Frost-free runs $10 to $120 a month. A warm growing house runs $100 to $600-plus. What size, glazing, and climate do to your winter bill.
Budget
Quick answer: Heating a backyard greenhouse runs from about $10 a month to over $600, and the target temperature drives the bill more than the size does. Keeping a small twin-wall house frost-free at 40F in a mild climate is roughly $10 to $40 a month, while holding a large single-glass house warm enough for winter tomatoes can pass $600. Single-pane glass loses about twice the heat of twin-wall polycarbonate, so glazing and insulation move the bill as much as square footage. For most buyers the honest move is to heat only to frost-free and run a heated propagation bench for seedlings, not to warm the whole structure. Verify current electricity and propane prices for your area, because an energy-cost swing changes every number here.
Best for
Buyers pricing the winter running cost before they commit, so heating never becomes a surprise line every December.
Wrong fit
Buyers who only want an unheated spring-and-summer greenhouse and will not run it through frost.
Tradeoff
A frost-free greenhouse is cheap to run and saves tender plants. A warm winter-growing house costs real money every month, and glazing decides how much.
Heating a backyard greenhouse costs somewhere between about $10 a month and over $600, and the number that moves it most is not the size, it is the temperature you hold. Frost-free protection at 40F is cheap. Growing tomatoes in January is not. A small twin-wall house kept just above freezing in a mild climate can run $10 to $40 a month, while a large single-glass house kept warm through a hard winter can pass $600. Same idea, very different bill.
We don't sell greenhouses. We save you from buying the wrong one, and heating is where a good buy quietly turns expensive. This page prices the running cost by size, glazing, and climate, and tells you when heating is worth it and when it is money down the vent. Heating is a running cost, not a one-time line, so budget it before you buy, not after. The full installed picture is in the real cost of a greenhouse.
Quick Answer: What Heating Actually Costs Per Month
These are winter monthly ranges for the coldest months, twin-wall polycarbonate glazing, electric heat at roughly $0.16 per kWh (the US average, verify at write time). Single-pane glass loses about twice the heat, so double the frost-free numbers for a glass house.
Greenhouse
Frost-free (40F), mild climate
Frost-free (40F), cold climate
Warm growing (55-60F), cold climate
Small (6x8, ~48 sq ft)
$10-40/mo
$40-120/mo
$120-300/mo
Medium (8x12, ~96 sq ft)
$25-70/mo
$80-220/mo
$250-500/mo
Large (10x16, ~160 sq ft)
$45-130/mo
$150-400/mo
$400-800+/mo
Every figure here is illustrative and worth verifying at write time against your energy rate and climate zone. The math depends on four things: your target temperature, your coldest outdoor lows, your glazing R-value, and your fuel price. Change any one and the bill moves.
Why Glazing Changes the Bill as Much as Size
A greenhouse leaks heat through its walls all winter, and how fast it leaks is set by the glazing. Single-pane glass sits around R-0.9. Twin-wall polycarbonate is about R-1.7, roughly double the insulation, so it holds heat with about half the energy. Triple-wall poly reaches R-2.5 to R-2.8 and cuts the bill further, at the cost of light. That is why a beautiful single-glass house is the most expensive one to heat, and why cold-climate buyers so often land on polycarbonate. The full glazing tradeoff, light versus insulation, is in glass vs polycarbonate.
Size matters too, but it compounds with glazing. A too-big greenhouse is expensive to heat every winter, which is the real reason "buy one size up" is good advice only up to a point. Where sizing turns against you is worked through in what size greenhouse do I need.
When Heating Is Worth It, and When It Is Not
There are three honest heating goals, and they price very differently.
Frost protection (35 to 40F). Keeps tender plants, overwintering pots, and citrus alive through the cold months. This is the cheap, sensible goal for most buyers, and a small thermostatic heater does it for tens of dollars a month, not hundreds.
Cool growing (45 to 50F). Lets you keep salad greens and hardy crops going and start seeds early. A real but manageable cost.
Warm growing (55 to 65F). Tomatoes, peppers, and tropicals through winter. This is the expensive goal, often the biggest single line on the whole greenhouse budget, and in a cold climate it can cost more per winter than the plants are worth.
The honest answer for most home gardeners is frost-free, plus a heated propagation bench or a small heated seed mat for the trays that actually need warmth. Heating a 15-degree cushion around a few trays costs a fraction of heating the whole airspace. If your dream is a warm room full of winter growth, price the warm-growing column above for your size before you commit, because that is the number that surprises people.
How to Cut the Heating Bill Before You Spend on Fuel
Insulation beats brute-force heat every time. A few moves pay for themselves in one winter:
Bubble insulation on the inside of the glazing over winter. Cheap horticultural bubble wrap can cut heat loss by 30 to 40 percent, though it costs you some light. Verify the exact figure against the product.
Heat only the zone you need. A thermostatically controlled heater and a small heated bench beat warming the full volume.
Seal the gaps and add thermal mass. Water barrels and a tight door smooth the temperature swings so the heater cycles less.
Right-size the glazing at purchase. Twin or triple-wall poly is a one-time cost that lowers every heating bill for the life of the house. This is the cold-climate buyer's biggest lever, and it is covered in best greenhouses for cold climates.
One caution that runs the other way: heating and ventilation are linked. A sealed, heated greenhouse still overheats on a sunny winter afternoon, and it still needs airflow to keep disease down. Do not seal it so tight that it cooks or turns damp. The ventilation side is in ventilation and overheating.
Budget It by Your Goal
Just want to keep plants alive through frost? Budget frost-free heating: a thermostatic electric heater and $10 to $130 a month depending on size and climate. Insulate with bubble wrap and heat a bench for seedlings. This is the right call for most buyers.
Want to grow warm crops all winter? Budget the warm-growing column, $120 to $800-plus a month in a cold climate, and choose twin or triple-wall glazing to keep it from being worse. Price it honestly before you buy, because this is the line that turns a hobby into a utility bill.
Actually want a heated room to sit, work, or read in year round? A greenhouse is built to grow plants, not to be a comfortable four-season room, and heating one to living-room temperature all winter is expensive and still drafty. That is an office pod, and it is a different structure with real insulation. Weigh it at backyardoffice.guide before you spend greenhouse money heating glass.
Whatever your goal, the running cost is part of the real price of the greenhouse, not an afterthought. Price the winter before you fall for the catalog photo.
Frequently Asked Questions
How much does it cost to heat a greenhouse in winter?
For a twin-wall house kept frost-free at 40F, roughly $10 to $40 a month in a mild climate and $40 to $120 in a cold one. Push it up to warm-growing temperatures, 55 to 60F, and a cold-climate bill can run $250 to $800-plus a month depending on size. A single-glass house costs about double a twin-wall one to hold the same temperature. Verify against your own energy rate, because fuel price drives the whole number.
Is it cheaper to heat a glass or a polycarbonate greenhouse?
Polycarbonate, clearly, and it is not close. Single-pane glass sits around R-0.9 while twin-wall poly is about R-1.7, so the glass house loses roughly twice the heat and costs about twice as much to keep warm all winter. Glass buys you light clarity and looks, not a cheap heating bill. If low running cost matters more than a clear view, twin or triple-wall poly is the honest choice.
Do I really need to heat my greenhouse at all?
Only if you want to grow or protect plants through frost. Plenty of gardeners run an unheated greenhouse for spring seed-starting and a longer autumn and never turn on a heater, and that is a valid, cheap way to use one. You need heat once you want to overwinter tender plants or grow through the cold months. If you never plan to run it below freezing, skip the heating budget entirely.
What is the cheapest way to keep a greenhouse from freezing?
Insulate first, then heat the smallest zone you can. Line the inside with horticultural bubble wrap for the winter, which can cut heat loss by 30 to 40 percent, seal the door and gaps, and add water barrels for thermal mass. Then run a thermostatic electric heater set to 40F so it only fires when needed, and use a heated bench for seedlings instead of warming the whole airspace. That combination keeps a small greenhouse frost-free for tens of dollars a month, not hundreds.
Is a heated greenhouse worth it, or should I just buy a bigger one to heat less?
Bigger is the wrong direction if heating cost is your worry, because a larger greenhouse costs more to heat, not less. The question is your goal: frost-free protection is cheap and worth it for most people, while warm winter growing is a real monthly cost you should price before you buy. Buy the size that fits how you garden, insulate it well, and heat only what you need. The sizing tradeoff is in what size greenhouse do I need.
Will heating my greenhouse make my electric bill jump?
It can, especially with an electric heater in a cold climate at warm-growing temperatures, which is why the running cost belongs in your budget before you buy. Frost-free heating in a well-insulated twin-wall house is modest, often less than a space heater in a spare room. Warm-growing a large glass house is where the bill climbs into hundreds of dollars a month. Price the warm-growing column for your size and climate, and if the number stings, drop to frost-free or better glazing.
Methodology
These guides are built from manufacturer documentation, public specifications, primary research where health claims matter, and repeated buyer questions that show up in real ownership and installation decisions.
Manufacturer responses can clarify pricing bands, warranty terms, support footprint, or common mistakes. They do not move a page up the shortlist on their own.
