Power vent timing

3 minutes is a good start

I sold a lot of power venters and a 90% condensing oil furnaces. Like it or not the minimum post-purge we could get by with to eliminate smells and after-drip was 8 minutes. Gas can get by with 3-5 minutes not oil.

The furnaces I sold came with 5 minutes timers and we had to change everyone to 8-10 minutes.

Much of it had to do with the combustion chamber radianting back into the airtube and heating up the oil in the drawer assembly and creating a delayed afterdrip. This was discovered by a rise in the CO readings more than 30 seconds after the burner shutdown. Sometimes it just had to do with smells and overcoming negative building pressures.

Field Controls has an adjustable post-purge timer on their PVO Power Venter for oil and it goes up to 10 minutes, thanks to me. I am sure with a really short flue 3-5 might work but not on longer flues. 8 minutes work every time to prevent the combustion chamber from radiating enough heat back into the airtube and eliminating afterdrip. Without testing for CO for at least a minute after shutdown you wouldn't know if you had this problem or not. That is when trial and error on setting the timing began.