So I've spent the last two months looking at options to improve the IAQ in the house that we just bought. I've started with local room air purifiers and have shifted to upgrading the central air system. I've come to the conclusion that I could only use an external HEPA with it's own fan but I'd love for someone to confirm my logic.
We have a high efficiency furnace with a variable speed fan (Carrier 58MVP120). Currently we have a Carrier ESP which I have concerns with due to how quickly the the ESP loses it's ability to attract the dust and ozone generation. Our home inspector indicated that he had some concerns with the air flow from our vents but didn't do a full energy balance. The furnace has a nameplate maximum external static pressure of 0.5 in. I was going to measure the static pressure before and after the blower using a Dwyer manometer, but based on some rules of thumb on the web, it appears you don't want to exceed 20% of the furnace rating in the filter pressure drop, which in our case would be 0.1 in. Now based on info on this site the ESP is likely around 0.1 (due mainly to the resistance in the prefilters) and filters like the HC16, Aprilair 5000 etc. have pressure drops that begin in the 0.3-0.4 range and could increase up to 1 in plus when fully loaded.
So it would seem obvious at this point that I couldn't increase the resistance by including a new filter (or replacing the ESP) and that using a self powered HEPA is the solution, while leaving in the ESP. A HEPA was more money than I was hoping to spend but if that's the only way forward, without replacing the furnace, then we'll do that.
The question is am I correct or on crack?
Thanks in advance.
PS Thanks a lot to the frequent contributors to this site...it's been very helpful.