Greenhouse, Grow Tent and Grow Room Heaters: Which to Choose

A grow tent, grow room or greenhouse that gets too cold at night slows plants down, and the usual fix is a small electric heater on a thermostat. This guide gives the temperatures to aim for, compares the heaters we sell and shows how to control them. It covers electric heating only.

What temperature to aim for

Our airflow, temperature and humidity guide gives 22-26°C for vegetative growth and 20-25°C for flowering, and says too cold slows growth and reduces nutrient uptake.

Indoors, the light warms the tent while it is on, so a heater is mostly a lights-off job (see grow room running costs). The temperature drop at lights-off pushes humidity up, because cool air holds less water (see grow tent humidity). A greenhouse usually has no grow light to help, so decide first whether you want frost kept out or plants kept growing: the second takes far more heat.

Measure before you buy: hang a hygrometer at plant height and note the overnight low for a few nights. The ThermoPro TP358 records the 24-hour high and low and has a programmable low-temperature alarm; the budget Digital Hygrometer has a max/min memory.

Tube heater, fan heater or smart heater?

Tube heaters give gentle background heat from a slim tube along a wall or under a bench. The Hylite Tube Heaters and Gorilla Tube Heaters pages both say they help reduce condensation and mould (see powdery mildew). Neither page lists a thermostat.

Fan and space heaters warm a whole space quickly; their pages list a thermostat. The Gorilla 2kW Heater page says it can heat a space of about 40 cubic metres, and warns not to point it at the plants, which can dry them out, and to leave plenty of space around it.

A smart heater reads the air itself: the AC Infinity Thermoforge T7 VPD Heater page says it adjusts its heat output to keep temperature and humidity stable for a balanced VPD, sends alerts to an app and works with the AC Infinity AI+ Controller and Cloudline Pro EC Fans. The Thermoforge we sell is the T7.

The heaters we sell, as their product pages describe them.
Heater	Output	Control and safety	Where its page puts it
Hylite Tube Heaters	28, 55, 90, 120 or 190 W; 300-1500 mm long	Overheat protection; IP55 splash-proof	Grow rooms, greenhouses, propagation areas
Gorilla Tube Heaters	60, 120, 180 or 240 W; 300-1200 mm long	Thermal cut-off	Grow rooms, tents, propagation areas
GroWarm 2kW Fan Heater	2 kW, three modes	Thermostat, its page says; overheat cut-off; IP24	Small to medium-sized spaces
Gorilla 2kW Heater	2 kW, adjustable settings	Basic thermostat; thermal cut-out	A space, not pointed at plants
AC Infinity Thermoforge T7 VPD Heater	1000 W element	Own sensors and app; tip-over and overheat shut-off	Grow tents, larger indoor set-ups

Which heater for which space?

Our advice, not a maker's:

One tent in a heated house: you may not need a heater at all; if you do, a tube heater for the lights-off hours. Our running costs guide uses a 60 W Gorilla tube for a 1 m tent. Fit it low, since warm air rises, with a clip fan moving the air.
Tents in a cold garage or loft: a tube heater in each tent, on a thermostat - heat the tent, not the room, as our running costs guide says. The extractor swaps tent air for room air, so if the tubes fall short, warm the room too.
A grow room: a 2 kW heater, kept out of any tent: even a 240 x 240 x 200 cm tent is only 11.5 cubic metres (see our fan and filter guide), far less than the space the Gorilla 2kW page gives.
A greenhouse: tube heaters along the wall or under the staging, on a thermostat. Of the tube heaters, only the Hylite page gives a splash rating (IP55), and it says its aluminium body withstands humid greenhouse conditions.
An automated tent: the Thermoforge T7, with the AI+ Controller.

Start small, on a thermostat, and go up a size only if the overnight low falls short.

Thermostats and fan controllers

For the tube heaters, use the temperature model of the G.A.S Day & Night Controllers: its page lists that one for heaters, names greenhouses and says settings change with the light cycle.

The extractor pulls warm air out, so a fan controller that reads temperature slows it when the tent is cold instead of fighting the heater: the SMSCOM Smart Controller 6.5A (probe included), the Rhino 1EC Fan Controller (one Rhino EC fan; other makes may need an adapter), the G.A.S AC-EC Controller (AC or EC fans) or the G.A.S. Enviro4 EC Fan Controller (more than one EC fan).

Our advice: keep some extraction in the dark period, when humidity is usually highest, so the G.A.S AC-EC and Enviro4, which also act on humidity, are the better choice. Fit Back-draft Shutters (100 to 315 mm) on the extraction ducting: their page says they close when the fan is off, stopping cold air coming in. In a loft, insulate the ducting too (see what size grow tent).

Heating the nutrient tank and young plants

Cold nutrient solution slows roots too: the Hailea Water Chillers page says keeping it at 18-21°C improves nutrient uptake. In hydroponics, our flood and drain guide says to use one of the Eheim Tank Heaters in a cold room: fully submersible and shatter-proof, with their own temperature control and safety shut-off, the page says.

Eheim Tank Heaters, by the tank sizes on the product page.
Eheim heater	For a tank of
25 W	20-25 litres
50 W	25-60 litres
75 W	60-100 litres
100 W	100-150 litres
125 W	150-200 litres
150 W	200-300 litres

Check the temperature with a meter that reads it, such as the Aqua Master Combo Pen P110 Pro.

For seeds and cuttings, a heated propagator such as the Garland XL High Dome Heated Propagator warms the compost rather than the room: see sowing seeds indoors and propagators and cuttings.

Using a heater safely

Clear space, dry plugs. Keep tent walls, pots and leaves clear of any heater, a tube heater included, and plugs off the floor with a drip loop (see our grow tent setup guide). In a greenhouse, have an electrician fit the supply.
Add up the watts. A 2 kW heater is a big load: give it a wall socket of its own where you can, and keep within the rating of each socket and extension lead.

Quick answers

What is the best heater for a grow tent?

Our advice: a tube heater on a thermostat, for the lights-off hours. For a tent you want automated, the Thermoforge T7 has its own sensors and app, its page says.

What temperature should a grow room be?

22-26°C in vegetative growth and 20-25°C in flowering, our airflow guide says. Growers commonly let the dark period run a little cooler; the heater's job is to stop the overnight low falling well below these. Check it at plant height.

What is the best greenhouse heater?

Our advice: tube heaters along the wall or under the staging, on a thermostat. The Hylite page names greenhouses and gives IP55 (splash-proof).

Does a tube heater need a thermostat?

Yes, in our view. Neither tube heater page lists one, so it runs whenever it is switched on, mild nights included. Control it with the temperature model of the G.A.S Day & Night Controllers.

More Growers' Guides

Not sure what you need? Call the shop on 0117 971 3000 or pop in to the Bristol store and we'll help you pick.