Low Cost Blower Door

Heat loss through “air changes” - air flowing out of a house through draughts, vents and holes - is huge. An old and unimproved house might have 4 air changes every hour. For a typical 3 bed house on a cold 0 degree C day, that means 6 - 8kW being lost through leakage alone.

The actual energy cost is incredibly variable, so I wrote an interactive tool to calculate it.

At the new gas price cap of 7.37p/kWh, that means as much as £14.15 a day spent heating air which blows out the house.

The industry standard method of testing for air leakage is the blower door. This is a large fan which is sealed across and opening (usually a door) and which blows air into the house until the house is 50 Pa above ambient pressure. The airflow is then measured, and an air leakage rate (in m3/hr/m2 of floor area) can be calculated.

All new build houses must have this test done, but most older houses never do.

Current blower doors are made by a few manufacturers. They’re expensive (£2000+), bulky, and make use of lots of complicated equipment (eg a laptop running specialised software). Typically someone might hire them out for a few hours to perform a test.

During a test, draughts and holes reveal themselves. A smoke pen or incense stick can be used to find these. Even small holes will result in a fairly big draught at 50 Pa.

There would be a big benefit to low cost, accessible blower doors.

  1. They could be set up permanently and used regularly while hunting down leaks to improve a house
  2. Sealing draughts would become an instantly measurable activity - the feedback loop would be minutes rather than months

The components of a blower door are quite simple.

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