floor heat temp probe placement

t300

On my garage floor heat zone the Emerson controller temp probe is zip tied to the return piping (probe on pipe, wrapped by piece of carpet then zip tie). No other tstat. Canadian cold winters down to -30c, I want to keep the garage at 15c ambient. Is it standard to have the probe installed in this method? Just turned on the floor heat and as expected the return piping temp quickly gets to the 20c setpoint and then valve shuts as expected, only to cycle again shortly after. I forsee it cycling a ton for a few days before the slab gets up to stable temp. On winter startup, should I be raising the setpoint way over what I want, like 25c or 30c, until the slab temp catches up then turn it back down to 15c ish?

I was thinking of taking the probe off the pipe and hanging it in ambient air until the garage stays around 15c then putting it back on return pipe. Good idea? Terrible idea? Does it matter?

hot_rod

Most common is a thermostat on the wall.Sometimes a sensor is installed in the slab to maintain a certain floor temperature. Do you have glycol in the system. Garage slabs with tubing near the door can freeze quickly if something fails, or a day long power outage.

Derheatmeister

I am Guessing that you are talking about a slab sensor ?
If so it should be installed in the slab between the tubing to sense the slab temperature. If this was not done then a IR camera could be used to locate the tube and a hole could be drilled for the proper sensor install.

RascalOrnery

Could someone clarify when a slab sensor is superior to an air temperature sensor? Doesn't a slab sensor just tell you what your output is, rather than indicate whether the occupied area is comfortable or not? How does a slab sensor not permit overheating?

hot_rod

Different uses for slab sensors, it could be a freeze alarm function, Or it could be used to limit the slab to maybe 70 degrees

If it is a space that you work in or spend  time in, an air sensing t-stat us most common

EdTheHeaterMan

RascalOrnery said:

Could someone clarify when a slab sensor is superior to an air temperature sensor? Doesn't a slab sensor just tell you what your output is, rather than indicate whether the occupied area is comfortable or not? How does a slab sensor not permit overheating?

If you maintain a minimum or maximum floor temperature, then a Slab Sensor is helpful. If you are doing an outdoor reset system you may want to know the floor temperature and adjust that floor temperature based on outdoor temperature. However I agree with @hot_rod, if you want to maintain a specific room temperature, You should use the room temperature thermostat for that function.

I know of one snow melt system at a car wash that uses slab sensors that bring on a waste oil boiler even if the place is closed. If there is precipitation and the slab is at freezing, the boiler starts sending heated water to the slab. A room thermostat placed outside would not be the best use for that situation.

t300

Thanks for the comments everyone. FYI its a Emerson 16E09, I read the manual and reviewed the install and verified it is simply for temp setpoint. Standard NTC sensor. Nothing in the slab. I'll just play with the setpoint for now and wire in a air tstat when I get a chance.

hot_rod

You will reduce the operating cost with an air sensing thermostat also.

With a slab or pipe sensor only, on mild days the slab could be putting heat into the space when it may not need it. It is trying to reach a setpoint temperature regardless of what the load is. Or isn't.

Another control logic is to use a stat that has both air and sensor inputs. Then you can either limit the slab temperature, or put a not to drop below temperature. We use those on bathroom floors that may run year around.