Conservatory BTU Calculator

About Conservatory BTU Calculator

A conservatory is the hardest space in a house to condition, and sizing it from a standard per-square-foot rate produces a figure that is nowhere near enough. This calculator uses 45 BTU/h per square foot for cooling and 55 for heating, roughly double the rate for an ordinary room. The reason is that glass is a poor insulator in both directions. In summer the roof and walls admit solar radiation directly, and a south-facing conservatory can become unusable by early afternoon regardless of the outside temperature. In winter the same surfaces lose heat rapidly, which is why so many conservatories go unused for months. Unlike other rooms, the improvements that reduce the requirement are structural rather than incremental: roof blinds or a solid insulated roof, solar control glazing, and thermally broken frames all change the number substantially. If you are sizing for winter use, switch the mode toggle to heating, since the heating rate is the higher of the two and is usually the binding constraint. For an ordinary room see BTU Calculator.

How to use Conservatory BTU Calculator

  1. Enter room area in m² or ft²
  2. Set ceiling height, sunlight exposure, and number of occupants
  3. See recommended BTU, kW, and AC unit type

Frequently Asked Questions

Why does a conservatory need so many more BTU?
Because glass conducts heat far better than an insulated wall and admits solar radiation directly. A conservatory gains heat rapidly in summer and loses it rapidly in winter, so the equipment has to work against a much larger heat flow than in a normal room.
Should I size for heating or cooling?
Check both and size for the larger figure, which for a conservatory is usually heating. A unit chosen only for summer comfort will be undersized in January, which is when most conservatories stop being used.
Will roof blinds reduce the requirement?
Yes, and significantly for cooling. The roof admits the most solar gain because the sun is overhead when it is strongest. Roof blinds or a solid insulated roof are usually the single most effective change you can make.
Is a portable air conditioner enough for a conservatory?
Often not. Portable units are typically 8,000 to 14,000 BTU/h, and a modest 150 square foot conservatory already needs around 6,750 for cooling before adjusting for direct sun. Run the numbers before assuming a portable will cope.
Does the orientation matter?
Very much. A south-facing conservatory takes direct sun for most of the day and should use the high sunlight setting. A north-facing one is far easier to cool but harder to heat, since it gets no useful solar gain in winter.

Related Tools

Also Available As