"SteveB" wrote in message
...

"ransley" wrote

You realy cant put an hour or date on replacing them, If you have
pets, keep windows open and dont clean often it wont last long, maybe
3 months, and I have seen them nearly clean after 1 year.

EXACTLY. Some seasons when it's nice weather, one hardly turns on the HVAC.
Like you say, different people have different environments. Pet dander. Dust.
Lots of things. It is absolutely impossible to give any rule for changing
them EXCEPT change it when it's dirty.

It's like asking about how the weather will be tomorrow. It all depends on
where you live, don't it? It's not all the same.

The thermostat "monitors the number of hours on the air filter".

What part of that don't you understand?

Bob