Oversized steam boiler - worth replacing?

elfie

what is rough cost to replace a 10 yr old cast iron steam boiler (14 section)?  the existing boiler has a capacity to produce 3 million btu's per hour.  the new steam boiler would be about 1 million btu's.



ideally, it would be better to install 2 smaller steam boilers each about 500 btuh each.



thanks

JStar

Well

We do not discuss pricing in public. Where are you located?

elfie

another way

maybe another way to approach this dilemna is to ask it in another way.



if you had a steam boiler with a capacity of 65 million btu's per day and you were only producing 10-15% of this amount on the coldest of winter days, does it make economic sense to replace boiler?  do people buy used cast iron boiler sections?



the boiler probably has another 20+ yrs of life.  yes its costing a few thousand more per yr to run, but the payback is probably 15-20 yrs, which is too long.  So, I guess the only course is to endure more costly energy bills for the next 20 yrs.



I suspect many are in a similar situation.

Charlie from wmass

The boiler may not have that much life left

I am finding many over sized poorly piped commercial boilers that are failing after 6 or 7 years. How do you know the proper boiler size? Did you do a radiator survey of the building? On that size of boiler a staged burner with a vapourstat controlling it may be better to cut costs. What is the current boiler make and model? It may simply need a staged or modulating burner to give you big savings.

elfie

burner control

here is the burner pic (powerflame) for boiler (HB Smith) and related pressuretrol and cutin/cutoff devices (ie. controlling burner intensity and burner cutoff/cutin).  cutoff pressure is set at about 2.5 psi.  all the short cycling is unfortunate (purging is inefficient) and auto setting results in lower burner intensity but still short cycles.



does all this represent a staged burner setup?



is a boiler failure (shorter life) more likely due to severe overcapacity?



also, have done a radiator sizing exercise and found that btu delivery capacity within space (one large room) being heating is one fifth of the boiler capacity (room is easily heated with existing rads)



thanks

Charlie from wmass

can you take a photo

from further back on your burner? It may be two stage but it needs to be properly tuned to save fuel when changing fire rate. also has the water seal been cleaned out for the pressuretrols?

elfie

burner and pressuretrol settings

better picture of burner



i doubt the water seal on pressuretrols have ever been cleaned, what would this do? never heard about cleaning the water seal





basically, all this boiler is doing is ultimately supplying steam to two 2 inch pipes that connect to blower heating coils - each blower is 3000 cfm (ie. a 3 million btuh boiler).  



thanks very much

Charlie from wmass

It would stop them from working

I am refering to the 1/2" piping below the pressuretrols. Yes that is a two stage burner. It starts at a 50% down fire and can be down fired even further. Where is the boiler?

elfie

boiler pics

front and side view of boiler and the headers



would down firing the burner resolve the excess capacity issue - how tough would it be to downfire the burner



thanks

Charlie from wmass

for me or another trained burner guy it would be easy

but easy is relative. Yes that is a reason the boiler is designed for staged firing. I have not walked in on a burner that was actually set to fire two stages even though a two stage boiler was paid for.

elfie

two stage

how would i know if its set for two stage functionality



i am aware that the burner modulates, is this the same as two stage functionality?



thanks

nicholas bonham-carter

Modulation-the cure for oversize?

Is this system your's, or a client's, or perhaps a possible purchased building? What maintainence has been performed on a regular basis? Has it been losing any water?

My suggestion would be to have the burner(and boiler), serviced so as to make the modulation functional and see how it behaves. You can observe how it is working by watching the pressure on an accurate gauge. The fan-coil units may require a bit more pressure than regular radiators. A 0-4 psi vaporstat could be able to control the modulation of the burner, if you are lucky, but with the potentiometer, only a real expert like Charlie would know. Consulting the online documentation for the burner would tell you a lot about it's possibilities.--NBC

elfie

steam coil pressure

good point about higher pressure needed for steam coils.



thanks