I am installing a new energy efficient furnace and ac. I have been sealing up the house quite a lot. The HVAC contractor wants to install a 6″ duct to the outside connected to the cold air return side to create positive pressure in the house. On the surface this seems like a big energy looser. I looked on the American Lung web site and they recommend 10 minuets of fresh air every hour. I have seen devices that accomplish this and this seems to make more scene to me. I know this been hashed out a lot here but the HVAC guy keeps coming back to the same idea. Am I missing something. Thanks Jay
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Replies
You should only need a breathing tube for the furnace and an exhaust for same. Don't burn warmed air if you can help it cause then it needs replacing and this works against energy saving.
If you house is that tight the air could become stale, then a air to air exchanger with heat transfer is used to provide fresh air.
High efficient furnace = Direct Vent - use concentric vent with intake air directly to combustion. Otherwise use an HRV (Heat Recovery Ventilator) for tempered fresh air - http://www.trane.com/Residential/Products/AirCleaners/FreshEffects.aspx
Jeff
he's not talking about combustion air and exhaust, he's talking about a fresh air supply to the cold air return, which is good. If you want to be more energy efficient you could install an HRV (heat recovery ventilator) and exchange some bad air for good ..
I know what he's talking about but if a furnace or boiler has it's own intake for combustion air the heating plant at least achieves neutral pressure, whereas taking combustion air from the house itself pulls in drafts around doors and windows.
Jeff
Perhaps a little outside air ducted into the cold air return system would be beneficial. The trick is to not overdo it. Introduce too much outside air and you reduce the suction available to move air from the conditioned spaces back to the furnace, thus reducing circulation.
Also, if your house is super tight, once the positive pressure is built up, it has nowhere to go, and you cease to both bring in outside air or circulate it within the house.