Key takeaways
- Whole-house TRVs save 8–12% of heating costs, £60–£120 a year typically
- Basic £12 TRVs capture most of the saving; smart ones add schedules, not magic
- Screw-on head swaps are DIY; valve body changes are a small plumbing job
- Leave the room with the wall thermostat TRV-free
- Skip them if every room runs warm all day anyway
The short answer
TRVs save 8–12% of a heating bill, typically £60–£120 a year, and basic ones cost £10–£15 a radiator. A whole-house set runs £80–£150 and pays back in about two years.
Smart TRVs at £40–£60 each add per-room schedules rather than extra efficiency. Leave the room with the wall thermostat without one, and skip the lot if every room in the house runs warm all day anyway.
What a TRV actually does
A thermostatic radiator valve senses the air temperature next to the radiator and throttles the hot water flow when the room reaches the number on the dial. That is all. The boiler still decides when heat is available; the TRV decides whether this particular room takes any.
The saving comes from rooms you do not live in. Without TRVs, the spare room, hallway and utility get exactly the same heat as the living room, all day, every day the heating runs.
The numbers
| # | Setup | Cost | Annual saving | Payback | Best for |
|---|---|---|---|---|---|
| 1 | Basic TRVs, whole house (8 rads) | £80–£150 | ~£60–£120 | 1.5–2 years | Any home with unused rooms |
| 2 | Smart TRVs, whole house | £320–£500 | ~£100–£180 | 3–4 years | Schedules that differ by room |
| 3 | Smart TRVs, 2–3 key rooms only | £120–£200 | ~£60–£110 | 2–3 years | The pragmatic middle |
Field studies put whole-house TRV savings at 8 to 12% of the heating bill. On a typical £700 heating year that is £56 to £84, more in bigger houses with more unused rooms.
Basic vs smart: an honest comparison
Basic TRVs (£10–£15 each) are set-and-forget. Number 3 on the dial is roughly 20°C. They cannot follow a schedule, so the spare room is cool all the time rather than warm only when guests come.
Smart TRVs (£40–£60 each) add per-room schedules and app control: the home office warm 9 to 5, the bedrooms warm at 10pm, everything else cool. They save more in theory; in practice the gap over well-set basic TRVs is modest, and each one wants batteries every year or two. Buy smart for rooms with genuinely different schedules, basic everywhere else.
Fitting them
- Most radiators accept a TRV head with no plumbing: unscrew the old head, screw on the new. Check whether your valves are a standard M30 fitting.
- Older wheel valves need the valve body swapped, a 20-minute job per radiator for a plumber, or DIY with the system drained.
- Leave one radiator without a TRV (usually the hallway, wherever the wall thermostat lives). The boiler needs at least one open circuit, and two thermostats in one room fight each other.
When TRVs are NOT worth it
- Every room in daily use at the same temperature: nothing to throttle, little to save.
- One-radiator flats: the wall thermostat already is the room control.
- Heat pumps running very low flow temperatures: some systems are designed to run open and modulate at the unit; follow the installer's guidance rather than retro-fitting TRVs.
Frequently asked questions
What do the TRV numbers mean?
Roughly: 1 ≈ 12°C, 2 ≈ 16°C, 3 ≈ 20°C, 4 ≈ 24°C. They are targets, not valve openings. A room on 3 is being held near 20°C, setting 5 does not heat it faster, it just overshoots.
Should the TRV be on frost setting in unused rooms?
Use 1 or 2 rather than the frost symbol for rooms in the heated envelope. Fully cold rooms next to warm ones attract condensation on the shared walls. The snowflake setting is for genuinely unoccupied properties.
Do smart TRVs work with any boiler?
The valves themselves work with any wet radiator system. The clever integrations (calling for heat, working with the smart thermostat) depend on the ecosystem, mixing brands is where the frustration lives. Pick one system and stay in it.
Can I fit TRVs in a rented home?
Screw-on head swaps on existing M30 valve bodies are reversible and generally uncontroversial, but valve body changes are plumbing and need the landlord. Worth asking: it is their EPC that improves.
Sources
Energy Saving Trust typical savings data, Ofgem Q3 2026 price cap. Figures are indicative for a typical 3-bed gas-heated home in England; electric heating multiplies fuel-cost savings by about 3.5.