How much heat does a Wichita greenhouse need each month?
Heating degree days (HDD) measure how cold a season is relative to a base temperature. NOAA's 1991–2020 normals for Wichita Eisenhower Airport give 4,592 HDD a year at the standard 65°F base.
Base 65°F is built for houses. A greenhouse held at 45°F only needs heat when it is colder than 45°F. Lower the base and the degree days drop. NOAA publishes Wichita's normals at those lower bases too, so no guesswork is needed.
The table also shows the heat a 12 × 20 twin-wall greenhouse needs each month (model below) and the gas cost at the example price.
| Month | HDD 65°F | HDD 55°F | HDD 45°F | Heat at 45°F (MMBtu) | Heat at 55°F (MMBtu) | Gas at 45°F | Gas at 55°F |
|---|---|---|---|---|---|---|---|
| October | 231 | 68 | 12 | 0.16 | 0.90 | $2 | $14 |
| November | 576 | 303 | 107 | 1.42 | 4.01 | $22 | $61 |
| December | 911 | 603 | 313 | 4.14 | 7.98 | $63 | $122 |
| January | 986 | 676 | 379 | 5.01 | 8.94 | $77 | $137 |
| February | 767 | 492 | 250 | 3.31 | 6.51 | $51 | $100 |
| March | 550 | 278 | 97 | 1.28 | 3.68 | $20 | $56 |
| April | 277 | 90 | 15 | 0.20 | 1.19 | $3 | $18 |
Source: NOAA NCEI 1991–2020 monthly normals, USW00003928. December and January carry more than half the season. At 45°F, January alone is roughly 30% of the winter's heat.
The model: U × A × HDD × 24
Seasonal heat loss (BTU) = U × A × HDD × 24
- U is the glazing's heat-loss coefficient in BTU per hour, per square foot, per °F of difference.
- A is the total glazed and wall surface area in square feet.
- HDD is degree days at your setpoint. The 24 turns degree days into degree hours.
Example greenhouse: 12 × 20 ft, freestanding, 8 ft sidewalls, gable roof with a 4 ft rise.
- Sidewalls: 2 × 20 × 8 = 320 sq ft
- End walls: 2 × (12 × 8 + ½ × 12 × 4) = 240 sq ft
- Roof: two slopes of √(6² + 4²) = 7.21 ft, × 20 ft each = 288 sq ft
- A = 848 sq ft (floor excluded)
U-values used:
- Single glass: 1.13 (NGMA)
- 8 mm twin-wall polycarbonate: 0.65 (NGMA, winter value)
- 16 mm triple-wall polycarbonate: 0.45, a design value between NGMA's 0.58 for 16 mm structured sheet and the 0.40 one manufacturer lists
Worked line, twin-wall at 45°F: 0.65 × 848 × 1,273 × 24 = 16.84 million BTU.
Setpoint × glazing: the season at a glance
| Glazing (U) | 45°F setpoint (1,273 HDD) | 55°F setpoint (2,658 HDD) | 65°F setpoint (4,592 HDD) |
|---|---|---|---|
| Single glass (1.13) | 29.3 MMBtu / $448 gas | 61.1 MMBtu / $936 gas | 105.6 MMBtu / $1,617 gas |
| Twin-wall 8 mm (0.65) | 16.8 MMBtu / $258 gas | 35.2 MMBtu / $538 gas | 60.8 MMBtu / $930 gas |
| Triple-wall 16 mm (0.45) | 11.7 MMBtu / $179 gas | 24.4 MMBtu / $373 gas | 42.1 MMBtu / $644 gas |
Two things fall out of the math:
- Setpoint: going from 55°F to 45°F cuts heat 52% (1,273 ÷ 2,658 = 0.48).
- Glazing: twin-wall cuts conducted loss 42% versus single glass (0.65 ÷ 1.13 = 0.58). Triple-wall cuts another 31% versus twin-wall.
Compare glazing options in detail on our polycarbonate vs. glass page.
What do gas, propane and electric heat cost in Wichita?
Every price below is a dated example input. Replace it with your own bill.
Evergy (electric). The Kansas Corporation Commission approved a $128 million Evergy rate increase on September 25, 2025, effective with the October 2025 billing cycle. The KCC put the impact at about +$8.47 a month for a residential customer using 900 kWh. We do not quote a per-kWh rate because seasonal tiers, riders and fixed charges make any single figure misleading. Assumption for this page: 15¢ per kWh, all-in. Replace it with your bill's total divided by its kWh.
Kansas Gas Service (natural gas). The commodity portion of your gas bill changes every month under the Kansas Gas Service Monthly Net Cost of Gas tariff, which applies to all Kansas rate areas. Delivery and customer charges are added on top. For an all-in example we use $12.69 per thousand cubic feet, the EIA Kansas residential natural gas price for January 2026. EIA's summer monthly averages run much higher because fixed charges spread over fewer cubic feet.
Propane. Example input: $2.074 per gallon, EIA Kansas residential propane, week of October 19, 2026. Your delivered price depends on your contract and tank.
Conversions from EIA: 1 cubic foot of gas = 1,036 BTU; 1 gallon of propane = 91,452 BTU; 1 kWh = 3,412 BTU. Combustion heaters assumed 80% efficient.
| Fuel | Example input | Cost per million BTU delivered | Twin-wall season at 45°F | Twin-wall season at 55°F |
|---|---|---|---|---|
| Natural gas, 80% | $12.69/Mcf (EIA, Jan 2026) | $12.69 ÷ 1.036 ÷ 0.80 = $15.31 | $258 (20.3 Mcf) | $538 (42.4 Mcf) |
| Propane, 80% | $2.074/gal (EIA, Oct 19 2026) | $2.074 ÷ 0.091452 ÷ 0.80 = $28.35 | $477 (230 gal) | $997 (481 gal) |
| Electric resistance | 15¢/kWh (assumption) | $0.15 ÷ 0.003412 = $43.96 | $740 (4,936 kWh) | $1,546 (10,305 kWh) |
| Heat pump, COP 2.5 | 15¢/kWh (assumption) | $43.96 ÷ 2.5 = $17.58 | $296 (1,974 kWh) | $618 (4,122 kWh) |
When does a heat pump beat gas?
A heat pump delivers more heat than the electricity it uses. That ratio is its coefficient of performance (COP). A heat pump breaks even with a fuel when:
Break-even COP = (electric price per kWh ÷ 0.003412) ÷ (fuel cost per million BTU delivered)
| Electric price (assumption) | Electric cost per MMBtu | Break-even COP vs. gas ($15.31) | Break-even COP vs. propane ($28.35) |
|---|---|---|---|
| 10¢/kWh | $29.31 | 1.91 | 1.03 |
| 12¢/kWh | $35.17 | 2.30 | 1.24 |
| 15¢/kWh | $43.96 | 2.87 | 1.55 |
| 18¢/kWh | $52.75 | 3.45 | 1.86 |
At our 15¢ assumption, a heat pump must average a COP above 2.87 over the season to beat gas, but only above 1.55 to beat propane. COP falls as outdoor temperature drops, and January nights are when a greenhouse needs heat most. Check the manufacturer's low-temperature performance data, not the rated COP. If your site has no gas line, a heat pump is usually the cheaper electric option. If gas is already there, it is close.
How big a heater do you need?
Seasonal cost and heater size are different questions. Size is set by the coldest night:
Peak load (BTU/hr) = U × A × (setpoint − outdoor low)
Twin-wall: U × A = 0.65 × 848 = 551 BTU/hr·°F. With an assumed 0°F night:
- 45°F setpoint: 551 × 45 = 24,800 BTU/hr (7.3 kW if electric)
- 55°F setpoint: 551 × 55 = 30,300 BTU/hr (8.9 kW if electric)
Wichita's normal January low is 22.5°F (NCEI), but design nights run far colder. Size for the cold snap, not the average. Use a heater rated for greenhouse use, vented to the outside if it burns fuel.
Methods box
- Climate data: NOAA NCEI 1991–2020 normals, Wichita Eisenhower Airport (USW00003928). HDD at bases 45, 55 and 65°F are NCEI's published values, not our approximation. NCEI computes annual and monthly normals separately; the monthly 65°F values sum to 4,414, below the 4,592 annual figure. Seasonal totals here use the annual figures; the monthly table uses monthly figures.
- Geometry: 12 × 20 ft, 8 ft sidewalls, 4 ft gable rise, A = 848 sq ft. Floor losses excluded.
- U-values: NGMA suggested coefficients (single glass 1.13, 8 mm structured sheet 0.65); 0.45 triple-wall design value as noted.
- What the model leaves out: air leakage (adds heat loss, more in wind), daytime solar gain (reduces it on sunny days), night curtains, and thermal mass. Treat results as planning estimates, not guarantees.
- Prices: EIA and KCC figures as dated above; 15¢/kWh is an assumption. Heat output is what the greenhouse needs; fuel bought = output ÷ efficiency or COP.
How to cut the number before you pour a footing
- Pick the lowest setpoint your crop tolerates. Cool-season greens at 45°F cost half what 55°F does. See which crops sell in winter in our Kansas winter markets guide.
- Buy better glazing once. Glazing is the U in the formula.
- Shrink A. An insulated, opaque north wall swaps U = 0.65 glazing for a far lower insulated value. Our passive solar designs do this.
- Store daytime heat. A climate battery moves surplus afternoon heat into the soil for night use.
- Watch the footprint. Our 240 sq ft example sits over Wichita's 200 sq ft permit exemption. Check the permit guide.
Frequently asked questions
How much does it cost to heat a greenhouse in Kansas?
For a 12 × 20 ft twin-wall greenhouse in Wichita at 45°F, about $258 a season on natural gas at the January 2026 EIA Kansas residential price, $477 on propane, or $740 on electric resistance at an assumed 15¢/kWh. Size, glazing, setpoint and your actual prices change that.
Why not use the 4,592 degree-day figure directly?
Because it assumes a 65°F setpoint. A greenhouse held at 45°F sees only 1,273 degree days in an average Wichita winter, per NOAA's published base-45 normals. Using 4,592 for a 45°F house would overstate heat by about 3.6 times.
Is a heat pump worth it for a Wichita greenhouse?
Against propane or resistance heat, usually yes. Against natural gas, a heat pump must average a seasonal COP above about 2.9 at 15¢/kWh. Run the break-even formula with your own rates.
What is the Kansas Gas Service cost of gas?
It is the monthly commodity charge Kansas Gas Service passes through for the gas itself, set by its Monthly Net Cost of Gas tariff. It changes every billing month. Delivery and customer charges are separate.
Does the Evergy rate increase change these numbers?
The September 2025 KCC order raised a typical 900 kWh residential bill about $8.47 a month. Use your current bill's all-in cost per kWh in the formula rather than any published rate.
Ready to build?
- Geothermal and climate battery greenhouses: store daytime solar heat in the soil, with honest payback math.
- Polycarbonate vs. glass glazing: choose the U-value you will pay for every winter.
- Passive solar greenhouses: insulated north wall and mass to shrink the heating load.
- Custom greenhouse construction: footprint, foundation and glazing sized for your lot.
Get a quote
Send us your footprint, setpoint and fuel. We will run this model for your design and build to it.