Changing nozzle size in hot water boiler

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Old 09-14-18, 09:58 AM
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Changing nozzle size in hot water boiler

I have a 30 year old Peerless WB3 hot water boiler with a 1.1 gal per hour nozzle that is rated at 129,000 Btu gross output and 112,000 water Btu I did a whole house load calculation using the site Load-Calc.net and came up with total Btu heating of 84,000 for a design outdoor heating temperature of -10 F. The house is located about 11 miles from Burlington, VT airport. There is another label on this boiler with a 0.85 gals per hour nozzle rated at 102,000 Btu gross output and 89,000 water Btu I was thinking of putting in a 0.85 nozzles to reduce fuel oil cost. Can I just change out the nozzle or are there other adjustments to the system that need to be made? I also get DHW from the system. Thanks for any feed back.
 
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Old 09-14-18, 10:38 AM
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A combustion test will have to be done when changing nozzle size.
This is something that should be done anyway at least semi-annually even if not changing the nozzle size.
 
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Old 09-14-18, 03:43 PM
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ed,
The first question I have is, have you physically seen the 1.1 nozzle or is that what the ticket says. I ask because to my knowledge there is no such nozzle as a 1.1. That oil rate is achieved by raising the pump pressure.

You may have a .85 there already with a pump pressure of around 120 psi instead of the normal 100 psi factory set oil pump. They raise the pressure for better atomization and to increase the pressure of a lower gph nozzle.

Check your nozzle first to see what is installed. Next, what burner do you have. Is it a Beckett or Carlin or some other brand.

It makes a difference because you may need a possible head change on the burner tube.

At the very least you will have to change the air setting and as mentioned and should be set up with a combustion analyzer for proper combustion.

Hope this helps a little.
 
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Old 09-15-18, 06:20 AM
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Dope Slap

spott was correct, there is a 0.85 nozzle in place already, so my question was made mute. Thanks to spott & roughneck77 for your help and getting back so quickly.
 
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Old 09-15-18, 09:02 AM
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The most accurate way to find actual boiler load is to clock boiler run time over a period of days.

Wire a elapsed time clock to boiler solenoid circuit. https://www.ebay.com/itm/Hour-Meter-...8AAOxymmJTkKlH

Log the degree day count at start and end of period. Divide number of degree days for the period by hours run to find degree days per hour. If your design temp is 0 F then that is 65 degree days. Divide 65 by your dd/hour to find run time required on design temp day.

Many old homes with boilers sized years ago are oversized because of added insulation, new windows and other improvements. My 60 year old boiler fired at 50% of rated BTU runs 8 hours/day at design temp.

Smaller nozzle results in lower stack temperatures and higher efficiency. I also use lower deltaT on aquastat/outdoor reset to avoid long run times which result in higher stack temperatures.

By logging gallons used during time period, degree days per gallon can be determined. That is what oil companies use to schedule deliveries.

If boiler also supplies domestic hot water the dd/gallon will be slighly higher in colder weather.

Clocking actual run time data is more accurate than using heat load calculations and boiler/nozzle rates. It is real data. Allows determining actual nozzle gph flow rate. Charts showing flow at different psi show calculated, not actual flow rate.
 

Last edited by doughess; 09-15-18 at 11:29 AM.
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Old 09-17-18, 06:54 AM
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Hour Meter Method

Thanks doughess,

I just in stalled a similar hour meter last week. I am looking to replace the house boiler and will use your recommended method to help determine the sizing. thanks again.
 
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Old 09-17-18, 09:07 AM
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To get boiler BTU I use stack temperature vs efficiency chart on Beckett Guide page 33 figure 26 and 140,000 BTU gallon

GPH x 140,00 BTU/Gal X Efficiency = BTU/hour

https://www.beckettcorp.com/wordpres...to-Oilheat.pdf
https://www1.eere.energy.gov/manufac...efficiency.pdf

On any boiler, the lower it is fired the higher efficiency. It is often better to go to larger boiler with given nozzle size. Boilers get dirty and are less efficient than when new.
 
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