Code:
Filter Manufacturer & type VS. Pressure Drop
Filter IWC MERV
Purolator KP-STD1-0301 1" Deep 0.24" 7
Purolator SYN-RG-2430 4" Deep 0.12" 8
Purolator HE40HC-STD1 1" Deep 0.24" 8
3M 300 0.15"
3M 600 0.14"
3M 1000 0.21"
3M 1500 0.18"
3M 1900 0.21"
3M 2200 0.21"
Typical cheap furnace filter 0.1"
*All 3M filters are 1" deep.
*IWC = Inches of Water Column. Lower is less restrictive.
Don't have MERV ratings for the 3M's. To help put this into perspective, I only had a ESP (external static pressure) of 0.3IWC to begin with in designing my new duct system. Using one of the Purolators or the higher end 3M would have cut my ASP (available static pressure) down to ~ 0.05IWC and I still have to account for pressure drops from DX coil, electric heat coil, supply outlet, balancing dampers, return grill, etc. In other words, I'd be left with a negative ASP, which won't work! So I'd have to increase the blower speed or use another filter and recrunch the numbers.
The 3M 300 has 40% less restriction than the purolator, right out of the box! As they get dirty, the more restrictive each will become. In a furnace, the heat exchanger will get really hot because there's not enough airflow over it, the over-temp switch will engage, your house will be cold and you'll wonder why.
Here in Tx where we only have two seasons: Summer & January, your evap core will likely turn into a block of ice due to lack of airflow, liquid refrig might make its way back to your compressor (especially if you don't have a TXV) and damage it or shorten it's life. Your house will be hot and there'll be very little air coming out of the vents. Meanwhile your indoor blower will be pulling against the block-of-ice (so to speak), the rpm's will greatly increase, it'll get really hot and greatly shorten its life.
And all because some ad on the filter said "this one will clean your whole house!". Bravo Sierra. No, it won't. Don't buy into the marketing hype. All the filter does is keep your furnace or evap coil and blower vanes clean. That's all.