GBlist: GBList: Winter Ventilation

["Mike Rogers" <mprogers@together.net>]

Judy's article was in JLC, September 2000

It's hard to answer the original question in a general way.  It is possible
to make an existing home very tight.  Weatherization crews in this area
often work with a blower door on the home and stop once they've hit a
certain leakage level.  They could often go tighter, but are usually working
in situations were they will not be able to install ventilation under the
guidelines of the assistance program.  There are a lot things that can be
done to tighten an existing home, and if you're determined, in many cases
you can indeed get to levels were you need to plan for ventilation.  Without
diagnostics--e.g., a blower door test--you won't know where you're at.

A ducted system would most likely be the surest way to deliver outdoor air
to each room.  However, in a heating climate (and it sounds like you'd only
be using mechanicals during the heating season) exhaust ventilation can
work.  In a house this size, I doubt a single exhaust point would provide
effective distribution.  However, you might be able to get reasonable
distribution with multiple exhaust points.  This could be done in different
ways.  You could use bath fans distributed throughout the house, existing
and addition.  Or you could use a modestly ducted central exhaust to pull
from several areas, not just bathrooms.  I believe exhaust only works best
if you have a forced air system which provides periodic mixing of the air.
But in a heating climate, I'll take even poorly distributed exhaust only
ventilation over nothing.

A word on passive vents:  I'm skeptical that they work the way they're
intended.  A study in by the Vermont Energy Investment Corp. showed that air
doesn't necessarily recognize these vents as inlets, but instead follows the
laws of physics!  Air moves from high pressure to low pressure.  So anywhere
above the neutral pressure plane, air will exhaust out of the passive
"inlets".  For example, you'd likely find (as did the study) that passive
inlets on the second floor often acted as exhausts in the winter.  Given the
breezy location, you might also find that inlets on the windward side on the
house admitted a lot of air, while those on the leeward actually functioned
as exhaust during windy periods.  This unpredictability is probably best
avoided.

Consider finding someone in the area who can provide specific
recommendations for the house based on the actual house conditions,
including the measured leakage.

Regards,
Mike Rogers

----- Original Message -----
From: Pesce, Matt <mpesce@aspensys.com>
To: <greenbuilding@crest.org>
Sent: Tuesday, November 21, 2000 11:02 AM
Subject: RE: GBlist: GBList: Winter Ventilation


> EPA and LBNL (Judy Robeson) finished a comprehensive home ventilation
study
> a couple of years ago.  Judy also published an article in the last couple
of
> months in Journal of Light Construction.  (Alternately, it could have been
> Fine Homebuilding or Home Energy--I don't have it handy).
>
> Matt
>
> -----Original Message-----
> From: Charlotte Matthews [mailto:Cmatthews@payette.com]
> Sent: Tuesday, November 21, 2000 10:40 AM
> To: greenbuilding@crest.org
> Subject: GBlist: GBList: Winter Ventilation
>
>
> Green builders,
>
> This email is for those of you with some expertise, or at least interest,
in
> ventilation.
>
> ---- Pre-Summary of Issues -----
> * 4100 SF house + addition
> * Steady breezes, all year round
> * Winterized house, so anticipated air leaks
> * House naturally inclined towards passive ventilation
> * Good chance that major portions of the house will be unused for
> significant periods of time, especially in colder months
>
> CONUNDRUM: Must I install central fan and ductwork, or can I rely on spot
> exhaust and passive vents?


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