The main cost factors
- 1
Floor area
More floor means more pipe, more insulation and more time, though the fixed elements such as the manifold and controls are spread across a larger area.
- 2
New floor or retrofit
Laying pipes into a new screed in an extension is the most straightforward route. Retrofitting into an existing room depends on what the floor is made of and how much height you can afford to lose.
- 3
Floor build-up
Screeded systems, low-profile overlay boards and pipes between joists with spreader plates all involve different materials and labour. The finished floor height, door thresholds and kitchen plinths all need to work.
- 4
Manifold and pump
Every system needs a manifold to distribute water to each circuit. Where it shares a boiler with radiators, a mixing valve and pump are usually needed to deliver the lower temperature the floor runs at.
- 5
Zones and controls
Each zone has its own thermostat and actuator. More zones give more control but add equipment and wiring.
- 6
Boiler compatibility
Your boiler needs the capacity to serve the extra heating and a sensible connection point. If the boiler is due for replacement, combining the jobs can affect the overall scope.
Retrofit: where the hidden work is
On a solid floor, a retrofit usually means either lifting the existing finish and screed, or laying a low-profile system on top. Low-profile retrofit systems only add around 15–20mm to floor height, but that still affects doors, thresholds into other rooms and fitted units. On suspended timber floors, access from below or lifting boards is needed.
Insulation beneath the pipes matters. Without it, a good share of the heat goes down into the ground or the void rather than up into the room, which affects both comfort and running costs.
Running-cost principles
Underfloor heating runs at lower water temperatures than radiators because it heats a much larger surface. A condensing boiler operates more efficiently when the water returning to it is cooler, so a well-designed floor system can help the boiler work in its efficient range.
Floors take longer to warm up and cool down than radiators, so they suit steady schedules rather than short bursts. The floor covering matters: tile and stone pass heat readily, while thick carpet and underlay hold it back. Good insulation beneath the pipes and in the room itself has the biggest single effect on what the system costs to run.
What a clear quote should show
- The floor area and number of circuits
- The floor build-up proposed and any change in floor height
- Manifold position, mixing arrangement and pump
- Number of zones and the thermostats included
- How the system connects to the boiler and existing radiators
- Pressure testing and commissioning
Decide early. Underfloor heating is at its most straightforward when it is part of the plan for the floor, not an afterthought once the finish is chosen.