Repair-It

So I guess after probably 4 or more years it's finally time to do an "annual" oil burner service on the house. I don't think I've messed with the burner since you had helped me tune it about that long ago. I do think that's only about 3 or 3.5 tanks worth of fuel, so I've probably "only" run less than 1000 gallons through it. The minisplits carry a large portion of shoulder season heating - seems like I only resort to oil heat when outside temps are less than 30 or so just so I don't have to listen to the mini-splits.

I just ordered 3 new 0.65GPM x 80 deg Delavan nozzles, some more spare filters (I already have a few primary/secondary filters on hand) from supplyhouse.com.

Should come in tomorrow.

Hopefully I can get to cleaning it and changing the nozzle and filters before the "real" heating season starts.

rpaoness wrote: Tue Oct 14, 2025 12:13 pm The minisplits carry a large portion of shoulder season heating - seems like I only resort to oil heat when outside temps are less than 30 or so just so I don't have to listen to the mini-splits.

I reran my numbers for comparing oil furnace efficiency to my mini-splits. The numbers still generally cross over around freezing. Anecdotally, I agree, they seem to work a lot harder as temps dip below freezing. I don't really hear noise (other than some occasional vibration at compressor startup as it ramps up) but running the inverter electronics and compressor hard to barely achieve better cost efficiency than oil does not seem smart to me. So, in practice, I agree, and my numbers agree. Neat.

At my current electric (~$0.28/kWh delivered) and oil rates (Sept top off was $2.85/gal), my furnace does about $3.16/hr per 100k BTU of heating. 1 GPH nozzle (washes out from the 100k normalization), 80% rated minus 10% duct loss, and taking into account electricity use of burner and HVAC fan.

For my great room single zone 18k, it starts off very efficient at only $2.29/hr per 100k BTU of heating with a 68F setpoint and mild 57F outside. This efficiency decreases as outside temps decrease, leading to an increased cost of $2.95/hr per 100k BTU @ 32F, which is still a bit better than $3.16. By 25F, cost is up to $3.09. By 20F, cost is exceeding oil at $3.23.

For my dual zone 18k on the other side of the house, cost is similar at $2.36/hr per 100k BTU at 57F outside and a 68F setpoint. This cost ramps up to $3.13 @ 32F outside which is knocking on the door of oil furnace cost. Yes, my single zone is a little more efficient than my dual zone, at least when ramped up to max output. I do not have efficiency curves for "part throttle" operation, but I would expect it to be a bit higher, since all of the surrounding components are now "big" for the output. However, the fans ramp down which decreases efficiency. Could be a wash??

So yeah, in practice, shutting them off around freezing is sensible. Maybe a little lower, maybe a little higher, depending on whatever. Junk in the condenser (should be cleaned annually minimum but probably twice a year) will decrease efficiency. Same with a dirty inside unit HX.