poster3814,

Very glad to try to help you answer your question. In researching this
matter, I also found your post in the home do-it-yourself web site forum,
and hope you have been able to get some additional insights.

Having installed humdistats of both the "outdoor sensor" type (the later
model Aprilaire) as well as those of the earlier type (Sears, Aprilaire,
Autoflow), no doubt it is much simpler to install a humidistat directly in
the furnace plenum with no wiring going to either a separate humidistat
upstairs in the heated space or wiring going to an outdoor sensor. The time
saved in not wiring, and also time saved in not mounting an outdoor sensor,
adds up to at least an hour or two, maybe more. It is my belief that the
Honeywell solution appeals to installers for this reason.

The extra labor invested in installing an outdoor sensor and wiring it seems
to pay off well, based on the limited sample of systems I have had in this
house. Not until I installed the outdoor sensor Aprilaire did I truly reach
the total automation I was seeking, where the dew point is dynamically
adjusted and there is never, ever, ever,.....any moisture, frost, or dew
forming on my windows or anyplace else, yet the humidification is always
extremely comfortable with none of the problems arising when there is too
little humidity. My kids were prone to allergies when they were young, my
wife complained on dry skin, we frequently drew big sparks as we walked
across the carpets, and drawers and doors would begin to stick. The outside
sensor eliminated any misadjustment issues entirely.

As to whether a Honeywell Humidicalc with no outdoor sensor sitting in a
basement cold-air return plenum can infer enough from the surrounding air
and plenum temperature / humidity to make really appropriate guesses about
what the dew point is remains to be seen in my opinion. Given the option of
a direct measurement of outdoor temperature versus a software algorithm
which, at best, knows only current and past temperatures, and current and
past humidity local to the duct, it is hard for me to imagine a superior
outcome, particularly since the Aprilaire humidistat also sits in the same
location when installed and also has humidity and temperature data to work
with, or so it appears. Moreover, Honeywell also adds an optional outdoor
temperature sensor when controlling either multizone or heat pump systems,
since in either / both cases the local duct measurements are insufficient.

Good luck with your decision and glad to be of help. I am sorry for the
digression which occurred in this thread earlier regarding energy needed to
evaporate water.

Smarty






"poster3814" wrote in message
link.net...
wrote:
Smarty wrote:
Thank you very much for your replies, and the time, etc., spent on them. I
appreciate it. Other helpful opinions from knowledgeable people are also
welcome.

Thank you.
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