When should I turn my in floor heat on for the Season?

Fall is here! When do most of you turn your boiler on? my floor temp is still at 70 degrees. Last year I made the mistake of putting my system on a NEST thermostat that just about broke me for LP fuel because if i wasn't in the shop for a few days the thermostat would allow the temp to go down to like 45 degrees (safety level) then when i walked in it would sense i wanted heat, and the dam thing would run for like a day to get the heat back up from 45 to 65. This year i think i am gonna set it at 60 and leave it!

A lot of variables. I have a Nest thermostat for the HVAC but in the winter I use the thermostat hooked into the hydronic system that reads from a temp sensor buried in the slab. Of course here in NC I would be turning on the floor heat later than you but I found that setting the slab temperature to 60 to 65 worked well. Do you have a sensor in the slab and if so what is the temp of the slab now?

Geography matters as does weather patterns...which unfortunately are affected by changing climate conditions that make prediction hard. In floor radiant can be a challenge because it takes awhile to stablize and once it's on, you want to leave it on. I'd suggest you judge based on night time temp patterns in the one to two week forecasts for your area.

Currently we turned off the cooling but during the day our house is getting up to 80 in NJ and we have to run the ac before bed. I dont have in floor but Id say once the house is consistently below 66 degrees you may want to think about switching it on. The house itself will be safe to lower temps but its really about comfort. Depending on your boiler it should be automated to turn on when you call for it.

David, my question and point was that I wouldn't depend on a wall mounted thermostat to determine how warm you make the floor. It will mostly monitor the air temperature by way of convection after the floor heats the air. There may be some radiant heat hitting the thermostat but some of that will be absorbed by the cover. I find that I am comfortable in the shop with lower air temps by being subjected to the radiant heat coming from the floor. Setting the wall mounted thermostat to a typical comfort level will probably make you unnecessarily use more floor heat than needed for comfort. You may be way ahead of me and know all this and I may be mis-interpreting your question.

Turn it on now. Keep the floor at 70 degrees (or whatever your target is). If it doesn’t need to run it won’t.

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Originally Posted by Allan Dozier

David, my question and point was that I wouldn't depend on a wall mounted thermostat to determine how warm you make the floor. It will mostly monitor the air temperature by way of convection after the floor heats the air. There may be some radiant heat hitting the thermostat but some of that will be absorbed by the cover. I find that I am comfortable in the shop with lower air temps by being subjected to the radiant heat coming from the floor. Setting the wall mounted thermostat to a typical comfort level will probably make you unnecessarily use more floor heat than needed for comfort. You may be way ahead of me and know all this and I may be mis-interpreting your question.

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The question I was trying to ask was.. Do you turn the floor heat on before the slab temp falls below what the "hold temp" will be? In my case I set my thermostat to 60. I speculate I would want to start the heat up before the slab gets below 60 degrees.

Sorry but I am still dense. Is the thermostat that you set to 60 measuring air temperature or measuring the slab temperature from a sensor in the slab? I was assuming it was measuring air temperature which I thought was not ideal. But if you don't have a sensor in the slab then I would do the best with what you got.

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Originally Posted by Allan Dozier

Sorry but I am still dense. Is the thermostat that you set to 60 measuring air temperature or measuring the slab temperature from a sensor in the slab? I was assuming it was measuring air temperature which I thought was not ideal. But if you don't have a sensor in the slab then I would do the best with what you got.

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My radiant system measures both ambient and slab temps. If either goes below the set amount the system turns on. There’s another sensor which measures outdoor temps which I don’t use that is designed to keep the system from swinging wildly as there’s a lag in temp response with radiant floors.

I haven’t turned on my heat yet but plan to today. Our overnight lows have been in the low 40’s, shop temps have been in the low 60’s first thing in the morning.

Jeff

Do you let in air from outside via an overhead door or such?

Not an issue for me at the moment, but in my last shop it was condensation that determined the temp I kept the shop. Which changed over the course of the season.

The worst was when the equipment was 'cool' and I opened the overhead door and a rush of warmer humid air came in and condensed on every metal surface.

I just turned mine on last weekend, my slab is still warm so I figure why not keep it that way. It takes alot of fuel to heat a cold slab. I'm hoping my recent mini split install this summer will help my heating cost this winter. I know I sure like the affordable cooling it provided this summer.