Installed a Tjernlund AD-1 draft inducer for the DF520. I also sealed off the boiler room from the rest of the house, and put in a fan blowing fresh air into the room. The draft is great now, and what a difference in how the boiler runs. It stays burning with temps in the 50s now. I get -0.04 with the AD-1 set to low. I can run it faster, but felt this was good enough to keep the DF520 running in warmer weather.
Only issue I have is what to do when I need to switch to oil when I travel for work. The AD-1 has a big 2" hole around the motor shaft for the fan so suspect I can not turn off the fan when I switch to the oil burner since fumes will come out. Not sure the AD-1 can take the smoke stack temps with the oil burner? I'll have to replace the AD-1 section in the smoke stack with a new section when I switch to oil.
I am also considering installing a chimney liner to help with the draft. Does anyone have any experience with chimney liners? Does the liner just stop at the bottom of the breach where the horizontal flue intersects to the vertical flue to the boiler? I don't see a way to get a tee into the chimney, and still need to drop debris in the ash pit.
I believe a better solution is to install a chimney top draft inducer instead of a smoke pipe draft inducer. Does anyone have a recommendation on chimney top draft inducers? I found this one from fieldcontrols.http://www.fieldcontrols.com/chimneytop.phphttp://www.ddchem.com/Chimneydraftinducer.pdf