Greenhouse Heating Costs: How to Estimate Your Winter Energy Bill

Why Greenhouse Heating Costs Are Hard to Predict

Greenhouse operators are often surprised by their first winter energy bill. A greenhouse does not just lose heat through its glazing — it also loses heat through infiltration, gains solar heat during the day, stores heat in thermal mass, and can be dramatically affected by wind. The real bill combines all of these factors in ways that vary by day, week, and season.

The good news: you can get a solid planning estimate by focusing on the most controllable and predictable factor — conductive heat loss through your glazing. This accounts for roughly 60–80% of total heating load in a well-sealed greenhouse. Understanding this number gives you a foundation for budgeting, heater sizing, and cover material decisions.

Add 20–30% to any estimate for infiltration losses through doors, vents, and structural gaps, and you will have a realistic seasonal budget for most operations.

Understanding Heating Degree Days (HDD)

Heating Degree Days (HDD) are the most useful single number for estimating seasonal heating loads. An HDD measures how cold it is over a period of time by counting the degrees below a baseline temperature each day. In the US, the standard baseline is 65°F (18°C in Canada and Europe, where 15°C is common).

If the average temperature on a given day is 45°F, that day contributes 20 HDD (65 − 45 = 20). A mild day with an average temperature of 60°F contributes 5 HDD. A day above 65°F contributes zero — no heating needed. Summing all the daily HDD values over a heating season gives you the annual HDD for your location.

HDD data is available from NOAA (climate.gov) and Environment Canada. Search for your nearest weather station and use the 30-year normal for planning. Some typical ranges:

• Mild coastal (Los Angeles, CA; Portland, OR): 1,500–3,500 HDD
• Moderate (Kansas City, MO; Columbus, OH): 5,000–6,000 HDD
• Cold northern (Minneapolis, MN; Calgary, AB): 8,000–10,000 HDD
• Severe cold (Fairbanks, AK; Winnipeg, MB): 13,000+ HDD

The difference between a mild and cold climate is enormous. A greenhouse in Minneapolis costs roughly three times as much to heat per season as the same greenhouse in Los Angeles — all else equal.

Cover Material U-Values — The Insulation Multiplier

The U-value of your cover material is the single biggest variable you can control at construction time. U-value (in W/m²/K or BTU/h/ft²/°F) measures how quickly heat passes through a material per unit of area per degree of temperature difference. Lower U-value means better insulation.

Here is how common greenhouse cover materials compare:

The practical implications are significant. Upgrading from single polyethylene to double poly reduces conductive heat losses by about 41% — for the same greenhouse and heating system, you will burn 41% less fuel. Upgrading from double poly to 16mm triple-wall polycarbonate reduces losses by another 43%.

However, better insulation comes with trade-offs. Triple-wall polycarbonate transmits only about 50% of light compared to 85–92% for single poly. In low-light winter climates, this can slow plant growth and increase supplemental lighting costs. For heated propagation or seedling houses where light is supplemented anyway, the insulation benefit usually wins. For fruiting crops in short-day winters, the light trade-off requires careful analysis.

Comparing Fuel Types: What Does a Season of Heat Cost?

The same greenhouse can cost dramatically different amounts to heat depending on fuel type and local prices. Here is a practical overview of the four main options:

• Natural gas — The most common choice for commercial operations with gas infrastructure. Priced per therm (100,000 BTU). Typical efficiency for modern heaters: 80–92%. Very price-stable in areas with well-developed gas networks. Not available in rural areas without distribution lines.
• Propane (LPG) — The alternative where natural gas is unavailable. Priced per gallon; one gallon contains about 91,500 BTU. More expensive per BTU than natural gas in most markets, but widely available. Tank rental adds to operating costs. Propane prices are more volatile than natural gas.
• Fuel oil (#2) — Common in older heating systems and in regions where oil distribution is well-established (much of New England). Priced per gallon; one gallon contains about 138,700 BTU — more energy-dense than propane. Requires on-site storage tanks.
• Electricity — Resistance heating is 100% efficient (no combustion losses), but electricity is typically 2–4 times more expensive per BTU than gas or propane in most US markets. Heat pumps are a different story: they can achieve 300–400% efficiency by moving heat rather than generating it, making electricity competitive in moderate climates.

Fuel prices change frequently and vary significantly by region. The calculator uses your local price — always enter a current quote from your supplier rather than using an online average.

Reading Your Heating Cost Estimate

The calculator returns three key numbers, each useful for a different purpose:

• Seasonal cost (USD) — Your estimated annual fuel expenditure for heating. This is the bottom-line budget number. Remember to add 20–25% for infiltration losses and margins not captured in the glazing-only formula.
• Fuel consumption — The number of therms, gallons, or kWh estimated for the season. Use this to negotiate bulk purchase contracts, size your propane tank, or estimate your carbon footprint.
• Heat loss rate (BTU/h per °F) — This is your design heating load, used for sizing your heater. A heater rated in BTU/h must exceed this number times your design temperature difference (how cold it gets at night vs. your target growing temperature). For example, if heat loss rate is 1,000 BTU/h/°F and you need to maintain 60°F when it is −10°F outside (70°F difference), you need a heater rated at least 70,000 BTU/h.

This estimate covers conductive and convective losses through glazing only. It does not model infiltration, solar gain, thermal mass, or night curtain savings. For detailed energy modeling, ASHRAE Standard 169 and University of Vermont Extension publish greenhouse energy analysis tools and guidelines.