Another Radiant heat question

Hey guys. I finally got my radiant heat 100% up and running for my detached garage this past wknd after replacing the mixing valve and getting the air pockets out. Now my question is once the garage floor heats up to temp and turns the circ. pump off the thermostat doesnt call for heat again for 6-8 hours because of the floor radiating heat and the water in the slab cools down and it puts one hell of a load on the boiler until it satisfies the thermostat again. The boiler takes probably 45 minutes to get everything back up to temp when the garage zone is calling

1st question.- I currently have a 1" pex feeding my 1 1/4" manifold and a spare 3/4" supply and return pex available. Would it help if I added the extra flow from the 3/4" pex or

2- should I look into a flat plate heat exchanger to help warm the return water from the garage zone?

Thanks everyone. I appreciate everybodys help

Hey Matt, what temperature is the water that you are sending out to the floor? My first thought was that it was too warm and causing the cycles you describe. If you adjust the mixing valve to a lower temperature the circulator should run longer and shut off less often. A mixing valve with an outdoor reset control does this automatically, but that is another story.

Another question - How low does the S260's temperature get when your garage zone kicks on?

Does your thermostat have an adjustable differential, if so, lower the differential to have shorter run times more frequently. Did you use one of the 3 speed pumps, might be able to tinker with that. And as asked before, what temperature do you temper the water too ?

The garage zone is at 125* and the return is coming back at about 95*. I noticed this morning my boiler temp was down around 150*. My circ pump is a grundfos 15-42 1 phase no adjustment and the thermostat is one of the old rotary ones.

Maybe I should invest in a newer programmable thermostat. Does the temp drop in the boiler scare anyone else or just me? Or is this pretty normal?

chevymatt wrote:The garage zone is at 125* and the return is coming back at about 95*. I noticed this morning my boiler temp was down around 150*. My circ pump is a grundfos 15-42 1 phase no adjustment and the thermostat is one of the old rotary ones.

Maybe I should invest in a newer programmable thermostat. Does the temp drop in the boiler scare anyone else or just me? Or is this pretty normal?

125 deg. is the upper end in my opinion. Jack the temp down to 115 deg. f. for starters. You may have to go lower yet, say to 110.

As previously questioned by Rob R., the slab is storing way too much heat and releasing it when the thermostat is satisified.

Radiant systems are best when they react slowly and that is done with lower water temperatures.

What type of mixing valve do you have? Some only allow so much hot water mixed in at a time to prevent all the cold water dumping at once. You may want to look at a floor thermostat that react with tempeture changes in the slab. Other choice that I have seen is the use of outside sensor thermostats the antispate the change in Temp. Hope this helps