Hi diyhome, If you have solid external walls you are probably best sealing the outside air brick - as a trial, cut a piece of ply to fit over it and seal it in place. See what then happens over the winter. Regards S
"I understand most condensation issues are caused by insufficient ventilation." correct, however air must circulate, i.e. in and out, the heat recovery unit is likely best option.
There are other causes like a brick tie wrong way up. Normal cure for that is put water repent on outside walls.
In the old days out open fires used air in the room for combustion, this caused natural ventilation, we also sat in high backed chairs to stop the draft, and paid a fortune for heating.
What we tend to do is look in isolation, mould in bathroom so fit a fan with no thoughts as to where the air will come from, i.e. no vent in door to allow replacement air.
A vented tumble tumble drier blows air out of the house which needs replacing, but we fit doors with good seals to stop drafts, worst is gas cooking, we know gas when it burns produces water, but so often there is no cooker hood, which is essential with gas to remove combustion products.
Step back and look at house as whole, how will air circulate, both inside to outside and room to room. Too much is also bad, our first house had hot air central heating, we had to put trays of water into the air intake to stop static shocks.
I note in summer our AC removes gallons of water. Yet the humidity meter shows 62% which if anything is low.
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