You can use these type furnaces as a stand alone.
Necking down the duct work restricts your air flow and keeps the firebox hotter. Change your duct so it's 8" all the way to the register and it should keep the furnace cooler.
It sounds like there may be other problems but I wood start with the duct work.
Necking down the duct work restricts your air flow and keeps the firebox hotter. Change your duct so it's 8" all the way to the register and it should keep the furnace cooler.
It sounds like there may be other problems but I wood start with the duct work.