have underfloor heating from a boiler with water supplied at 40C. To protect the floor pipes from frost is absolutely vital [ when I'm on vacation for example ], but using heat from the boiler to do this poses several problems. These floors have huge thermal inertia, a 6" concrete pad for even a small single-car garage will weigh over 4 tons and take several hours to warm up. It will absorb and emit a lot of heat from 40C water before triggering any stat, even one which is fine tuned to 4 or 5 C, below this one risks ice formation before the boiler lag can supply the necessary warm water. If the garage is not well insulated and draft proofed, that adds up to a lot of money. Even if you manage to switch the zone-heat on at 5C air-temperature, your customer will still 'feel' the heat [and the dollars!] coming off the floor- we humans are quite sensitive to infra red radiation. A single-bay garage could cost 20c an hour to frostproof with boiler calls. It begs the question; why did they fit UFH to the garage floor in the first place, if the heating is only turned on the protect the pipes!!?

3 solutions;

#1 I eventually went for antifreeze plus a corrosion inhibitor. Use ONLY polypropylene glycol, [food grade], up to 30% depending on frost severity - it's about $10 a gallon. Do NOT use automotive ethyl-glycol, which can eat rubber seals and corrode some metals and cause valves to 'stick'. Ethyl-glycol is also very toxic. Imagine a leak contaminating the whole house, the kids and Muttley paddling about in it!

#2. Insulate the garage floor surface to reduce it's emission of heat, since virtually all the energy leaves the floor as IR. This could be done by laying cheap polypropylene carpet, or by laying a masonite or plywood floor layer, or possibly with paint. Aluminum or white gloss floor-paint has a much lower emissivity than concrete.

#3. Abandon and mothball the garage UFH zone at the manifold, then blow out the water with air or refill with antifreeze.


As a postscript, another refinement might be to fit a remote bulb type thermostat onto the floor water return line in the garage, in addition to the existing 50F air-stat. The air-stat initiates boiler call, but as soon as the garage return flow hits, say, 10C, the water-stat closes the garage zone valve and closes boiler call. You'd need to run a trial to decide on what return water temperature is acceptable, but I would err on the side of caution and try to guarantee at least 5C. Now you are protecting the pipes without necessarily heating the full slab. Normally you'd expect to see about 30C return water temperature, so its possible to safely reduce the floor emmissive power by at least 70% by this method.

edit ps

[This message has been edited by Alan Belson (edited 03-04-2007).]

Wood work but can't!
#75565 03/04/07 03:32 PM
Joined: Aug 2005
Posts: 265
Sixer Offline OP
Thanks for your responses. I'll be dealing with it this week and I'll let you know what the end result is.


"Will it be cheaper if I drill the holes for you?"
#75566 03/05/07 01:12 AM
Joined: Nov 2001
Posts: 52
KJ Offline
Junior Member
Shudder when i think this, but have you asked the heating pros yet,you may be able to heat by using a circulator wired to a different zone,and an aquastat for backup control.

#75567 03/05/07 06:37 AM
Joined: Jul 2004
Posts: 787
Member The Wall

Excellent source for information. Comparable to here.

Larry C

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