5b. Re: 4a. Re: Hot Attic/HRV

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Jeff

Wow a comment from the guy I most respect on this board!

Getting people to clean filters is important and to do maintenance is also important. CMHC has a CE (in the About Your House series) on just that subject. The purpose of the filter in an HRV is only to protect the core, not protect the people (just like a furnace filter is to protect the furnace, not the people). Dirty filters and cores can grow all sorts of things, mold being only one of the not-nice things. If people are going to have good indoor air quality they have to clean filters; even clean houses, or am I just wishfully thinking.

I have a Data Sheet on how to construct an air filter that would really clean incoming air, for those with significant sensitivities, but no one has built one so far because they might cost too much, and being sick is not sufficient reason to spend money. Good inlet filtration is also available, for more money, from Therma-Stor, who make good stuff.

Jim H. White SSC

5b. Re: 4a. Re: Hot Attic/HRV Posted by: "Jeff May" jeff@... jmhiaq Date: Thu Jul 27, 2006 10:01 am (PDT)Jim, I would like to underscore your "except for cleaning and maintenance" with respect to heat recovery ventilation (HRV). Perhaps things are different in Canada but every HRV I have ever opened up (with the exception of one or two) had a mold problem. None of the units I have seen had adequate filtration; the filters, often loose, should be airtight at the perimeter and be at least MERV 8 rating. The intake blower is usually dirty (due to inadequate filtration) and sometimes moldy as well. Some units have condensation that is not properly accounted for. Often there is moldy fibrous liner (insulation). In most cases, the filter on the intake side is full of mold and critters. In two cases, an HRV unit was turned off after years of operation and occupants experienced immediate relief of allergy symptoms. Do you recommend an intake filter at the interior (out of the weather) but close to the exterior wall to keep the intake duct clean? C. May, M.A., CIAQPMay Indoor Air Investigations LLC1522 Cambridge StreetCambridge, MA 02139www.mayindoorair.comwww.myhouseiskillingme.com Jim H. White writes: > Barb> I do not like fresh air intakes very much but prefer HRVs, which can be set and forgotten (except for cleaning and maintenance) if they are installed correctly. In many locations where air conditioners are used, they must then be supplemented with good efficiency dehumidifiers, to control indoor humpty problems in spring, summer and early fall. Modern 'supposedly efficient' air conditioners do not dehumidify well enough, even though that is what air conditioners are really for. > > Depending on the location of your fresh air intake, it could have moved the balance point between inflow and outflow up or down along the inside walls of your house. In the cooling season, if the intake 'looked like' it were low down (a likely scenario), it would have been a massive exhaust down low and the house would have sucked very hard on the attic, bringing down all of the wonderful 'stuff' up there into your breathing air indoors - not too smart. Why is it that 'Americans' believe that if one intake helps, two will be better - that is not the way most people think around the world, where 'just right' in size is an accepted concept?. We Canadian Americans often think that way too. We are becoming more US American all the time. > > By the way, the symptoms that you had remind me of massive mold exposure to mold, something I experience when doing some house investigations. When I am exposed to Stachybotrys chartarum, I also cannot think straight for days, often missing days of productive work. Yesterday I got a minor Stachy hit and I am as cranky as Hell! Sorry about that! > > By the way. the house pressure DIFFERENCE was negative up top and positive down low. Only with large fans operating between the inside and outside (not circulation fans indoors) does the whole envelope see totally positive or negative pressure differences, then there is still the 'stack effect' gradient superimposed, so the effect is not uniform anyway.> Jim H. White System Science Consulting