rubmeister100 said:
Nope.
Old Wives Tale.
Of course I am familiar with temperature rise. And IF the delta t were increased, then that would seem to indicate an INCREASE in heat transfer efficiency!
The highest performance 3M 1" Filtrete filter has an initial pressure drop of 0.02" H2O. A moderately loaded poly filter is easily 0.75" .
The ONLY thing I can say against the pleated filters is that you have to be more vigilant in changing them.
NOT an old wives tale - 100% true. Like I said before, everyone in the trade knows this - you may be an engineer, or maybe just a know-it-all, but your above comments indicate lack of real-world relevant practical experience.
I am an HVAC/R mechanic; I mainly do commercial/industrial applications but often must do the residential equipment of the owners for which I have commercial contracts.
People buy the 3m filtrete filters as a cheap alternative to an actual HEPA filtration unit (which requires its own motor to overcome the additional resistance of the HEPA filters). The overwhelming majority of high-efficiency residential furnaces require a temperature rise of 45-75F; some are as low as 30-60F. Going back to the 45-75F DT, the average temp rise, with proper manifold pressure and firing rate, is usually around 58-62F. Throw in a 3m filtrete & your DT is now getting pretty close to the allowable upper limit of the manufacturer's spec's. Now, let that filter get a little dirty, since the Home depot guy tells the homeowner that the filter is good for at least 3 months, to justify charging whatever the hell they charge for those things ($25-$30 range?), and add in the fact that many homeowners often do silly things like closing off the basement & main floor supply registers to provide more heating/cooling to the top floor, and in a very, very, VERY short time your furnace will be tripping on the hi-limit switch. Now, if you have an insertion tube fan-limit switch, it will cycle on & off repeatedly - overheating, cooling down, overheating, cooling down, and you the homeowner will likely be none-the-wiser, but brother, you are stressing the hell out of your primary heat exchanger, until one day it cracks. That is not good & will get your furnace A-tagged& shut-down immediately, and it's usually during those -10F days of February. This is extremely common & most people will never be aware of it, until the day a "furnace guy" tells them (of course, with a thermal disc type limit switch it is possible that the homeowner may notice something is wrong in colder weather when the furnace goes into a 3-hour soft-lockout).
So, in my expert opinion, if allergies/asthma is an issue, get a HEPA unit. If you insist on using 3M filtrete, change them at least monthly (unless your house is not actually lived-in, but merely a display model that no-one ever uses & has better than 1992 NBC requirements for outside-air infiltration).
Now, I partly agree with your assessment of "furnace guys", but that's largely due to the same complaint that lots of tradesmen on this board complain about.....homeowners expect Cadillac quality at Kia prices. There are lots of less-than fully qualified "furnace guys" out there who are EXTREMELY busy working residential jobs at $50-$60/hour, because homeowners think the qualified ones at higher prices are a rip-off. Get an HVAC mechanic (or "technician", as is the more popular term), and he will have AT least the equivalent of 6 years of training (if done consequatively - most guys do it concurrently & can be done in 4).
If anyone is interested in seeing the reality of the situation as I've described above, you can often arrange for a ride-along with a HVAC or HVAC/R mechanic if you call up the bigger, well-known companies and ask (tell them you're interested in getting into the trade - the money is excellent and, generally chicks dig us because we are hot guys & cool dudes - that's an HVAC/R inside joke).
And that, my friends, is the final word on this topic.
