Downsizing boiler

HeatJockey

I have an apt. house customer that we are converting from oil to gas. The boiler didn't "feel" right, so I checked the actual installed load. The boiler ( Smith 28-6) is actually over twice the installed radiation.  I have 3 options:

a)  install a new boiler, if the customer is willing to spend the money

b)  install the burner sized for the oversized boiler and short cycle

c)  install the proper sized burner (for the load)  The boiler will make steam, but will the flue temps be too low?



I don't think removing sections from the boiler is cost effective.   

 The gas piping run changes from 2" to 3" because of the different loads.



Sharing any experience you might have had would be appreciated.  Thank You

Charlie from wmass

Contact Smith

They will know how far you can down fire. Some boilers they allow 50% down fire. You could also use a two stage or modulating burner. This would give you a fast recovery yet let you down fire to stop short cycling. Do not forget to use a vaporstat.

nicholas bonham-carter

Oversized boiler

With such an oversized boiler, maximumum main venting would reduce the short-cycling. A 0-3 psi gauge would tell you when you had reached the open-pipe equivalent. Making sure the radiator vents were slower Hoffman 40's would help.--NBC

HeatJockey

Thank you all for your advice

I spoke to Smith and they did say that the boiler can be downfired up to 50%.  I now have a plan.

Dave in QCA

50% should be good

I installed a WM 680 last December.  It is firing on low fire at about 390 BTU, or pretty close to 50%.  The reason for the oversizing has to do with future plans to restore the old garage and chaufferer's quarters back to the steam system.  But, for the time being, firing about about 50-60% the boiler is perfomering exceptionally well!  Running about 30% less than the 1975 Pennco that it replaced.