Radiant Floor Heating Explained
Updated 2026-08-16 · 8 min read
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Two systems share the name radiant floor heating, and they're not variations on a theme — they're different products for different jobs.
Hydronic circulates warm water through tubing in the floor. It's a whole-house heating system, expensive to install, and its running cost depends on whatever heats the water.
Electric runs resistance cable or mats under the floor covering. It's cheap to install, expensive to run, and it's normally used to warm one room.
Confusing the two is the source of most bad decisions in this area.
How does radiant heat work?
Both types warm the floor surface, which then heats the room in two ways: by radiant transfer to people and objects in the space, and by convection as air contacts the warm floor.
The comfort argument is real. Radiant systems warm surfaces and bodies directly rather than blowing warm air around, which produces:
- Even temperatures with no hot ceiling and cold floor stratification
- No drafts and no blown dust
- Comfort at a slightly lower air temperature, because warm surfaces make you feel warmer than the thermostat reading suggests
- Silent operation
The trade-off is thermal mass and response time. A concrete slab with tubing in it takes hours to warm up and hours to cool down. That's fine for steady heating and poor for quick setbacks — which changes how you control it.
Hydronic radiant
Warm water circulated through PEX tubing by a pump, fed by a heat source, distributed through a manifold with a loop per zone.
Installation methods:
| Method | Where | Notes |
|---|---|---|
| In-slab | New construction, basements | Tubing tied into the slab reinforcement. Best performance, highest thermal mass |
| Thin slab / gypsum overpour | Over an existing subfloor | Adds height and weight; check structure |
| Above-floor panels | Retrofit | Grooved panels with heat transfer plates; less height and mass |
| Staple-up / below-floor | Retrofit from below | Tubing under the subfloor with transfer plates. Lowest output, needs higher water temperature |
Heat sources: a boiler (gas, propane, oil, electric) or a heat pump. This is the important part economically — the floor is just a distribution method, and what heats the water determines the running cost.
Why heat pumps and radiant floors pair well: floor loops run at relatively low water temperatures, and heat pumps are more efficient producing lower-temperature water than high-temperature water. An air-to-water heat pump feeding radiant floors is an efficient combination. See geothermal vs air source heat pump and electrifying a home with radiators for the related retrofit question.
Costs: high. Tubing, manifolds, pumps, controls, a heat source, and floor assembly work. It makes economic sense in new construction or a gut renovation where the floor is open anyway. Retrofitting into a finished house is rarely worth it.
No cooling. Radiant floors heat only. You need a separate cooling system, which is a real cost to factor in — see central AC vs mini split.
Electric radiant
Resistance cable or pre-spaced mats installed under the floor covering, usually in the thinset under tile, controlled by a floor-sensing thermostat.
Where it fits: bathrooms, kitchens, entryways, small additions — rooms where a warm floor is a comfort upgrade rather than the primary heat source.
Why it's not whole-house heat: it's resistance heating, COP 1.0, exactly like electric baseboards. Every unit of electricity produces one unit of heat, and heating a whole house that way is expensive. See heat pump vs electric resistance heat and electric baseboard heating explained.
Electrical requirements:
- Sized in watts per square foot of heated area, typically in the range of 10–15 W/sq ft depending on the product
- Needs a dedicated circuit sized for the connected load, treated as a continuous load per the NEC
- GFCI protection is required for electric floor heating — it's in a wet-adjacent location and the code requires it
- The thermostat is line voltage with a floor sensor, not a standard low-voltage thermostat
- Permit and inspection apply
Check the load against your panel with the home electrical load calculator and conductor sizing against the wire and breaker size reference. If capacity is tight, see Electrical panel upgrade.
Install notes: the sensor probe must be positioned between cable runs, not on top of one, and it should be run in a conduit sleeve so it can be replaced without lifting the floor. Test the cable's resistance before, during and after installation — a cable damaged during tiling is nearly impossible to repair afterwards. Never cut or shorten a heating cable.
Floor coverings
This constrains the whole decision, so check it early.
| Covering | Suitability |
|---|---|
| Tile and stone | Ideal — conduct well, tolerate the temperature, high thermal mass |
| Engineered wood | Usually fine within the manufacturer's temperature limit |
| Luxury vinyl | Often suitable; check the product's rating |
| Solid hardwood | Risky — can cup or gap with heat cycling; some species and installations are unsuitable |
| Laminate | Depends on the product; many are rated, some aren't |
| Carpet | Insulates the floor and reduces output. Thick carpet plus thick underlay can defeat the system |
Always check both manufacturers — the flooring's maximum surface temperature and the heating system's requirements. A floor covering that voids its own warranty over radiant heat is an expensive mistake.
Controls
Radiant floors are controlled differently from forced air, because of the thermal lag.
- Floor sensors, not just air sensors. Most systems use a floor temperature probe, often with a maximum floor temperature limit to protect the covering.
- Deep setbacks don't work well. A slab that takes hours to respond can't recover quickly from a large setback, so the saving you'd expect from a night setback often doesn't materialise. Steady operation with modest adjustment usually performs better.
- Zoning is straightforward on hydronic — a loop and a valve per zone.
- Outdoor reset on hydronic systems varies water temperature with outdoor conditions, improving both comfort and efficiency.
Running cost
The system type tells you nothing on its own. The heat source determines the cost.
- Electric radiant: kWh = watts ÷ 1,000 × hours, times your rate. Same arithmetic as any resistance heat. Work it out with the electricity cost calculator.
- Hydronic from a gas boiler: whatever your gas costs, divided by boiler efficiency.
- Hydronic from a heat pump: electricity divided by the COP — potentially the cheapest of the three.
Compare per unit of delivered heat in heating cost by fuel type.
And insulate under it. Radiant heat goes in every direction, including down. A slab without adequate under-slab and edge insulation loses a meaningful share of its output into the ground. This is not optional — it's the difference between an efficient system and a very expensive one.
Hydronic or electric radiant floor — which should you choose?
Electric mat when: you want a warm bathroom or kitchen floor, you're retiling anyway, and it's supplemental comfort rather than primary heat.
Hydronic when: it's new construction or a gut renovation, you're heating the whole house, and you're pairing it with an efficient heat source — ideally a heat pump.
Neither when: you're retrofitting whole-house heating into a finished home. A ducted or ductless heat pump costs far less, provides cooling too, and doesn't require lifting every floor. See ductless vs central heat pump.
The bottom line
Hydronic and electric radiant are different products. Hydronic is whole-house heat, expensive to install, efficient when fed by a heat pump, and only economical when the floor is already open. Electric is a room-scale comfort product — cheap to install, resistance-priced to run, and a poor choice as primary heat. Check floor covering compatibility before anything else, insulate under the assembly, and don't expect deep setbacks to save money on a high-mass floor.
Compare whole-house options with the heat pump payback calculator.
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