Before comparing specific models, it helps to know what you're solving for. A heater that's oversized for your greenhouse wastes energy and can create uneven hot spots near plants, while one that's undersized won't keep up during a hard freeze. Your available power source matters just as much. After all, a heater that needs electricity does you no good if the greenhouse sits far from an outlet, and a fuel-burning heater needs proper ventilation regardless of size.
Electric Greenhouse Heater Basics
This is the simplest option when reliable power is already running to the structure. These units pair well with thermostatic controls, cycling on as temperatures drop and easing off once the target is reached, so you don't have to manually adjust anything throughout the night. Additionally, capacity should be matched to your greenhouse's dimensions, insulation, and expected outdoor lows, along with the temperature range your specific plants need, not just whichever model has the highest wattage on the shelf.
Propane Greenhouse Heater Overview
This is the better fit when your greenhouse doesn't have convenient electrical access, or when you need more heat output than a typical electric unit provides. Because propane units don't rely on an outlet for their primary heat source, they also make a reliable backup during a power outage. Ventilation and clearance matter even more here. Always follow the manufacturer's requirements for fuel connections, clearance from combustible materials, and airflow, and check connections regularly throughout the season.
A Closer Look At The HeatStar Blue Flame Heater
For smaller greenhouses, the HeatStar Blue Flame Heater (10,000 BTU Propane) is built specifically for spaces up to 300 square feet. It runs on propane, requires no chimney or venting, and includes a built-in thermostat, blower fan, and battery-powered electronic ignition, so it continues to produce heat even during a power outage. In addition, a built-in low-oxygen shut-off (ODS) sensor automatically shuts off the heater if oxygen levels drop below a safe threshold, which is important in an enclosed space like a greenhouse. Better yet, it's CSA certified for use in the U.S. and backed by a 5-year limited warranty.
Before You Order: Installation Kit And Shipping Restrictions
Before ordering, here are two things to plan for. First, this heater requires the Remote Propane Vent-Free Installation Kit to operate properly. It's sold separately or bundled at checkout, so don't purchase the heater alone expecting it to be ready to install. It also cannot currently ship to California due to state regulations on vent-free propane heaters, so we encourage California-based customers to reach out to us to discuss alternative heating options.
Choosing Between The 10K And 20K BTU Models
HeatStar's Blue Flame line comes in two sizes: the 10,000 BTU model covers up to 300 square feet and is freestanding only, while the 20,000 BTU model covers up to 700 square feet and can be either wall-mounted or freestanding. If your greenhouse is under 300 square feet, the 10K model is the right call. After all, stepping up to the 20K in a smaller space means paying for capacity you won't use. Regardless of which one you pick, both sizes require the same installation kit and share the same California shipping restriction.
Automating Your Heater With A Programmable Thermostat
Manually adjusting a heater throughout the day and night is easy to forget and hard to get right. A Programmable Outlet Thermostat for Greenhouse Heaters & Heating Mats plugs into any standard 120V outlet and automatically controls a connected appliance (e.g., a heater, seed heating mat, fan, or air conditioner), turning it on and off to hold your target temperature.
The 5-2 day programming feature lets you set one schedule for weekdays and a different one for weekends, handy if your greenhouse routine on Saturday looks nothing like your Monday schedule. It also displays both the preset and current temperature simultaneously, so you can check conditions at a glance without guessing whether the heater is doing its job.
Greenhouse Heater Sizing, Placement, And Safety
Once you've settled on a heater, sizing starts with your greenhouse's square footage and the gap between your desired indoor temperature and expected outdoor lows. Placement affects performance just as much: position the heater according to the manufacturer's instructions, avoid aiming direct heat at plants or polycarbonate panels, and use a fan to help distribute warm air evenly rather than letting it pool near the heater.
From there, safety comes down to using equipment rated for the environment and following the manufacturer's instructions without shortcuts. Check heaters, cords, thermostats, and fuel connections regularly, and make sure any electrical equipment used near the greenhouse is rated for the moisture levels a growing space can produce.
