Optimizing the Slab Radiant Heating System

[fitter30]

Any condensing boiler needs return water under 140° and the colder the better for efficiency. Above 140° efficiency drops to 87% condensation stops. Boiler gets it efficiency from running the condensate through another heat ex changer. Their exhaust can be cooler than the exhaust that's how they can use pvc for exhaust. The only time i used a protection loop the cast boiler was for a process or fed a outside air coil. House usually doesn't have a zone that is big enough to push enough cold water back to it.

 

[600SL]

OK you guys are getting a little too technical for me but yesterday I had to turn off the boiler to allow it to cool. So that I would get good contrast when looking at it with a FLIR infrared camera. For that I actually had to turn the temperature back up to the default 180F/130F. With that done I now turned the setting back down to 105F/86F. I didn't want to go lower than 105F since 95F is the absolute lowest I can set at. As of now the boiler temp is running at 95 with both zones currently calling for heat and the manifold is at 90F in 75F out. Room temperature was 55F and climbing to 58F thermostat settings. Outside temp is now 29F. I will need to wait another day to let things settle out but I think they are looking better.

 

[PoorUB]

With that done I now turned the setting back down to 105F/86F.

If it heats in cold weather at that 105 max temp I would leave it there, but you might have to bump it up to 120 max temp. Chances are, once the floor stabilizes the boiler will modulate down and run on low fire any way, but in severe cold it will ramp up if needed. Just something to watch out for.

 

[600SL]

If it heats in cold weather at that 105 max temp I would leave it there, but you might have to bump it up to 120 max temp. Chances are, once the floor stabilizes the boiler will modulate down and run on low fire any way, but in severe cold it will ramp up if needed. Just something to watch out for.

Unfortunately I missed the real cold days, but Saturday might should get down to 15F.

 

[600SL]

We had a fairly quick drop in temperature to 12F this morning. Room temperatures both held up as set to 57F. Inlet temp was running ~ 102F outlet ~76F. I'm still a little concerned about the Delta T inlet to outlet being high at 26F but it really is only about 36 hr since I turned the system back on. Not likely I will see temps down below 20F this year.

 

[Mr onetwo]

Guys....I have not seen anyone mention Primary/Secondary piping.This boiler must be piped up exactly as shown on pages 40 and 41 of the installation manual.This is basically a hot water heater that can be used as a combi unit. Set the min to 135 and the max to 145. There has to be a mixing valve on the domestic hot water.This system will not condense much at those parameters, but will be fine. I would not hook up the outdoor sensor...just set the floor temp to 100 degrees and air temp thermostat to whatever...58 I think. If you have feed water hooked up to the system, test the glycol and then SHUT off the ball valve.A photo of the system would be helpful. Convert it to a pdf from a jpg and post it.

 

[600SL]

Guys....I have not seen anyone mention Primary/Secondary piping.This boiler must be piped up exactly as shown on pages 40 and 41 of the installation manual.This is basically a hot water heater that can be used as a combi unit. Set the min to 135 and the max to 145. There has to be a mixing valve on the domestic hot water.This system will not condense much at those parameters, but will be fine. I would not hook up the outdoor sensor...just set the floor temp to 100 degrees and air temp thermostat to whatever...58 I think. If you have feed water hooked up to the system, test the glycol and then SHUT off the ball valve.A photo of the system would be helpful. Convert it to a pdf from a jpg and post it.

It took one picture today. DHW is not connected and turned off.

 

[Sumboodie]

Boiler is a LAARS FT Series Gas Condensing Combination Boiler. The default max temp is set to 180° F but it seams to be running at around 150 and at the manifold inlet I'm seeing ~140. But I did see as high as 175 when I first started. So will that max temp in the boiler setup, should that be reduced, I just assumed that was a safety limit and maybe the running temp will reduce as the slab comes to temperature.

Way too hot. 130* max.

 

[Sumboodie]

The minimum I can set this boiler to is 9F above the minimum. Lowest possible minimum is 86F therefor the lowest mas is 95F. The garage is not leaky at all and. insulation is about R15 walls, R19 ceiling with 3 insulated garage doors.

R19 ceiling is terrible. Should be 2x last minimum, 3x that ideal.

 

[Mr onetwo]

If it is wired correctly the the min/max has nothing to do with the floor. The internal pump/primary loop will run between min max on call from tstat/secondary pump.Get rid of the backflow preventer and prv. Just fill system when necessary with hose fitting watching the pressure...shouldn't exceed 20 psi cold. Fill only with premixed glycol.

 

[600SL]

R19 ceiling is terrible. Should be 2x last minimum, 3x that ideal.

R19 is the highest you can get for the steel building kit. Anything else needs to be added between the pulins. I may go that in the future.

 

[600SL]

Way too hot. 130* max.

Currently running 105F/86F. So far no trouble keeping up down to 12F outside temp. It hold temp and even cycles off.

 

[600SL]

If it is wired correctly the the min/max has nothing to do with the floor. The internal pump/primary loop will run between min max on call from tstat/secondary pump.Get rid of the backflow preventer and prv. Just fill system when necessary with hose fitting watching the pressure...shouldn't exceed 20 psi cold. Fill only with premixed glycol.

Pressure is ~ 16 cold. Goes up to ~ 18 hot. Glycol is premixed. What is the backflow preventer and prv and why do I want to get rid of them.

 

[Kezorm]

Currently running 105F/86F. So far no trouble keeping up down to 12F outside temp. It hold temp and even cycles off.

Simple answer is that if it's cycling on and off - running less than 100% of the time, then your water is hotter than it needs to be (less efficient than it could be).

I recommended settings here - https://www.garagejournal.com/forum...-radiant-heating-system.542817/#post-11040727

If you ever notice it running 100% of the time and not holding room temperature, then the water is too cold.

 

[Mr onetwo]

Pressure is ~ 16 cold. Goes up to ~ 18 hot. Glycol is premixed. What is the backflow preventer and prv and why do I want to get rid of them.

Because you do not want to feed 100% water automatically into a 40% glycol system. The mix needs to be tested once a year and replenished if necessary by pumping premixed glycol thru that port with a transfer pump.System should be flushed and glycol replaced every 5 years. Because it should not be connected directly to a source of domestic water you do not need those parts.....just a ball valve and a hose thread with cap. https://www.supplyhouse.com/Webston...-A-Drain-Full-Port-DZR-Brass-Ball-Valve-w-Cap

https://www.amazon.com/VEVOR-Transfer-Portable-Electric-Connectors/dp/B0C3VTTYSS?tag=atomicindus08-20

 

[600SL]

Because you do not want to feed 100% water automatically into a 40% glycol system. The mix needs to be tested once a year and replenished if necessary by pumping premixed glycol thru that port with a transfer pump.System should be flushed and glycol replaced every 5 years. Because it should not be connected directly to a source of domestic water you do not need those parts.....just a ball valve and a hose thread with cap. https://www.supplyhouse.com/Webston...-A-Drain-Full-Port-DZR-Brass-Ball-Valve-w-Cap

https://www.amazon.com/VEVOR-Transfer-Portable-Electric-Connectors/dp/B0C3VTTYSS?tag=atomicindus08-20

I'm at a loss with this. I have a new premixed solution using Cryo-tek 40% premix. I have valves like you show all over the place and I used a pump like you show to pump in the fluid. DHW is not connected at this time but it will be in the near future but it will be and that part of the system to be connected to the domestic water supply from my house. Those two systems have no way of mixing.

 

[600SL]

Gentlemen at this time the system is running fine at least good enough to be able to heat up the floor so I could take a picture of it with a FLIR camera and layout where I can drill the floor for a lift. It will also keep me comfortable until the spring when my cousin who designed the system can get here and put the final tweaks on it.

I appreciate everyone's help and just would like to say thank you to all.

 

[Mr onetwo]

Just keep the valve closed to the makeup water feed so it can't put water into the floor without your knowledge.