Retrofit underfloor heating has a reputation for being disruptive, expensive or incompatible with older homes. In most Kent properties, none of that is still true. Modern overlay systems add just 16mm of build-up, sit straight on top of an existing concrete slab or floorboards, and leave you with a floor that's ready for tile, LVT, engineered wood, laminate or carpet. This guide walks through what's actually involved, what it costs, and what to look out for before you commit.
Why Retrofit UFH Makes Sense
Radiators work, but they heat the air in a room from one corner. Underfloor heating spreads warmth evenly across the whole floor surface, runs at a much lower flow temperature, and pairs particularly well with air source heat pumps. In a home that already has a condensing boiler, the efficiency gains are meaningful on a cold day. In a home moving to a heat pump, UFH is close to a requirement to get the most out of the new system.
- Even warmth: No cold corners, no hot spots next to radiators. The floor is the radiator.
- Free walls: Radiators off the wall gives you the layout freedom that bathrooms, kitchens and living rooms benefit from.
- Lower running temperatures: 35–45°C flow vs 60–75°C for radiators. Better for condensing boilers, essential for heat pumps.
- Quiet, invisible: Nothing to look at, nothing to clean around, nothing making a noise when the circulator starts.
Understanding the 16mm Build-up
The question everyone asks first is "how high will the floor go up?". With a modern overlay system the honest answer is: 16mm for the pre-grooved board, plus 4–8mm for the tile backer or smoothing compound that caps the system, plus the thickness of your chosen floor finish. Total build-up is typically 22–30mm including the finish, and almost always within the tolerance of internal doors that can be trimmed a little.
That matters. The old objection, "I'd have to rip the floor up", simply doesn't apply to a retrofit overlay. The existing floor stays where it is. We build on top of it.
Floor Finish Options
Not every finish is equally suited to UFH. Here's the honest breakdown.
- Tile and stone: The best match. Conducts heat beautifully, zero risk from movement if bedded on the right substrate. Our default finish for kitchens and bathrooms.
- LVT and vinyl: Excellent modern match. Thin, conducts well, stable under the temperature swings of UFH. Check the manufacturer's max floor-surface temperature (usually 27°C).
- Engineered wood: Good match if the board is suitable (most modern engineered boards are). Solid wood is less reliable, some boards move as the floor cycles.
- Laminate: Fine if UFH-rated. Most laminates these days are. Check the TOG value of the underlay, thick underlays act as insulation against your heating.
- Carpet: Works, but needs a low-TOG carpet and underlay combination. Thick pile and chunky underlay block the heat.
Planning a retrofit UFH project?
Call Kent Underfloor Heating on 07452 995369 for a free, no-obligation quote. We cover Sevenoaks, Bromley, Royal Tunbridge Wells and the rest of Kent.
Call for a Free QuoteWhat a Retrofit Install Actually Involves
A typical domestic retrofit install for a kitchen or living room looks roughly like this.
- Survey: We check the sub-base for level, confirm the build-up under your existing floor covering, look at how the room is heated today, and work out where the manifold and flow runs should go. This is where the quote comes from.
- Prep: On the day, we lift the existing floor covering if there is one, clean the sub-base, and prime it ready for the overlay boards.
- Boards down: Pre-grooved overlay boards are bedded onto the primed sub-base to the layout we've designed, with the grooves oriented to route the pipe efficiently.
- Pipe and manifold: 16mm PE-RT pipe clips into the grooves and feeds back to a new or existing manifold. We pressure-test the loop before anything goes on top.
- Cap layer: A tile backer, self-levelling compound or cement board caps the pipe. The finish is now ready for your floor covering.
Most domestic rooms finish in a few days. A whole-ground-floor retrofit takes a week or two depending on the layout.
Typical Costs
- Subfloor prep and coverage: £25–£45 per square metre. Covers the overlay boards, smoothing compound, and labour.
- Pipe and manifold install: Priced per job once we've seen the layout. Depends on area size, number of zones, and manifold location.
- New manifold and controls: £600–£1,200 depending on number of zones and wiring requirements.
- Typical whole-room retrofit (kitchen, ~15m²): £1,800–£2,800 all-in, including prep, pipe, manifold, pressure-test and handover.
Frequently Asked Questions
In most cases yes, with a small trim off the bottom of the door to account for 20–30mm extra build-up. We flag any doors at the survey so you know what's coming.
Yes, single rooms are a common retrofit scope. We fit the loop back to a new zone on the manifold (or a single-room manifold) and control it independently from the rest of the heating.
An overlay system responds faster than an in-screed floor because there's less mass to warm up. Typical response time is 45–90 minutes from cold to comfortable.
Usually no. Modern condensing boilers run UFH loops happily. If you're planning a heat pump upgrade, that's the right moment to design the UFH loads in.
Yes, UFH and radiators can coexist on the same heating system with a mixing valve at the manifold. Many retrofits leave radiators in the bedrooms and put UFH in the ground-floor rooms.
We smooth it with a self-levelling compound before the overlay boards go down. That's included in the subfloor-prep pricing above.
