I just had an entire heating/cooling system (including ductwork)
replaced and the contractor is urging me to use Honeywell FC40R
I've always used the 80¢ blue spun fiberglass filters and change them
very regularly -- about 12 times a year.
These Honeywell FC40R filters cost a lot and don't have a particularly
high MERV rating. I have two return air grills and the price for two
of these filters will be about $150. The contractor says I should
change them every 6 months or $300 a year. WOW!. That's a *LOT* more
that the cheapie filters I've been using.
My questions are:
Since I have two filters rather than one they load up less. How can I
tell if the filter *really* needs replacement? I didn't mind throwing
away 80¢, but the idea of throwing away $80 unnecessarily -- be still
Is the protection afforded by these Rolls Royce priced filters really
going to do enough to pay for themselves, or is this just a "feel
good" thing? [We don't have allergies and have been happy with the
air quality with the cheapie filters]
FWIW, recently I was involved with modifying blueprints submitted by a
mechanical engineer for multiple mechanical systems for a client. The
mechanical engineers design called for .1 static on the main sa & ra
ducts, with a .08 for the branch ducts. Granted, most of the pkg
units are belt drive, but typically .1-.08 are very common duct sizing
If you ever get an opportunity to attend a class on Trane's
Residential zoning, by all means attend. Or for that matter any
manufacturers zoning class that incorporates 0-100% modulating
dampers. You'll see designs on the branches around .04-.05.
FWIW, I design between .06-.08 on all branches and .08-.1 on all
plenums & trunks.
Awhile back I had an extremely interesting situation.....an airhandler
running at 20,000 cfm was pumping air into a cleanroom. In the clean
room were 12" HEPA's, and in the air handler were 2" pleats. About
20% fresh air was being pulled in by the air handler.
The supply from a 10 ton hp was ducted to the return plenum on the air
handler. Right next to the supply was the return duct back to the 10
My job was to install another 5 tons into the very same air handler
return plenum. Once I tapped the new ducting into the return plenum,
the static pressure was so great in the 5 ton pkg return compartment
you had to struggle to get the access door back on. Obviously I went
with a 1hp high static blower motor for the new 5 ton unit.
I guess my point is, sometimes you gotta do what you gotta do, even if
its outside your normal comfort curve of experience or training.
The .7/.8 were just averages I pulled from my fleeting memory. Quite a few
times the SPs went over 1.0". I was
theorizing that units running for extended periods at High Static Pressures
would see premature unit failures.
It's been a dozen years since I've done any installations but I have had to
go in after and re-duct to bring the SP
down to .5". When I was installing (mostly Trane units using flex!) I never had
any difficulties keeping the .5" SP
pressure required. In the repairs I have made almost all of them were because
of undersized R@ ducts (hacks) or some
type of electrostatic filter. I don't know if I buy the idea of a wet coil
always being = .3".
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