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Re: GSBN:HRVs and SB


I would agree with what Derek and others have said about indoor air quality, etc. I would even go so far as to say that I wish our codes would follow yours and require HRV's, because then I could actually get people to use them, instead of cutting them at the last minute, as is generally the case. I say "almost" wish because requiring them flat-out would be an excessive expense for some people who are building small houses on a very tight budget. (So now we come back to the heart of your question.) I assume that the generally enlightened Canadian codes make provision for use of energy modelling software, so that if you can show that a given design will meet the overall intention of the code with the use of exhaust-only ventilation (bathroom fans with timers) rather than an HRV, I would imagine that you would be OK. Of course, it may turn out that an HRV is a less expensive way to meet the code than having to bump up to (for example) those Canadian triple-paned fiberglass windows. (Which we have only used once so far, but which work supremely well, in terms of both heat loss and noise reduction.) Such provisions sometimes also account for size, allowing a slightly less efficient envolpe and sysstems for small houses, since small houses use so much less heating energy than large ones.

So now that I've gone in a bit of a circle about that, I will disagress with Derek's assertion that "current heat recovery ventilation systems are primitive and expensive." They are somewhat expensive, but I would certainly not call them primitive. They ventilate an entire house with only a 30% heat loss, using 1 moving part- a very high quality fan. They have filters for incoming and outgoing air which can be specified to remove pollen, dust, urban pollutants, and other matters of concern to allergy sufferers, chemically sensitive people, children, etc. They replace the bathroom fans, so there is no noise in the bathrooms. They provide some circulation of interior air. And they lead to houses in which the air is warm but also always fresh and clean. Regardlesss of building materials, I have never been in a house with an HRV that didn't have sparkling air quality. So given all of that, and considering that they are built to last indefinately, I don't think they're very expensive.



Lacking comments from Rob Tom and Paula Baker Laporte, here is what I think about indoor air quality. Moisture buildup is not the only problem. It may be the most serious issue for the physical structure of the home, but it is probably secondary for the health of the inhabitants.

For good indoor air quality, a home needs significant, continuous air exchange in all rooms. This is hard to achieve. If a building has lots of air infiltration, it wastes energy and can lead to invisible moistuure problems in the walls. A loose home is also likely to have very uneven air exchange. If a building is tight, then air exchange needs to be designed in, in order to have healthy air quality in all rooms, regardless of moisture levels.

Current heat recovery ventilation systems are primitive and expensive, which is why we don't want to use them. But to ignore the problem and subject ourselves, our families and our clients to unhealthy indoor air is irresponsible.


--On Thursday, January 23, 2003 10:03 AM +0200 Evgeny Shirokov iae@... wrote:

From my experience with straw-clay houses: moisture is not a problem
in bathroom, if you use clay stucco and protect walls from "direct
water flow" by ceramic or other with ordinary system of ventilation.

And Chris Magwood relayed:
Has anyone with a strawbale home NOT installed a heat recovery
sytem (HRV) and if so do you have a problem with condensation?
I'm trying to decide whether to install one before my interior
walls are closed in.

Now that HRVs are part of our building code, it seems
inspectors are not giving owners any options other than
installing the full systems ($3-6000 and require constant fan
noise and energy, plus ductwork everywhere). Does anybody know
of an indoor air quality expert who might have options/opinions
other than the installation of full HRVs? My own home was built
without one, and we don't have any moisture problems, which I
attribute to the amount of porous, unsealed natural materials in
the house (barn board, beams, unpainted gypsum plaster, etc)
which are capable of a lot of storage when conditions are
humid, and release when conditions are dry.

Derek Roff
Language Learning Center, Ortega Hall Rm 129, University of New Mexico
Albuquerque, NM 87131  505/277-7368, fax 505/277-3885
Internet: derek@...
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Paul Lacinski
Amy Klippenstein
GreenSpace Collaborative
Sidehill Farm
PO Box 107
463 Main St.
Ashfield, MA 01330 USA