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Comment by Rick Karg on June 26, 2014 at 9:04am

David, I am the guy who put together and narrated the video.I am sorry you missed the section in the video about increased heating load resulting from ventilation, which was 6.4 therms (slide 9). I did mention the increased cooling load, but did not include it in the SIR calculation because of the location; Portland, Maine, where cooling is a minor issue. If you use this analysis in a heating/cooling climate, both the heating and cooling load increases from ventilation should be included in the SIR equation numerator. The RED Calc Free Advanced Infiltration tool reports both heating and cooling loads.

Regarding maintenance, you are correct, I did not include any maintenance costs. If these were included they would be subtracted from the numerator as a recurring annual cost and would lower the SIR value. I ignored these costs because we don't have a good idea of what they are. Of course, there will be some homeowner work involved, such as cleaning the ventilation fan blades, etc. We hope to get a better idea of maintenance costs for ventilation systems within the next five years or so.

It is best practice to add ventilation to each room using ductwork, as you suggest, but it is not required by the ASHRAE 62.2 standard. I assumed a high quality exhaust fan installed in a centrally located bathroom would provide local and whole-building ventilation (this complies with ASHRAE 62.2). If the ventilation system is more complex, the cost of installation would increase. This would, of course, impact the SIR value. A ventilation system that distributes fresh air evenly throughout a home is preferred. However, it is common that this best-practice solution will not fit into the project budget, especially for the folks working within the low-income weatherization program.

Comment by David Eakin on June 26, 2014 at 8:20am

You did not add the (other) expected yearly running costs for the ventilation unit (additional air conditioning costs for heat/coll/dehumidify, any replacement parts/service, etc.) in the initial SIR computation; you only talk to the fan electrical costs. Also note: if the structure does not already have duct work (a very common occurrence in older buildings) the additional ventilation duct work costs make this proposal very costly, and assuming a single exhaust fan will provide adequate ventilation to each individual occupied room - especially with closed doors - without dedicated duct work is problematic regardless of what the ASHRAE prescriptions preach. It is the reason why paired supplies/returns are the best way to deliver conditioned air to each occupied room vs. central supplies/returns.

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