How to Heat a Greenhouse in Winter
Inside my Connecticut greenhouse heating system, from the radiant floor to the water loop. Explore the numbers and see how greenhouse size changes heating demand.
Explore the heating system
Adjust the values. The calculations and illustration respond as you go.
Water-side BTU transfer
My recorded water readings are preloaded. Drag the controls or type your own values.
This is a calculated water-side heat transfer estimate, not verified sustained heater output. The installed heater has a nominal 30,000 BTU/hr rating.
Your greenhouse dimensions
Starts with a 16 × 16 ft combined footprint. Sidewall height, roof shape and covering values are editable example assumptions, not verified measurements of my structure.
Estimated heat demand
Estimated air leakage: 1.08 × airflow (CFM) × ΔT. Illustrative gable shape; actual heat loss depends on the real construction, thermal bridges, wind, and ventilation.
An animated look at heat movement
Greenhouse proportions adjust to your values. Arrows are illustrative.
Use the Heat loss tab to change greenhouse dimensions and the indoor or outdoor temperature. The visual updates automatically.
Calculated transfer vs. greenhouse demand
Two separate estimates. Water-side transfer is not the same as verified available heater capacity.
Can my heater keep up?
To compare actual capacity with estimated heat loss, enter a verified delivered heating capacity for the complete system. Do not use the water-loop estimate or a fuel input rating as proof of capacity.
Watch the greenhouse heating series
Follow the real construction and testing process across eight parts. Muse should insert only verified episodes from my video library or official accounts.
Heating series • Part 1
The verified video URL has not been added yet.
The equipment in my setup
These are the equipment categories I use. Muse should match my exact product models to existing verified affiliate catalog records before enabling product links.
How my greenhouse heating system works
In Connecticut, winter heating is one of the challenges of growing tropical plants in a greenhouse. My setup combines a natural-gas blue-flame heater, stainless-steel tubing functioning as a water heat exchanger, a circulation pump, and half-inch PEX tubing beneath a gravel floor.
The warm water moves through the floor loop while the gravel adds thermal mass. Reflective insulation sits beneath the radiant-floor assembly. This guide explains the arrangement and provides tools for exploring the heating calculations.
1. Understanding the water-side BTU formula
My recorded figures for one calculation were 7.66 gallons per minute, 90°F supply water, and 80°F return water. For water, a commonly used approximation is 500 × gallons per minute × temperature difference. That gives 38,300 BTU per hour of calculated water-side heat transfer.
2. Estimating how much heat a greenhouse needs
Heating demand depends on exposed surface area, the covering's overall heat-transfer coefficient (U), the temperature difference, and air leakage. The adjustable calculator above demonstrates those relationships. The example values are assumptions for exploration, not a site-specific heat-loss survey.
3. Why the floor matters
The radiant tubing runs under gravel, so the floor participates in storing and releasing heat. The amount of usable heat depends on the materials, water temperature, layout, and real conditions. It is important to distinguish thermal storage from heat generation.
4. Important safety considerations
Gas-burning appliances in enclosed structures require proper combustion air, venting and carbon-monoxide protection consistent with the manufacturer's instructions and applicable codes. A heat exchanger near a gas appliance also requires professional review. This article describes my setup; it is not instructions for modifying or bypassing gas-appliance safety systems.