Under slab radiant temperature

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Baird M

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I currently have oil fired baseboard heat and want to heat a concrete floor in a 500 square foot room. My question is do I need to install an indirect water heater to do so or can I run another zone off my boiler and temper it? If so what is my best option? What about thermal shock to my boiler?
 

WorthFlorida

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Probably not if you are substituting the baseboard for floor heating and it currently can keep the space comfortable. Knowing the BTU output of the boiler and total heat load of the home will be needed to determine if the boiler can handle the load. How old is the boiler?

Are you installing a plastic grid and snap in the PEX tubing then cover over it with tile? To run another zone there are two ways, two circulators or one circulator with solenoid control valves. If you need to temper the heated water, it gets more complicated. If you want to do it as a DIYer, the floor part is easy enough, the furnace part you should get a company to make the modifications.

If you search this forum for user DANA, he has hundreds of post on how to calculate heat loads and many good points on old and new boilers.
 

Baird M

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Thanks. I have a 150,000 BTU boiler running 2 zones at 900 Square feet each. Using 1 taco 007 and a taco zone pack and valves. I previously made provisions for a third zone. I have all the pex the insulation etc.. figured out. My question is. How do I temper the under slab zone? If I am using a mixing valve and tempering with domestic water how do I avoid thermal shock?
 

Fitter30

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How can you temper with domestic water? Wheres extra water going? That link i posted shows some examples thats why ask question in the post. With 150k boiler it has to be short cycling.
 

WorthFlorida

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For floor heating the cool water returning from the floor is mixed the hot water going to the floor. The same as any tempering valve. What is your definition or concern of thermal shock and where?
 

Jadnashua

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You're going to need a manifold, as you should try to limit any single loop to a maximum of 200'. Otherwise, the heating will be uneven.

As said, run the return line to the cold inlet of the tempering valve.
 
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