Concrete floor as heat storage device

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New Member
Hearth Supporter
Oct 2, 2008
Southern VT
We are about to purchase a wood fired boiler for the house we just moved into. Got some good ideas on boilers but curious about storage. The prior owner put radiant heater pipes thru the garage floor. Let's say there are 40,000 lbs of concrete in the floor. The garage is very well insulated. Does this seem like a practical way to store excess heat? In addition to the earth below it looks like it could be a geothermal heat sink and source.

Speaking of geothermal. Has anyone filled a water filled heat sink with gravel or pea stone to improve the heat storage capacity? Not sure where to find the heat capacity of stone versus water but a stone stays hot longer than water.

Thanks for all Cobble
There have been threads on this subject before you could do a search for and read through. The short answer is that water is the most efficient at storage because btus can transfer more quickly in and out of water than stone, sand, gravel, etc.
Thanks for the thoughts on this issue. How hot does geothermal storage get up to? Don't think I could get the entire 40,000 lbs up to 180. Maybe 80 or 90 degrees would be more reasonable. Would that be warmer than return water from my baseboard heat? Thanks Cobble
Floors don't really work well for usable storage, they can't be warm enough to store heat for baseboards. They make great dump zones for overheat, and they work well extracting the most out of hot water storage because they can be quite cool and still heat the house.
This needs to be in the FAQ sticky that we don't have. I had the exact same thought when I started designing my system.

Surprisingly, stone stores less heat per pound and per cubic foot than water does. Even if it were as easy to get the heat in and out, and even if you could reach 180 or more safely, you would be able to store more heat in a cubic foot of water than a cubic foot of stone or concrete.

Water is miracle stuff. Nice that it's so cheap.
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