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10-12-2011, 09:50 PM #27Regular Guest
- Join Date
- Aug 2011
- Kingston, Ontario
Another thing I have so far had trouble finding here, is anyone who has a Ductblaster. I guess duct leakage is just not a big thing here with most ducts in conditioned space. I would have liked to have the duct leakage tested before insulating, but it seems only way will be blower door test which I have scheduled for later in year once house sealing is complete (another project!). It's a bit too late then so just hope our sealing is good enough!
We are hoping to get average of R12 insulation on ducts - Maybe lose 1250BTU/Hr on cold winter days? Not so bad. But IF we have say 100cfm leakage with outside air at 10F and heat pump discharge at 100F, wouldn't that mean we would lose 9720 BTU/Hr of the units 38000 btu/hr capacity? If so, on those cold days, we lose about 11,000 btu/hr. to attic. Ouch!
At 10F, COP for our unit is 1.9 and it consumes about 5.9Kw (20k BTU/hr) in producing 38,000 btu/hr of heat. But because of losses, we only get 38-11=27k Btu/hr. In effect COP has dropped to 1.35
Does this seem right?
10-13-2011, 03:56 PM #28Professional Member*
- Join Date
- Jun 2011
- Wake Forest, NC
If you want to get through to the contractor on how important this is then ask him to do a proposal for a complete duct sealing and they will almost surely be happy to oblige. In lieu of that you will get about 1/2-1 hour of helper with a bucket of mastic, and I can't fault the contractor for that.
Good luckIt's not rocket-science...
It's electromechanical thermodynamic engineering