cold air coming from registers in ceiling

[maximus]

Hello,
When I built my house, I placed the furnance in the attic since I had so much unused room. I've notice cold air coming from the registers when the furnance is not running. Clearing, the cold air is coming from the attic. I have metal duct work which is insulated. I've checked all the duct work and everything seems fine. I'm at a lost to what I can do to stop the cold air from coming in.

 

[elkimmeg]

Todays Insulation standards in Ma require higher r values for insulation duct work located out side the insulation envelope. Due to your furnace or exchanger's location, it gets very cold above your attic insulation, with all the required ventalation of that space. Extra considerations and precautions must be taken to prevent the cold air from entering the duct work and filtering into the occupied space. Your system must be lacking them When it is opperating producing heat hold your hand around the unit to detect leaks Silver duct or HVAC tape can be used to seal the leaks also caulking. The same leakes the heat escapes are, the places cold air infiltrates. Check both the supply and return sides

 

[Roospike]

Just the metal duct work in the "cold" attic will get the air in the duct work cold and the cold will drop even if if the duct work has no leaks. Its just like the stairway in a house ... the heat goes up the stairs and the cold comes down the same stairs at the same time. Im sure that if the duct work was insulated that it would have less of a chance to get cold. If the duct work stays warm then no cold / less cold would drop .