Ducting in attic - http://www.hvacmechanic.com/ Forums
Original message
| jerichocraftsma
 |  "Ducting in attic"
, posted Sun 9 Nov 16:02  
A customer in a new (2yr old) home asked my opinion as to how to lower heating costs in winter ($700-$900 per month) as they keep there thermostate at 64, 60 at night and when they are away. Developer put in propane forced hot air for whole developement and every owner is complaining (go figure). They did an independent HVAC audit and changed some return ducting in the attic but did little to help. I noticed the blown insulation in the attic is only about 11" deep and all the ducting is suspended above the insulation. I suggested the depth of the insulation be increased and was curious as to wether the ducting, and especially the flexible, be dropped to the trusses so it could be enveloped into the inulstion. I am curious as to if this is advisable, and if not, why? Is there an issue with access, or moisture build up. The insulation around the flexible duct is R4.5
Alex
Alex
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Replies:
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| frankout
| "Re(1):Ducting in attic" , posted Sun 9 Nov 16:22
It could be a number of things. First the duct should be droped and blown over with insulation. It's probably not your contractors falt. There some cities that make you strap it up (they don't understand that its a heat loss and a miss service for the home owner) Example would be putting your beer in a cooler or leaving it out side. The other thing could be tne insulation around the duct is r4.5 in most places codes are going to R8. It also could be windows, wall insulation, doors and ect. The cost of propane has gone up also. You could get a heat camera and see were your losing heat on the home.
frank
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| Freon
| "Re(1):Ducting in attic" , posted Sun 9 Nov 16:11
Maybe a complete heat loss analysis would be a good first step. You know the insulation values and the exposure. You should come up with a BTU/hr amount of energy lost at a given outdoor temperature. Calculate the heat loss for each month's median outside temperature. Then you will have an idea of the energy use. Now price the propane cost for those BTU requirements assuming an 80 or 90% efficient furnace. If there is a huge discrepency, then further investigation is needed. It might be propane in that location is very expensive and the heating/insulation are doing their job.
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