Seedling heat mat: what to check before you buy

Updated: October 2026

A February windowsill in Britain often sits below the temperature on a tomato or pepper packet. A seedling heat mat is the flat pad under the tray so the compost, rather than the whole room, picks up that warmth. You are choosing among 12 amazon.co.uk listings, with shelf prices on 16 October 2026 from £8.90 to £42.99. Check the crop, then whether you can set a temperature, then the heated rectangle, then the plug and the water claim. The seedling heat mats comparison holds the full table. This page is that decision order. A purchase through our amazon.co.uk links can earn a commission at no extra cost to you.

Our top picks

Badge	Product	Control	Heated area	Supply	Note	Price	Offer
Best overall	HBN HBN 17.5 W fixed heat mat	None; leave it on until you unplug it	25 × 50 cm	230–240 V	7.8	about £14.99	View offer
Alternative	Senua Senua 20 W fixed heat mat	None; plug in only	25 × 52.7 cm	Not stated	7.0	about £14.99	View offer
	WADEO WADEO 50 W probe heat mat	Digital thermostat with a separate probe	52 × 25 cm	Not stated	8.0	about £24.22	View offer

Best overall

HBN HBN 17.5 W fixed heat mat

7.8/10about £14.99

View offer

Alternative

Senua Senua 20 W fixed heat mat

7.0/10about £14.99

View offer

Rank 3

WADEO WADEO 50 W probe heat mat

8.0/10about £24.22

View offer

On this page

1.What the mat is for
2.Control before watts
3.The heated rectangle, not the wattage
4.Plug, voltage and water

What the mat is for

Bottom heat is for germination. The Royal Horticultural Society says most seed wants about 18°C, and the packet wins when it prints a different figure. Chillies sit near 21°C, sweet peppers near 18–21°C, and aubergines at least 21°C. Lettuce and peas germinate in cooler compost, and a hot pad is a usual way to get a poor stand. The sowing window for the warm crops is on the heat mat for tomato and pepper seeds page. The mat’s job ends when the seedlings are up.

Control before watts

A fixed mat adds a lift above the room. The English Garden describes an unregulated 17.5 W mat at about 8°C above the room. That is their example, not a measurement of the HBN, and not a dial. In a 12°C porch that lift still leaves a chilli packet short. The fixed pads here are the HBN CP-C93 at 17.5 W and 230–240 V, the Senua at 20 W, and the RC SLL 18 W mats. Thermostat kits are the AOOWU sizes, the WADEO models, the HBN combo and the HYDGOOHO. The Gsycle uses three gears and has no probe. The WADEO timer is on the seedling heat mat with thermostat page.

Testsieger

HBN HBN 17.5 W fixed heat mat

7.8/10about £14.99

View offer

The heated rectangle, not the wattage

Listings here call about 25 × 51–53 cm a standard tray. That rectangle is a US 10 × 20 inch flat. A British full tray from Thompson & Morgan is 36 × 22 × 6 cm. A 25 × 52 cm mat warms one of those trays with overhang on the long side, and it will not heat two of them edge to edge. The wide options are the AOOWU title at 52 × 52 cm and the WADEO two-mat title, which prints 104 × 50 cm in the title and 52 × 25 × 1 cm on the dimensions line. The Gsycle title says 22.1 × 15.7 cm and the technical line says 1 × 0.99 × 1 cm. The HBN thermostat combo prints no heated area.

Plug, voltage and water

Where a wattage is printed, these mains mats are 17.5–50 W. Only the fixed HBN states 230–240 V, and only the HYDGOOHO states 220–240 V at 50 Hz. Under the Electrical Equipment (Safety) Regulations 2016, regulation 35, a domestic appliance for a BS 1363 socket needs a correctly fitted standard plug, or a non-UK plug with a conversion plug and a BS 1362 fuse. A code ending in EU or UK does not settle the pins. You look at the photo. IPX4 on the AOOWU pages is splashing under BS EN 60529. IP67 on the Senua and the HYDGOOHO is a temporary immersion test, not a sink wash. Who each listing is for sits on the best seedling heat mat page.

Common questions

Does a 25 × 52 cm mat fit two British full trays?

It covers one Thompson & Morgan full tray of 36 × 22 × 6 cm, with spare mat on the long side, and it does not cover two of those trays edge to edge. The 25 cm width is the limit. Senua reviews describe a 25 × 52.7 cm pad in the same way: larger than one standard tray, short of two, cooler at the edge. Two heated British trays means two mats, or a square titled 52 × 52 cm, if the box matches that title.

Which listings print a mains voltage?

The fixed HBN CP-C93 prints 230–240 V. The HYDGOOHO BHD-100 prints 220–240 V at 50 Hz. The other ten listings leave voltage unstated, including the 50 W WADEO and the Senua 20 W mat. A blank line is not 230 V. The Gsycle is the further case: reviews describe USB power, and the page prints no voltage.

Why does a model code ending in EU or UK fail to settle the plug?

HG0281EU and MS-HG0429UK are part numbers on WADEO listings. The EU code also sits next to a German language field. Neither page names the plug. Regulation 35 is about the plug fitted for a BS 1363 socket, not about the letters at the end of a code. Open the gallery. If the pins are not the UK three-pin pattern, you are into a conversion plug and a BS 1362 fuse, which is a buying decision, not a footnote.

Can you wash a mat that says IP67, IPX4 or waterproof?

IPX4 is a splash test. IP67, in BS EN 60529, includes a temporary immersion test. The AOOWU pages print IPX4 and tell you not to immerse the mat. The Senua and HYDGOOHO claim IP67 and still give you no instruction to wash the pad in the sink. Other mats only say waterproof. Wipe a spill, keep the controller dry, and leave the pad out of the basin.

What does a nameplate watt cost per day, and what does that miss?

About 11p, 13p, 19p and 32p a day, at 17.5 W, 20 W, 30 W and 50 W, is the Ofgem Direct Debit average of 26.32p/kWh from 1 October to 31 December 2026, times the nameplate, for England, Scotland and Wales. Electricity in that cap is at 0% VAT. Northern Ireland is outside it. The figure is not your meter, and a cycling thermostat should cost less.

How to use a seedling heat mat