Does it pay to turn down the heat at night when you have a radiant-floor heating system? David Meiland and a heating contractor are having trouble seeing eye to eye on that question.
Meiland says the house they’re discussing is a slab-on-grade with R-10 insulation below and PEX tubing cast into the slab. In another part of the house, the floor is framed, with PEX installed below in tandem with aluminum plates that help distribute the heat. The boiler is a 30-kW electric model with an outdoor reset.
In a Q&A post at GreenBuildingAdvisor, Meiland writes, “The heating contractor advised the homeowner that setting the night-time thermostat temperature too low would cause the system to work very hard in the morning to get the slab back up to temperature, and therefore waste energy.
“My opinion is that lowering the setpoint at night is a good thing, as the system will put fewer BTUs into the house, saving energy. When the system ramps up in the morning, it will reheat the slab without any loss of efficiency. Fewer total BTUs will be put into the house.”
Meiland thinks the heating contractor has it wrong, confusing a period of high demand in the morning with low efficiency.
That’s the focus of this month’s Q&A Spotlight.
High-mass floors respond slowly
While there is a mix of flooring types in the house, several readers pointed out that the high mass of a concrete slab will not change temperatures very quickly — and that has a bearing on the practicality of turning down the heat at night.
Cramer Silkworth, for example, writes that if the house is well insulated, its occupants may not experience an overnight drop in temperature even with the thermostat turned down. “The…