Thursday, October 4, 2012

Fresh Air Is Free

Fresh air is free. Heating it and handling it is necessary and affordable where there is not ridiculous excess. The cost of heating in a forced hot air system is not the heating of a small amount of fresh air. It  is primarily the cost of heating surfaces of floors, ceilings, walls, windows and doors, with the circulated air. Here is the math for my house.

My natural gas usage averages 300 therms per year, for the past six years. I choose to apply a cost of $2 per therm, as expressed in my web page, Insulation Math. The $2 per therm gas cost is $600 per year.

Here, I assessed the quantity of fresh air I receive, 1330 CFM50 in a 1000 sf single-story home. I reckon ACHnat at the high end of the desirable range of from 0.25 to 0.5  changes of the house air volume, per hour. This is slightly more than I want.

The Insulation Math converts this blower door result, to a heating cost, as 0.074*CFM50, about $100 per year. One sixth of my annual heating cost is for the fresh air, and a lesser fraction is voluntary. I am in the midst of upgrades in my home that will at last tighten things, by perhaps 500 CFM50. I'll still have enough fresh air. I will save less than $40 per year by the tightening. I will save a LOT more by insulation measures, completing the insulation of outside walls by interior drywall tear-down, and sealing/ conditioning my crawl space. I have new, airtight heat ducts in the crawl space, and I don't need a jerk with a duct blaster to prove the air tightness. My new 95% efficiency gas furnace will become more effective where the steel header from the furnace is lined, and individual registers are served by flexible ducts. The savings include leakage elimination and, much more importantly, the elimination of the old steel ducts heat capacity sucked up in each cycle.

The picture of relative significance of fresh air cost and losses through windows and walls is very similar, for the very dissimilar Uphill House, in upstate New York. About $100 per year  to heat air, of a total of about $500 per year for all heating costs.

We call the lie then of this statement in the October 2012 issue of HBA News in Portland, Oregon:
Air leakage is the largest source of heat loss in most homes. Warm air leaks up and out openings high in the house, creating low pressure and sucking cold air through the openings low in the house.
The lie is necessary to the continuance of a Home Performance Industry, all those believers that all weatherization is in the numbers of blower door tests. Tell lies, and then go on to commit fraud through conflicts of interest and the can of foam trick, evidently taught and sponsored by the HPwES program developers.

The HBA News lie is expressed verbatim  in a release by Upper Valley Heat, in Lebanon New Hampshire. I don't think HBA News got their text from Upper Valley Heat.

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