Hi everyone. This is my first post in here, as well as built my first pole barn, and first experience with in-floor heat. I have a 36x56x14.5ft r38 in the ceiling, R10 foam board in the walls with all seams glued and sealed and 2” under slab foam board. 1 zone of 8 loops of 1/2” pex at 250ea. Pump is on low speed. My combi boiler is a navien 80,000btu. Boiler has been working great. My supply is set at 95deg. And I usually have a 20ish degree difference between supply and return. My thermostat is set at 60, it’s a cheap Menard’s hydro smart unit. I’ve notice that the temp on my thermostat will get all the way down to 54 before kicking the boiler on. I haven’t found an adjustment for this on the thermostat. Is it normal for it to cool down this much?
Radiant slab heat thermostat question
- Thread starter jacobK
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75gmck25
Well-known member
House thermostats I've purchased in the past (Honeywell, etc.) usually trigger a call for heat at a difference of about 2 degrees from where the temp is set. A few are adjustable for the differential, but for most you just have to look at the specs and decide if you like it.
Fav Onefour
Well-known member
The basic hydro smart stats should have an offset selection. It looks like you are at the six degree differential. I'm curious if it is overshooting the stat once the slab builds heat. Move it down to four and see how run times change.
Slab heat is different than a forced air setup. Recovery takes more time. The single zone is a big chunk of mass to change temp. It can overshoot your settings a bit more. I'm not familiar with that exact boiler. I'm guessing it is not a modulating boiler. You may have gained run time efficiency through your thermostat differential offset. It may be just too much.
Your supply seems like a good setting and 20ish difference is doable.
If run times don't go crazy at four degrees then try for two. It doesn't sound like your setup would be a fast recovery setup prone to short cycling.
Slab heat is different than a forced air setup. Recovery takes more time. The single zone is a big chunk of mass to change temp. It can overshoot your settings a bit more. I'm not familiar with that exact boiler. I'm guessing it is not a modulating boiler. You may have gained run time efficiency through your thermostat differential offset. It may be just too much.
Your supply seems like a good setting and 20ish difference is doable.
If run times don't go crazy at four degrees then try for two. It doesn't sound like your setup would be a fast recovery setup prone to short cycling.
jblnut
ALLIANCE MEMBER
Yikes 6 degrees !! My house and shop in floor setups are set to 1f and they do great. I’m heating with an outdoor wood boiler now but haven’t changed a single setting from when it was all new and everything was running of my IBC boilers.
I set the shop stat to go off of the floor probe so things don’t go wild when the big doors open and the temp drops 4-5f in a hurry. Before the system would call for heat and the slab would way overshoot and it’d get warmer than needed and nothing would call for heat for hours.
I set the shop stat to go off of the floor probe so things don’t go wild when the big doors open and the temp drops 4-5f in a hurry. Before the system would call for heat and the slab would way overshoot and it’d get warmer than needed and nothing would call for heat for hours.
fitter30
Well-known member
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Chandler78
New member
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- Nov 26, 2024
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Did you happen to figure out your temp issue regarding the 6 degree difference? If so, what was the problem? I have spoken with Hydro-smart and haven't got anywhere with them. They keep on telling me to play with the thermostate. I have mine set on 70. It will drop to 66. Then it takes 10 hours of running before it gets to 71 and shuts off. Then it won't kick back on for almost 48 hours. My house is completely spray foamed at which I know helps. Any information would be greatly appreciated. Thanks
Have to remove thermostat from wall for access to to dip switches. Prop. /Conv. Try changing to the other one. Is there a junction box that the stat is mounted to? Insulate it might be getting a false temp.AUBE TECHNOLOGIES TH135-01 INSTALLATION AND USER MANUAL Pdf Download
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fitter30
Well-known member
Don't change things at one time. Baby steps and Wright down what you did. Then give it two days. Radiate takes awhile to settle down because of the mass. What water temp are you running still 95°? Lower it 5° see what happens. Boiler water temp differential?
Last edited:
Chandler78
New member
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- Nov 26, 2024
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I am running my boiler temp at 120. My return temperature is roughly 85. With a 4.2 gpm. I have 11 different loops little over 3000 feet of 1/2 tubing in 6" concrete.
fitter30
Well-known member
Normal design temp difference is 20° 1 gpm per 10k btu
Pump head 300' loops = 9' + 3-4' for manifolds and other piping if piped primary secondary loops. Have any wood floor coverings? Running any glycol brand and %. Start with lowering water temp 10° to 110°.
PWC Repair
Well-known member
I've been using a Tekmar with a sensor in the slab. Works GREAT and learns temp drops and run cycles to keep the shop the same temp all the time. I'll NEVER try to run a slab setup without one again.