Over sized boiler

Rookie

This boiler is oversized the load for home heating is about 35,000 with a 50 gallon indirect.That's why i went down to the .65 nozzle, changing to the .85 will raise usage and possibly back to the short cycle problem, if the .65 doesn't keep up, I'll bump it up.What do you think good plan ?, or am I wasting my time, and just go with the .85 nozzle.Thanks for all your help, heating season is around the corner.S.H.C

Rookie

Need some idea's

Looking for help on some modifications for a heating system that may help with the short cycling and large fuel consumption problem.The house has about 879 square feet on the first floor with about the 728 sqft in the finished basement apartment,the first floor has each bedroom zoned and the basement has two zones,after a heat loss the house has a loss of 35,061 btu, the emittors on the first floor are burnham cast iron baseboard, with fin tubed baseboard in the basement apartment. The present boiler is a Slant Fin XL-30, with a beckett burner, plus an 50 gallon indirect ( electric water heater converted to an indirect using a flat plate heat exchanger) the boiler has a firing rate of 1.00 gph, 80w nozzle and is running about 140 psi pump pressure, the output looks to be adjustable to 105,000/120,000.The present system looks to be over sized, looking to downfire this boiler or add a buffer tank. Any ideas would be appreciated.Happy Labor Day.

Unknown

Hi Jim,

You can fire that down to .85, and use the set-up for the XL 30H.

http://www.slantfin.com/boilerpdf/XL40.pdf

A buffer tank would definately help, too.

You might try a trick called master zoning, if you have zone valves on that system. On the real short zones, disconnect the end switch that brings on the pump and boiler. Let the valve open and close with the thermostat action, but only bring up the boiler when the big zone calls. Put one thermostat and valve from each apartment on the boiler as a master for each occupant, and let the rest of the zones ride the curve. The burner will see bigger loads, and the rooms will synchronize their timing to all begin together.

Noel

Rookie

Buffer Tank sizing

Is there a buffer tank sizing chart, what type of tank?

Marty_7

Heatmanager

A Beckett Heatmanager can also help you by extending the running time of the boiler. Short calls for heat can be satisfied without the boiler running in many instances.

Good luck

Ron Schroeder_3

any indirect DHW tank

with an internal heat exchanger coil will transfer more BTUs more quickly resulting in longer run time and less cycles.

The is no substitution for a proper heatloss calculation. Matching the BTU developed by your boiler to the actual losses of your home will save fuel and wear and tear on your equipment.

In my experience it is possible to make comfort and performance gains using a 4-way mixing strategy in installations such as yours, thus "stretching" the between times of your heating cycles. It's just a thought.

Sometimes too, if the discrepancy is great enough it is worth considering a radical surgical approach. A high water volume, low temperature boiler with an appropriate mixing valve and outdoor reset can provide significant gains so as to justify the expenditure incurred. It depends upon your needs.

JOHN_103

i've used the heat manager for this reason it will help
and save a few dollars .i would buy the second sensor for
the hot water pipe coming off the in-direct even though
beckett says its not needed

Ron Schroeder_3

accoring to the experiences of those Wallies

who kindly responded, the Heat Manager's efficacy is in some dispute...

Rookie

Hey Noel

I'm trying to squeeze this beckett,so I downfired to a .65 nozzle, we adjusted to bring it up to about to 83.9%,Excess Air-34.8%,Stack temp-476f,primary temp-86f,o2-5.7%,co2-11.3%,co-63ppm,co air free-87ppm.I was running a slight trace maybe a #2 smoke, I think I'm pushing it too far, but I will find out, always looking for input, I realize that I need to retest in novemebr to adjust to the winter air..The Heatmanager, before I go that route I will install a Riello burner.Thanks.

Unknown

Too much excess air

Your stack temp will be MUCH lower and your "mileage" will be better with the .85 nozzle. I think that's as good as you can do for them.

The real answer, of course, is that no buffer tank or down-firing, can make up for over-sizing a boiler.

If you try to size a buffer tank from a sizing guide, do you size it to the too-big boiler, or the not-big-enough system?

There's no right way to do it wrong.

Noel

Guy_6

Firing

Is that .85 nozzle recommendation based on 100 psi or the stated 140? If it's 100, he can drop either the pressure or nozzle size and get even lower output.
I'm not questioning your suggestion, just pointing out something that may have been overlooked.

Wayco Wayne_2

I've had good success

with a buffer tank. Had a job someone way over sized a brand new system. I re piped the system and made it a primary secondary and ran the primary through an 80 gallon electric water heater. Increased firing time and coasted on thermal mass a good long time. Helped lots. WW

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Unknown

The setup specs

are included in the manual attached above. The .85 is the actual firing rate.

Noel

Unknown

I think a lot of your fuel is going up the chimney

and that's why the cycles are longer. Longer cycles don't always mean lower fuel bills.

.85 is the smallest firing rate I'd use.

Noel

Ron Schroeder

If you use the newer Honeywell electronic triple aquastats or most of the outdoor reset controllers, you can set your high limit differential to a higher amount than the usual fixed 10 degree differential of conventional controls. With oversized boiler/burner combinations, increasing the differential will often give as much savings as outdoor reset.

I have been quite successfull in underfiring boilers but it often requires changing the retention head, static plate or adding a low fire baffle or some combination of the above. I have fired an AFG at .3gph at zero smoke and 12% CO2 in a boiler designed to fire at 1.5gph. Of course, the low limit on the aquastat must be set at above 125 degrees to prevent condensation and the flue must be properly sized to get enough draft.

Ron

hr

After you have

done as much as possible to downfire and adjust the burner, consider some water side help. There is a buffer tank sizing program in the HDS. It allows a lot of what if inputs. I've had good luck with properly applied buffers in micro zoned systems, specfically copper tube fired ones

Siggy did a class on short cycling in Vegas a few years back. Some good info in that presentation if you can get a copy.

hot rod

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