These are good, been to a couple of flats where these were installed but tenant had switched it off though, they didn't like paying for the electric to run it.
I deal with this issue for Landlords frequently. It isn't always easy for a tenant to keep it clear, have had situations with insufficient insulation, old windows without trickle vents, leaky roof etc. On the other hand, often have the situation where tenant is drying clothes on radiators, has...