Raidiant Heat from a Slab

Ericjeeper

Does the window wall face the south?If so you will reap a plenty of gain from the sun. My house is heated with in slab radiant. and my water temps call for 95 and under. But my envelope is pretty tight.. My floor temps run pretty much the same as room temp. If the floor reads 72 degrees it is basically what the room temp is. except on days when we entertain a group of guest.. Then the floor is 70 and the room will raise to as high as eighty.. I am talking a room that is 22x40. so lots of bodies will bring the room temp up.Is there any way to increase the amount of insulation?>
What are you using for a heat source?

Mike S

Heat Gain from a Slab

Hello to all,
As a first time do it your selfer, I'm not sure how much heat gain I can expect from a 20x20 slab of concrete with 400 feet of 3/4 pex burried in it. I know from reading some of Dan's books that with 3/4 pipe I can move 4 gallon a minute. Using a 20 degree temperture differential that would translate to 40000 btu's I could pump into the slab, but my question is how much heat will a slab generally give off. My concern is with a 21,000 btu heat loss in that particual space on the coldest day of the year (0'F) I'll need some amount of supplimental heat but don't know how much.
Thanks for any advise
Mike S.

Tim Doran

Manufacturer

How thick is the slab, how deep in the slab is the tubing, what is the spacing, what is the supply water temperature, are there floor coverings? 21000 btu/h in 400 sqft seems a bit high! The manufacturer/vendor of the pex and components should be able to help you out with all of the design and application calculations.

Tim D.

Mike S

Heat Gain from a Slab

Thanks for the reply. The slab is 4 inches thick, and the tubing is burried aproximatly in the middle. The floor covering will be tile and the water temperture I'm assuming will be around 120 degrees. The manufactuer claims 50 btu's per foot in a slab application. 21000 btu heat loss is for the coldest day in a room with lots of glass and a high cathedral ceiling. My understanding is to to maintain a floor temperture aroung 85 degrees. My question is how much heat (btu's) aproximatly can I expect to be added to the room.

Tim Doran

Room set point

To get 50 btu/sqft with an 85f surface temp you would need an approximate room set point of 60f. Seems a bit cold.

Tim D.