Additional testing of DIY MERV 13 and indoor air quality Australia Day Long Weekend

As the smoke rolled in on Sunday night I put my particle counter outside and watched it peak at 170 PM2.5 outside.

Car

I took my particle counter on a drive and I found in the i30 I was driving it was around 10, while outside when I left was 30. I had AC on full. It seems the car filter does filter out some of it.

Indoor Air Quality

Some observations:

• Living area leaks the most. It does have sliding doors, 2 pocket doors, lots of down lights, and a range hood. I'm not surprised.
• Rumpus fared a bit better. Interestingly it followed the living room's rises but to a lesser extent.
• There was a slight increase upstairs. I had 2 purifiers running in 2 rooms, but not in the room I measured. It seems it benefited from the purifiers in the other rooms.

The smoke rolled in around 8PM, and it took close to 4 hours for rooms to start exceeding 25 PM2.5.

DIY MERV 13 Filter

I repeated my DIY MERV 13 test however with the sensor on the opposite side of the room.

The two readings are quite close. I tweaked the expected CADR from 70% to 75% to get a better fit. If correct the DIY filter is working even better than my previous calculations.The outside level on Observed 1 was 35, while it was 88 for Observed 2. This might be why Observed 2 finished slightly higher.

Ducted AC Filter or No Filter

I had a theory that removing the rock catcher filter may be better as less restricting means less sucking in of outside air. However I found no meaningful difference with or without the filter.

Positive Pressure Ventilation

I've often thought instead of having air leak in I should pump filtered air in.I tried putting a HEPA filter in the window and a fan to draw air though. In theory this would need less ACH to get a great result. In reality it was a failure as it lowered the room from 24 to 15 after 1 hour. Once I put the DIY MERV 13 on it it quickly dropped to 4. I suspect I had some leaks, as any leak would be bad as its only a 1 pass filtering system. I measured the air flow through the filter to be 175m3/hr so it was bringing in air.