Thermostat for in-floor hydronic heat

Henry_8

I have a 50+ year old house with heating pipe in a concrete slab and am looking for a thermostat for this type of system.

I did a search but did not find any information specific to my case.

I have tried several different makes and they don't handle the long lead/lag time of slab heating very well. I did try Wirsbo and they seem to work better than most, but I have had two and both failed in one way or another.

In an internet search I came up with a Honeywell T8775A,C that has a reference to hydronic heat in the instructions. Anyone have any experience with this thermostat in slab heating, or can recommend something else?

Henry

Steve Eayrs

Henry, You may want to.......

consider looking closer at the actual piping and if you even have any kind of outdorr reset, mixing controls, or not. There are a lot of thermostats out there that would work fine, but based on your information, it is very possible that you problem has more to do with the temp. of the fluid running through your floor, than it has to do with which thermostat you use.

At the same time, I prefer certain thermostats for radiant floor heat, but they will only operate right if they match the logic/plan of the rest of the system.


Steve

Steve Eayrs

One more thing......

Have used a lot of Wirsbo/Tekmar thermostats/controls, and have found them to work better than more for radiant floor. If you have had problems with the operation or failure of yours I would bet it is either related to an incorrect install or other things in our system.



Steve

Henry_8

> Have used a lot of Wirsbo/Tekmar

> thermostats/controls, and have found them to work

> better than more for radiant floor. If you have

> had problems with the operation or failure of

> yours I would bet it is either related to an

> incorrect install or other things in our system.

> Steve



Hi Steve, thanks for the quick reply. I will try to respond item by item.

“consider looking closer at the actual piping and if you even have any kind of outdorr reset, mixing controls”.

There is no outdoor reset or mixing controls. It is a simple straightforward one zone system with a Polaris water heater.
“ it is very possible that you problem has more to do with the temp. of the fluid running through your floor”. I can control the water temperature at the Polaris and it is usually set between 100 and 130 degrees. I vary this depending on the outside temp. to try to maintain a 85 degree floor surface temp.
“There are a lot of thermostats out there that would work fine”. AND “I prefer certain thermostats for radiant floor heat”. That’s what I’m looking for. What can you recommend?
“Have used a lot of Wirsbo/Tekmar thermostats/controls, and have found them to work better than more for radiant floor. If you have had problems with the operation or failure of yours I would bet it is either related to an incorrect install or other things in our system.” The first Wirsbo thermostat controlled the heat better than anything I have tried. It worked fine for two winters and then developed a mind of its own, switching to heat on a hot summer day (not because of a power failure). I returned it and got a heat only model and that one developed a tendency to read three degrees high. I am returning that one next week for a refund.
I would appreciate any recommendations you have.
Henry

Henry_8

> Have used a lot of Wirsbo/Tekmar

> thermostats/controls, and have found them to work

> better than more for radiant floor. If you have

> had problems with the operation or failure of

> yours I would bet it is either related to an

> incorrect install or other things in our system.

> Steve

Henry_8

> consider looking closer at the actual piping and

> if you even have any kind of outdorr reset,

> mixing controls, or not. There are a lot of

> thermostats out there that would work fine, but

> based on your information, it is very possible

> that you problem has more to do with the temp. of

> the fluid running through your floor, than it has

> to do with which thermostat you use.

>

> At

> the same time, I prefer certain thermostats for

> radiant floor heat, but they will only operate

> right if they match the logic/plan of the rest of

> the system.

>

> Steve

Unknown

one question:

are you fiddling with the thermostat settings?

High mass radiant works best if you set it, and leave it. If you are trying to do setbacks or anything like that it requires more than a simple thermostat adjustment to acheive.

Not to say that high mass doesn't have other issues if improperly controlled, just trying to rule out the easiest possible problem you may be having!

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Henry_8

Hi Steve, thanks for the quick reply.

There is no outdoor reset or mixing controls. It is a simple straightforward one zone system with a Polaris water heater and I control the water temperature at the Polaris. It is usually set between 100 and 130 degrees and I vary it depending on the outside temp. to maintain a 85 degree floor surface temp.

You say “There are a lot of thermostats out there that would work fine”. AND “I prefer certain thermostats for radiant floor heat”.

That’s what I’m looking for. What can you recommend?

Henry

Henry_8

Hi Steve, thanks for the quick reply.

There is no outdoor reset or mixing controls. It is a simple straightforward one zone system with a Polaris water heater and I control the water temperature at the Polaris. It is usually set between 100 and 130 degrees and I vary it depending on the outside temp. to maintain a 85 degree floor surface temp.

You say “There are a lot of thermostats out there that would work fine”. AND “I prefer certain thermostats for radiant floor heat”.

That’s what I’m looking for. What can you recommend?

Henry

Henry_8

Wirsbo thermostat

The first Wirsbo thermostat controlled the heat better than anything I have tried. It worked fine for two winters and then developed a mind of its own, switching to heat on a hot summer day (not because of a power failure). I returned it and got a heat only model and that one developed a tendency to read three degrees high. I am returning that one next week for a refund.

I would appreciate any recommendations you have.

Henry

Henry_8

Response to Rob.


> are you fiddling with the thermostat


No


> best if you set it, and leave it.

Thats basically what I do.


> If you are trying to do setbacks


No setbacks

Unknown

wow. you actually have to manually vary the water heater setting?

leave it at 130 and put in a tekmar thermostat. It will cycle your zone on and off more frequently as it approaches its room setpoint. It's not mixing control, but short of repiping the entire system it's the next best thing.

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Weezbo

henry,it sounds like you have to control it better.......

radiant that is bouncy means you are really likely running to high a temp ,or you are picking up solar gain or it has a set back feature out of sync with the real world or the loop lengths are too long....some stuff we dont have a lot of control over solar gain can be ameliorated,too high a temp control water temps down ,setback change the on off settings,long loops reconstructive efforts might help.

Henry_8

> wow. you actually have to manually vary the

> water heater setting?

>

> leave it at 130 and put

> in a tekmar thermostat. It will cycle your zone

> on and off more frequently as it approaches its

> room setpoint. It's not mixing control, but

> short of repiping the entire system it's the next

> best thing.

>

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