Our contractor has recommended a Burnham ES2-4 gas boiler for our conversion from oil. In researching I see that it is a discontinued model, and requires a stainless steel chimney liner, which we don't have. Does this sound right?
Burnham ES2-4
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The ES2-4 doesn't sound right on a number of counts...
The ES2 series has not been discontinued, but there may have been recent changes/updates.
However the 89,000 BTU/hr DOE output of the ES2-4 is ridiculously oversized for most normal sized houses (even if you're also using it to heat domestic hot water), and not the best choice for 19 out of 20 houses in your ZIP code. Even the ES2-3 is more than 1.5x oversized for most homes in NYC (ASHRAE recommends 1.4x oversizing, not more.)
It needs a correctly sized flue liner to be vented into a masonry chimney, but it doesn't need to be stainless.
The ES2 is more expensive than several fire-tube modulating condensing boilers out there that would be a better size fit, even at a comparable higher BTU output, and cheaper to install too.
Take a BIG step back, gather up some wintertime-only oil fill up slips, and first run a fuel-use based load calculation using the oil burner as the measuring instrument to get a handle on your heat load at +15F outdoors (NYC's 99th percentile temperature bin aka "99% outside design temperature".) The largest cast iron boiler should have a DOE output no more than 1.4x the fuel-use calculated number, but not less than that number.
With a modulating boiler there is more flexibility, but the minimum modulated output becomes the more important number. To get a handle on that measure up your radiation (zone by zone if multi-zoned.) With the heat load numbers and radiation numbers it's possible to ballpark how much of the time a condensing boiler would actually be delivering condensing efficiency, and how low the water temperature would be before the boiler could potentially short-cycle. The napkin math on that lives here.
If you can share the fuel use information I can run the load numbers here, if that's any easier.
https://www.greenbuildingadvisor.com/article/sizing-a-modulating-condensing-boiler
The ES2 series has not been discontinued, but there may have been recent changes/updates.
However the 89,000 BTU/hr DOE output of the ES2-4 is ridiculously oversized for most normal sized houses (even if you're also using it to heat domestic hot water), and not the best choice for 19 out of 20 houses in your ZIP code. Even the ES2-3 is more than 1.5x oversized for most homes in NYC (ASHRAE recommends 1.4x oversizing, not more.)
It needs a correctly sized flue liner to be vented into a masonry chimney, but it doesn't need to be stainless.
The ES2 is more expensive than several fire-tube modulating condensing boilers out there that would be a better size fit, even at a comparable higher BTU output, and cheaper to install too.
Take a BIG step back, gather up some wintertime-only oil fill up slips, and first run a fuel-use based load calculation using the oil burner as the measuring instrument to get a handle on your heat load at +15F outdoors (NYC's 99th percentile temperature bin aka "99% outside design temperature".) The largest cast iron boiler should have a DOE output no more than 1.4x the fuel-use calculated number, but not less than that number.
With a modulating boiler there is more flexibility, but the minimum modulated output becomes the more important number. To get a handle on that measure up your radiation (zone by zone if multi-zoned.) With the heat load numbers and radiation numbers it's possible to ballpark how much of the time a condensing boiler would actually be delivering condensing efficiency, and how low the water temperature would be before the boiler could potentially short-cycle. The napkin math on that lives here.
If you can share the fuel use information I can run the load numbers here, if that's any easier.
https://www.greenbuildingadvisor.com/article/sizing-a-modulating-condensing-boiler
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I will look at that but it is an older, larger home, 5 bedrooms 3 zones. Separate gas water heater. Currently has a Pacific oil burner/boiler which is over 60 years old
Most 50-100 year old homes with modest insulation & window updates come in at under 20 BTU/hr per square foot of conditioned space (not counting basements in that area number), many come in under 15 BTU/hr per square foot even approaching 10 BTU/ft^2 @ +15F when the foundation is insulated.
While heat load is not a function of the square feet of conditioned space, using those as rules of thumb for the likely heat load limits. Is your house over 5000 square feet? Over 4000 square feet?
Even a 60+ year old oil boiler can be a useful tool for placing an upper bound on the heat load using fuel use against heating degree-days. If the burner techs tested the raw combustion efficiency and wrote it on the tag use that as the correction factor rather than the name-plate efficiency numbers on the boiler itself. After 60 years the erosion/corrosion on both the water and fire side of the heat exchangers would be enough that even if it tested at 80% when new it's more likely to be in the 70% range now.
Run the fuel use numbers- the real loads are usually much lower than the contractor thinks they are.
If it turns out you really do need a ~100KBTU boiler, a Westinghouse WBRUNG100W or WBRUNG120W all stainless fire tube modulating condensing boiler is cheaper than an ES2-4, and have a 10:1 turn-down ratio making it easy to set them up to run at maximum condensing efficiency without short cycling. These boilers (and their HTP UFT-100W and UFT-120W exact equivalents) are very easy drop in replacements for cast iron, since they can almost always be pumped direct, no primary/secondary plumbing required, very little design changes need to be made to the system. The plastic venting for condensing boilers is also pretty cheap, and you may opt to side vent it and brick-up the chimney.
That particular series of boilers have a second set of ports and controls designed to support an indirect water heater, which would be more efficient (and faster recovering) than your gas fired standalone water heater. If the water heater is vented into the same chimney as the oil burner it's better to switch to an indirect when you swap the boiler, since the flue is crazy-oversized for just a water heater, and will have flue condensation/backdrafting risks. But if it's power-vented or you're willing to "wait and see" that decision/expense can be deferred.
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