This is when you use the Emergency Heat option on the thermostat of a Heap Pump System.

This is how Carbon Monoxide poisoning happens, please get your gas furnaces checked after a new roof is installed.

Animals in the attic is bad news.

This is when you use the Emergency Heat function on your thermostat with a Heat Pump System.

Improper sized equipment, unsealed ducting, poor duct design and installation leads to this.

UV lighting systems also help prevent this.

If you have this, you're breathing it!

Furnace wasn't working, no wonder!