"John Doe" wrote in message
...
Bought a cheap humidity meter, really enjoying it. Its main purpose
combined with a dehumidifier is to help keep the humidity under 50%.

The inside humidity seemed to follow the outside humidity until about a
week ago. It was dry. But then very humid. Ninety-six percent outside for
the last several days and yet the humidity inside has remained less than
45%. Today it was up to 45% but now it's down to 40% even though it's 80%
outside.

We use a gas heater. Is that the cause?

Thanks.

You can't expect the inside humidity to exactly follow that outside. The
relative humidity is not only a function of the amount of water vapour in
the air, but also of the temperature. The water vapour content of air that
enters the house from outside will then be subject to sources and sinks that
will produce large local variations in different parts of the house, and
these will persist for a time which depends on the movement and mixing of
air inside the house. Sources would be any open water source, including
steam from cooking, shower or bath water, open cups of liquid, humans and
animals, plants etc. If the water is hot or boiling, it can supply
relatively large amounts of water vapour in a short time. Sinks could
include fabrics, wall paper, dehumidifiers, and the materials of the house.
Some of these could also be sources when there are temperature variations
inside the house. The gas boiler should not be able to change the water
vapour content of the air in the house, unless it is faulty. All the water
vapour produced by the burning of gas should be efficiently expelled by the
built in fan, together with the toxic carbon monoxide.

--
Bernard Burton

Wokingham Berkshire.

Weather data and satellite images at:
http://www.woksat.info/wwp.html



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