Any one with experience with monolithic cement slabs or/and radient heated cement

[kutter52]

I'm getting real 1/2 PEX-A 1000 ft & planning 4 loops around 225-250 ft ea, That is fairly dense in a 24 x 36 ft slab. The thermostat will control the heat input from the boiler. Should I have the circulation pump running 24/7 to avoid cold spots freezing? Or should I run some glycol in the water or both? And something should monitor the temperature so the boiler won't try to heat once it hits maximum temperature. Will the boiler have that control?

 

[CalG]

The boiler should have the control to limit over heating. But you might consider a multi zone control unit to interface the thermostat and circulators. The floor thermostat just turns the pumps off and on. After that, the boiler control tries to maintain boiler temps.. A mixing valve in the boiler output controls the circulating water temp.

Perhaps you have selected the boiler already, but domestic hot water heaters make good hydronic heat sources.
One thing to be aware of , is that if the floor water circulates directly through the boiler heat exchange, the thing is going to sweat like crazy until all that floor water warms up.
A mixing valve to allow the boiler to stay hot is required. This will in no way reduce the the heating capability or increase the warm up time, but it will make the boiler a lot happier.

 

[kutter52]

CalG,
How does a mixing valve work when the system does not take more water? Do I plumb the returning water to the cold side & boiler water as the hot? I guess that makes sense. But what feeds the boiler? That would need to be returning water as well. I plan to put an expansion tank on the circuit as well. Will I need to add water from time to time or have an active supply to it?

I plan to just have a circulator pump taking return water and sending it to a multi tee feeding the 4 loops. Since the loops are similar length I don't I need to individually control them. Someone said not to cross any PEX lines but I do not see the problem with that and I want to enter and exit the slab from a common area where my boiler will be located so some returning "cooler" lines will cross over or under other loops. What would the problem with that be?

 

[aeblank]

The mixing valve mixes in the cold return water from the loop with the hot water from the furnace.

all this makes me bummed I still don't have my floor hooked up in my 32x60 garage. Maybe THIS summer I'll get it going....

 

[kutter52]

The mixing valve mixes in the cold return water from the loop with the hot water from the furnace.

all this makes me bummed I still don't have my floor hooked up in my 32x60 garage. Maybe THIS summer I'll get it going....

And the water to feed the boiler? Split off from the return water?

 

[aeblank]

hot goes into the mixing valve, cold goes back to the boiler. The mixing valve Ts into the return to steal some water.

http://hydronicpanels.com/wp-conten...old-Station-with-Tempering-Valve1-300x237.jpg

 

[kutter52]

i just got my Uponor Design manual today. They describe a motorized 4 way butterfly valve that passes your return water to supply or turns to divert water to the boiler and allow hot water from the boiler to pass into the stream. I will research these.

 

[Sprinklerman]

I have helped on 2 installations of radiant floor heating , first you NEED the foam insulation underneath , plain and simple doing it without the foam is a waste. One that helped on was a 16 wide by 40 ft long garage with 16 foot ceilings . It is always comfortable , it uses about 200 gallons of oil a month . The shop is used 10 hrs a day 6 days a week ,but its a heating oil company and they burn oil they get from tank pump outs. The second is a 30 by 26 with 14 ft ceilings , its attached to a house and it runs from the house boiler as a seperate zone , he keeps the tsat at 50 degrees his oil consumption went up 50% . ( both are fully insulated shops) My garage is 36 by 42 with a oil furnace , I only fire it up when needed , I went thru 75 gallons this winter working 3 days a week .

 

[kutter52]

It looks like home Depot.com has the best price I found for 2" polystyrene 25 sheet in 4' X 8' They carry Owen Corning's 2" Foamular 25 at 33.88 a sheet I'll need 34 of them to do the floor & around the perimeter of the footer. It will be a mono pour slab & I will let the bottom of the footer rest on the crushed limestone. I plan to use a natural gas fired boiler, that I'll need to plumb out of my house. I'll need electric & water as well, although it concerns me how I'll bring that up through a floating slab. What if I brought all three up through the slab inside of a 4" piece of pvc where they will have some wiggle room if the slab moves a 1/4 inch or so. I'd be good for an inch or so of movement inside the middle of a 4" PVC. I can use fiberglass insulation around the pipes & conduit.

Found the motorized 4 way: Danfoss 193B1531 in 3/4 & 193B1533 in 1". The 1" is only 20 bucks more than the 3/4 with a Cv of 11.7, but with the actuator they'll get me $300. Uponor says to use one to keep the boiler from short cycling. So I'll bite the bullet and pony up. I'll call Danfoss tomorrow to see what else I need. A temperature probe I'm sure & their info sheet shows a "controller" whatever that is. Unless, of course, they're referring to the motor controller that uses the temperature probe for an input. Oh, I must pay to play.

 

[Paddy]

kutter52,

Our all concrete home has radiant heat, and it works very good. But it might not be the best for a garage unless you plan to use it all the time. Radiant holds the heat well but also takes time to heat up. You would have to use some sort of antifreeze if you shut off the heat. Otherwise you heating life.

Insulation is key. I'd insulate the stem wall as well. In the '70s the trend was to pour the slab on a big bed of sand to let the huge mass hold heat. The problem was no one did the math. It took so many Btu's to heat the sand. They were really just heating the earth