Downfire a Utica 4-Section Starfire

NTL1991

Brainstorming a bit to save my senior mother a little on her heating bills this winter.

The boiler is way oversized. It's a Utica Starfire III SFH4150WT which originally had a 1.25-80B nozzle, netting 175k BTUH. At some point, my brother (a steamfitter) put in a 1.10-80B nozzle, which it's been running for years, netting 149k BTUH.

4 Zones:
Downstairs- 24K BTUH
Upstairs- 20K BTUH
Patio Room- 14K BTUH
Basement Fan Coil- 13K BTUH
Total Heat Loss: 71,000 BTUH

The boilerplate lists another option, a .85-80B nozzle, netting 120k BTUH, which appears to be the lowest official firing rate for this 4-section boiler. According to the specs, I'd just need to swap in an F3 burner head (no doubt it probably still has the F6 head in it...) the new nozzle, and have my brother come over with his meter to set up the air and draft with his UEI.

Is that going to be the closest we can match this boiler to the house? Last year I installed a wired outdoor reset to the Honeywell L7224. I have a new Taco BumbleBee laying around, would I see any efficiency boost running that on Delta-T mode?

STEVEusaPA

4150 calls for F5 (? I think its a typo and should be F6) head, 150 psi, 1.25 X 60W.
You can downfire as long as your not condensing, but I never recommend downfiring. My feeling is burners should be fired at their rated/tested settings.
Condensation on both the fire side, and cool return water temps are the biggest boiler killers.
No one's ever proved to me that there is an actual savings as you trade efficiency for the appearance of the boiler running less.
Now the next problem is ODR. ODR, plus an oversized boiler just doesn't work without a buffer tank. Actually it never works without a buffer tank as you need the boiler to get above 140° and most of the time the control will be targeting minimum temperature (140°) to 160°, until you get colder temps. So your boiler will short cycle alot, never spend much time above condensing, and become a mess to clean, as well as shortening it's life.
The only solution is to fire it as recommended. Protect the boiler from low water return temperatures, install a buffer. Nothing else will really show any savings, and like I said create more harm than good.
Even the smallest boiler is too big, especially zoned.
An Energy Kinetics would be the best option.

Steamhead

Many boilers give the option of using one of several firing rates. As long as the boiler is officially rated for that lower input- which is the 0.85x80B nozzle at 140 PSI IIRC- and the proper burner head is used, you should be fine. Always run the combustion test afterwards to make sure it's running safely and efficiently. Stack temperature should be above 325°F to keep the flue gases from condensing.

HVACNUT

You would essentially be making it an SFH4100, but as you can see, changes are needed. 

NTL1991

Thanks guys. I figured it would be allowed since those options are both listed on the boiler spec plate. I am curious to see what head is on there, the original F6 or a correct F4 for the current 1.10x80B nozzle. I'll have my brother verify the pump pressure, set up the air and draft with his meter after the new parts are in.

Does anyone have the part number for the correct air tube for the 4100 with F3 head?

Any thoughts on swapping in the BumbleBee for the 007? It wouldn't take much time at all, and it's just laying around on the shelf.

STEVEusaPA

IDK what you are expecting the bumble bee to do for you , but it will probably make your short cycling worse.
The air tube number is on the chart @HVACNUT posted, assuming it's the same size block/chamber.