Thank you , Robert for the system you installed. The furnace works better and keeps us warmer with no cold air at the start. Also the thermostat works better, allows more flexibility and registers the correct temperature in the hall. I checked the filter last week (2 months after changing the filthy first one) – looks clean as new. I think maybe our return ducts must have been very dirty and the AC blower must have displaced it all so the filter caught it.