Not.... I have the Garn jr. 2000sf of 3” concrete on top of 4” Dow sm shiplap with pex. It’s been -20’s C or -10 F here for more than a week, had the slab warmed up yesterday I thought. I have a mixing valve on that zone, usually I fire at 10pm so I have around 160* in the secondary and tempered down for the slab. At 8am the secondary is usually no lower than 120*. Well woke up this morning house was low 60’s, rads and in floor pep were cool, secondary at 80*. What the heck!! I thought with the warm slab it would cruise through the night, nope it apparently sucked ALL the heat from the system.