Hydronic Radiant Slab Heating – Not As Efficient As Hoped
I’ve compared my winter heating bills between my old home (2-story 1450sqft) and new home (1-story 1550sqft) and the differences are a bit surprising. The old home had tall ceilings and an undersized furnace, it seemed like it was running all the time to keep the house at 70º. The “new” home has hydronic hot water radiant in-slab heat via a commercial hot water heater, but the gas usage (which are only used to heat hot water) is nearly DOUBLE. I thought hydronic radiant heat was supposed to be efficient?
My home inspectors said the hydronic radiant heat was in good working order…but these bills have me worried he missed something.
The new (to me) home was built in 1998, is a slab foundation, and the inspector was not able to determine insulation under slab or depth of radiant tubing in slab, although his thermal imaging looked normal. Good clear radiant lines throughout the house. The WIRSBO control system utilizes old school circa 1998 independent loop thermostats with floor sensors and a single Grundsfo circulating loop pump. Is it possible that single pump is too small for 1550sqft and four independent loops?
Now, granted, the difference in gas bills isn’t too bad ($75 current furnace vs $135 hydronic) but I’m a bit dismayed that in our case the commonly marketed “efficient” hydronic radiant heat is not so much.
One thing that confounds me is that I have no idea how the slab was insulated, and it very well may not be. Is there some way of inspecting the slab insulation via borehole? Would those costs even be worth it?
Other things to check and troubleshoot?