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.