Greenhouse Heating Options

How warm does your greenhouse actually need to be?

Start with the plants, not the equipment. A cold greenhouse that only stays a few degrees above the outside air will carry hardy greens and overwinter tough perennials. A greenhouse held above freezing protects tender seedlings and cuttings. Starting warm-season transplants early asks for more heat, and tropical or citrus plants ask for the most. Write down the lowest night temperature each plant group can tolerate, then pick the least demanding target that still fits your plan.

Your target sets your fuel bill and your risk. Every extra degree you hold against a cold night costs energy, and the cost climbs quickly as the outside temperature drops. Many hobby growers do better by matching the crop to a modest target than by chasing a warm greenhouse all winter.

What heating options can a hobby greenhouse use?

Options fall into passive and active groups. Passive heat comes from the sun and from materials that store it, so it costs little to run but cannot rescue you on a long cold snap. Active heat comes from a heater that burns fuel or draws electricity, and it holds a set temperature when a thermostat is working. Most small setups combine one passive method with one active backup.

• Passive: water barrels or masonry that soak up daytime sun and release it at night.
• Passive: an in-ground or semi-buried structure and a well-sealed north wall.
• Electric: small fan heaters or radiant units on a thermostat, powered through a properly installed outdoor-rated circuit.
• Fuel-burning: propane or natural gas units designed and listed for greenhouse use, with correct venting.
• Biomass or wood heat: possible, but needs a proper flue, clearances and attention to local fire rules.

How do you reduce heat loss before buying a heater?

Insulation and sealing usually give the best return on effort. Walk the greenhouse on a windy day and feel for drafts at doors, vents, panel joints and the base where the wall meets the ground. Seal those gaps first. A second layer of glazing film with an air gap, bubble-style insulation on the north side, and an insulated base wall all reduce the load the heater must carry.

Think about nights, because that is when you pay. Thermal curtains or a movable layer over the plants can hold warmth close to the crop. Heating the root zone with a mat under benches lets you keep the air cooler while seedlings still germinate and root well, which often costs less than warming the whole volume of air.

Which safety checks matter most with greenhouse heaters?

Greenhouses are humid, dusty and full of plants, and that mix is hard on equipment. Any fuel-burning heater needs fresh air for combustion and a way to vent exhaust outside, because combustion gases can harm people and plants. Place a carbon monoxide alarm where you can hear it if you ever enter the structure or sleep in a nearby building.

Electrical work is where hobbyists most often cut corners. Use equipment rated for damp locations, keep cords out of water and foot traffic, and have a licensed electrician install permanent circuits where required. Gas lines, tanks and venting also call for a qualified installer. Keep flammable materials, plastic film and dry plant debris well clear of any heat source, and check every heater before the first cold night, not during it.

What if the power or fuel fails on a cold night?

Plan for failure, because the coldest night often arrives with a storm. Decide in advance what you will move indoors, what you will cover, and what you will accept losing. A simple low-temperature alarm that sends you an alert is worth having if your greenhouse is out of sight of the house.

Keep a backup method that does not depend on the main one: a second heater on a different fuel, insulating blankets, or stored water mass. Test the backup in the shoulder season so you know it works.

How do you budget for greenhouse heat?

Think in cost categories instead of one purchase price. There is the heater itself, a thermostat or controller, installation by a licensed pro where needed, the ongoing fuel or electricity, insulation materials, and the monitoring and safety gear. Ask your utility about the rate structure and any outbuilding service charges, and ask your fuel supplier how tank rental or delivery works.

Before you commit, compare what you would gain with what you would spend. If the crop you want to protect is inexpensive to buy, a cold greenhouse and a good row of hardy greens may be the more sensible choice.

Last reviewed: November 12, 2026. Written by the Homestead & Small Farm Editorial Team. See our editorial policy.