Hey guys, Brand new member here... Be gentle. Have been lurking around the forums for the past few months and have learned lots!!
To start off... We installed a new Crown TWZ125 oil fired boiler back in October 2009 feeding baseboard convectors in an approx. 3500 sq. ft. stone home built in 1951 in Philly Pa. My question is: I would like to possibly underfire the burner a bit. How small a nozzle can I use before I need to worry about changing the air tube length?
The boiler consists of:
Beckett AFG burner with a: V1 head
Air tube combo is: 70MDAQ
Static plate is: 2 3/4
Insertion length is: 2 1/4
There is no low firing rate baffle.
Pump pressure is: 140
The factory nozzle is: Hago 1.00/60B
Head setting is: 0
With the outside temp at 30 degrees, the current setup seems to run the burner temp up to 180 degrees from a cold start in about 20 mins, then the burner shuts down. The two circs. continue to run. The temp drops to the 165 degree differential in about 10 mins. Then it starts the burner again and hits 180 in about 10 mins. It continues this pattern until the thermostats are satisfied upstairs. Stats are set back over night to 60 and then set to 68 degrees in the A.M. It typically takes about 1.5 hrs. to reach 68 degrees from 60. This is telling me that the burner/nozzle is oversized. Would reducing the nozzle size enable more efficient burns?
As a side note, I installed the Intellidyne HW+ in Dec. 2009 and the thing is telling me that it is currently economizing 33.6% since Dec 5. The HW+ extended the differential down into the 150 degree or so range before the burner fires again. Any thoughts??? Thanks in advance.

 

Sounds like it's running ok. If it was going something like 2min on and 20 off then you got issues. How does it run when you're closer to design temp, like when it's 5 degrees and real windy outside?

 

Sounds good to me also. You want a minimum of 7 minute run times. I would leave it alone. The second thing is it is not good to under size a nozzle. Has to do with fireside heating surface and input rate. Some boilers you can get away with it as it depends if the boiler is at the upper side or lower side of this ratio. The code limits you to 10% if allowed by the manufacturers.
BTW 8 degree setback is a bit extreme. I would limit it to 5 degrees. I have heard soem say 3 degrees.

 

I agree with the others about the existing run times. I did check Crown's web site to see how much difference there was in the 090, 100, & 125 models. The 125 uses a different air tube combination than the others & seems to be at or near the low end of the firing range.

 

Thanks for the input guys. I've read some posts on here that stated a boiler that is closely matched to the heat loss of the home will run continuously for about 40 mins. or so and then shut down the burner and continue the circs. The theory being that the longer run time is offset by the reduced fuel consumption of the smaller nozzle. Actually. we haven't had any 5 degree days here in philly yet, so I don't know what kind of burner run times to expect when we really get cold here. I'll have to wait and see. I guess I should wait at least a season before making any changes.
rbeck... Could you elaborate on why it is extreme to set back 8 degrees overnight? Is it a condensation issue? Or, something else? I don't want to do any damage to my new boiler. Before replacing the boiler last Oct. I was using approx. 1,200 gals. of oil per year and was desparate to reduce consumption any way possible, hence the 8 degree setback. The old boiler was a circa 1951 Sinkler/Stott boiler with a 1970's vintage updated Beckett burner with a 1.35 gph nozzle. So, the new Crown with a 1.00 nozzle is already using less oil. Of course, I also eliminated the summer/winter hookup and installed an electric water heater with a timer that limits water heating time to about 4 hours per day. 2hrs. in A.M and 2hrs. in P.M. I estimate that I was using about 350 gals. of oil solely for heating water. I've seen maybe a $15 increase in electric bill... not bad in my opinion.

 

You are in luck, Philly will be at design temperature (15 F) for the next three nights. Can use a simple wall clock on the burner motor leads to record the run time. Set the clock to noon/midnight before you hit the sack, then check it in the morning.

Al.