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Greenhouse and shed frost thermostats in the UK

Updated: October 2026

An overnight air frost can strip tender leaves and crack pots before you hear it on the morning forecast. If you heat with a tubular heater, a fan heater or an oil-filled radiator on a UK socket, a greenhouse frost thermostat can cycle that heat just enough to stay above freezing without running full daytime temperatures. This page is for greenhouses, sheds and aviaries. Combi boiler wiring needs a volt-free stat, covered on [frost stats for combi boilers](/hub/thermostats/frost-thermostat/sub/frost-thermostat-combi-boiler). Model scores sit on the [frost thermostat comparison](/hub/thermostats/frost-thermostat). If you are still choosing between a plug-in and a wired stat, use the buying guide linked below.

An overnight air frost can strip tender leaves and crack pots before you hear it on the morning forecast.

Our top picks

LOWENERGIE LOWENERGIE TH-926T

Best overall

LOWENERGIE LOWENERGIE TH-926T
8.4/10about £17.89
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XIEHUZA XIEHUZA digital plug-in

Best value

XIEHUZA XIEHUZA digital plug-in
6.8/10about £14.99
View offer
KETOTEK KETOTEK digital plug-in

Alternative

KETOTEK KETOTEK digital plug-in
4.3/10about £25.99
View offer
On this page
  1. 1.Frost-free and plant comfort
  2. 2.Plug-in stats and heater loads
  3. 3.Probe placement and calibration
  4. 4.Analogue and digital in a greenhouse
  5. 5.Overnight checklist

Frost-free and plant comfort

UK greenhouse suppliers often describe a frost-free hold around 2–7 °C, depending on the crop. Lower numbers suit hardy stock. Higher numbers suit tender plants that still need more than “not frozen”. Protecting hardy plants is not the same job as keeping seedlings at a growing temperature. A stat set near +5 °C can stop ice on the glass and keep many overwintering plants alive. Class differences are in the frost thermostat buying guide.

Plug-in stats and heater loads

Most UK gardeners pair a BS 1363 plug-in thermostat with a greenhouse heater. Our listings show 13 A, about 3 kW resistive, on the LOWENERGIE TH-926T and the KETOTEK, against 10 A on the XIEHUZA, roughly 2.3 kW at 230 V. Size the heater from the maker’s guide, not from an unsourced watts-per-square-metre rule, then check full load against the socket rating. A tubular or oil-filled heater is the straightforward resistive match. A fan heater is inductive. The LOWENERGIE lists 460 W inductive, separate from the 3 kW resistive line. Many setups leave the heater on maximum and let the stat switch the socket. Cooling mode left on in January leaves the heat off. An RS PRO plug-in at 5–25 °C and 13 A is the same class, so verify the box in front of you.
LOWENERGIE LOWENERGIE TH-926T

Testsieger

LOWENERGIE LOWENERGIE TH-926T
8.4/10about £17.89
View offer

Probe placement and calibration

If the sensor sits in the plug body, hang the controller where the air matters: about mid-height, out of direct sun, and not tight against a cold metal frame. A remote probe, 2–3 m on the digital listings here, belongs at plant height in the shade. Route the cable so sun does not bake the tip while roots freeze elsewhere. On the first cold nights, add a max/min thermometer on the bench. LOWENERGIE buyers often report the dial about 2 °C high. If the minimum was 3 °C while the dial said 5 °C, nudge down in small steps. Keep a probe out of the soil unless the listing allows immersion. The XIEHUZA mentions a waterproof probe. Do not bury it where water sits. Close vents at dusk if you rely on the overnight hold.

Analogue and digital in a greenhouse

The analogue in our set, the LOWENERGIE at about £17.89, leads on review volume: 105 amazon.co.uk reviews. It is one frost hold, the dial survives a power cut, and the socket is 13 A resistive. The trade-off is a +5 °C minimum, a possible dial offset, and a sensor in the plug. The XIEHUZA at about £14.99, with 36 reviews, adds a probe and an LCD, with a 10 A cap. That suits a modest tubular load and not a 3 kW fan on full. The KETOTEK at about £25.99 advertises day and night schedules and a 3 m probe, but the extract had no reviews. Choose it only if you will use the schedules. None of these call a boiler. They switch a socket. Fitting steps are on how to install a frost thermostat.

Overnight checklist

Before a cold night, match heater watts to the 10 A or 13 A limit, and a fan to any inductive line. Select heating mode, set the hold at or above the device minimum, often +5 °C, and put the sensor in the coldest air out of the sun. Leave a max/min thermometer for about three nights, keep the RCD sound, and avoid an underrated extension lead. Close the vents before dusk. A greenhouse plug-in will not call the boiler if the worry is house pipes.

Common questions

What temperature keeps a greenhouse frost-free?
Guides often cite roughly 2–7 °C, depending on the plants. Many plug-in stats bottom at +5 °C, which suits hardy overwintering if you check the hold with a thermometer. Tender crops may still need more than that minimum overnight.
Will a plug-in stat run a tubular heater safely?
Yes, when the resistive watts sit inside the 13 A or 10 A limit on the stat, the heater label matches, and the circuit is sound. A fan heater also has to respect any lower inductive limit printed on the controller.
Where should I put the sensor probe?
Put it at bench height, in the shade, in air that stands for the plants. Do not leave the tip in sun on the cable, tight against a cold metal frame, or buried in soil unless the listing marks the probe for that.
How much heater wattage do I need?
Size the heater to the greenhouse volume, the glazing and the vents, using the heater maker’s guidance. This page does not state an unsourced watts-per-square-metre rule. Then check that full load stays inside the stat’s 10 A or 13 A socket rating.
Can I use the stat for cooling in summer?
Many plug-ins have a cooling mode that energises the socket above the setpoint. Use it on purpose for an extract fan. Leave heating mode selected in winter, or frost heat stays off on the coldest night. Switch it back before the first frost.
Why does my stat read about 2 °C high?
Analogue plug-in reviews, including LOWENERGIE buyers, often report that offset against a separate thermometer. Run a max/min overnight and nudge the dial in small steps until the recorded minimum matches the frost hold you want. Do not trust the printed scale alone.
Is 5 °C enough for tender plants?
For a frost-free structure and hardy stock, a hold near 5 °C often is. Tender species may need higher daytime heat than a minimal frost hold provides. A plug-in that cannot be set below +5 °C cannot follow a 2 °C target from a growing guide.

Related pages

Best frost thermostat

Frost thermostat

Frost thermostat buying guide: pick the right class

Frost stats for combi boilers in lofts and garages

How to install a frost thermostat: UK loft or plug-in

Sources

Public UK sources named below. amazon.co.uk prices, stars and review counts on these five listings were read on 19 October 2026. Page updated October 2026.

  1. Crawley Borough Council — Scott Summers Court boiler user guide (PDF) (retrieved 19 October 2026)
  2. Bradfords — Drayton RTS3 frost stat (retrieved 19 October 2026)
  3. Two Wests — The A–Z of greenhouse heating (retrieved 19 October 2026)
  4. RS PRO plug-in thermostat (UK spec) (retrieved 19 October 2026)
  5. amazon.co.uk listings TOWER B07D4GNW18, LOWENERGIE B0BPJT8WQ3, KETOTEK B0GQ82T5C8, XIEHUZA B0CSG6PP7N, GLOGLOW B0CWZ7TWWQ (retrieved 19 October 2026)