Floor heating is the most flexible heater in your house

Resistive floor heating is in most Estonian homes and most of it runs dumb. The slab is essentially a thermal battery — heat it during cheap night hours and the temperature barely moves until morning. Price-aware scheduling captures spot-price spreads that are completely invisible to the room thermostat. The most flexible heater in the house, hidden under the tile.

Almost every Estonian home has electric underfloor heating somewhere. Bathrooms invariably. Kitchens often. New builds, the entire ground floor. It is so familiar it is invisible — which is roughly why nobody talks about it as one of the best flexibility assets a home owns.

It should be talked about that way. A heated screed floor stores hours of warmth. Heat it during cheap hours and the room stays warm for four to eight hours after, even with the circuit off. That is a thermal battery sitting under the tile, with a discharge curve measured in hours rather than minutes.

Resistive floor heating is everywhere here. Bathrooms almost universally, kitchens often, entire ground floors in new builds. Typical loading is 100 to 150 watts per square metre, so a heated kitchen draws as much as a Level 2 EV charger, and a whole-floor install in a new house can pull 6 to 8 kW. That is real load, and it is sitting under the tile doing nothing clever about day-ahead spot prices.

Why the floor beats the heat pump for short-window arbitrage

A heat pump has a compressor that prefers long, steady runs. Cycling it every hour to chase cheap quarters of the day shortens its life and tanks its seasonal efficiency. A floor-heating circuit has none of that baggage. There is no minimum runtime, no defrost cycle, no oil to settle. A relay clicks, current flows, the wire warms up. You can switch it a hundred times a day and nothing complains.

Combine that with the slab itself. A heated screed is essentially a battery for low-grade heat, with a discharge curve measured in hours rather than minutes. Heat it one or two degrees above your comfort target during the 02:00 to 05:00 trough, let it coast through the 07:00 to 09:00 morning peak, top it up again midday if solar pushes prices into the floor. The room temperature barely wobbles. The bill does.

Efficiency is the obvious objection. A heat pump turns one kilowatt-hour of electricity into three or four kilowatt-hours of heat; a resistive floor turns it into exactly one. That is a 3 to 4x penalty on paper. In practice the spot-price spread between a cheap winter night and an expensive winter morning is routinely 5 to 10x, which more than covers the gap when the floor is used as a comfort layer rather than the primary heat source. In homes without a heat pump, smart-controlled floor heating can quietly shoulder a meaningful share of the load.

The mechanics are unglamorous. Most modern floor-heating thermostats from Heatit, Devi, OJ Electronics, Uponor and Microtemp speak Z-Wave, Modbus or OpenTherm out of the box. Older installs with a dumb dial thermostat are even simpler: drop a smart relay in the junction box upstream of the thermostat, leave the thermostat at its comfort setpoint, and let the relay decide when current is allowed through. Coordinate across zones so you do not fire every circuit in the house at the same minute and trip the main fuse, and weight the schedule with a weather forecast so the slab is already warm when a cold front lands at dawn.

The most flexible heater in the average Estonian house is probably the one buried in the bathroom floor. It is small, it is always on, the owner barely thinks about it, and it will happily shift its consumption around the day if something tells it to.

Volton does the telling. Through Volton Home the optimiser talks to whichever thermostat the home has, or to a retrofit relay where the existing thermostat is too old to talk, and schedules each zone against tomorrow's prices. The homeowner keeps one comfort temperature in the app and never has to think about the rest. Floor heating is one of the loads quietly pulling its weight under the tiles.