I read a fair number of posts related to heating system sizing. I always read the same info, every unit always seems to be 2 or 3 or more time the size it needs to be.
That I can accept, but what I don't understand is that there doesn't seems to be many appropriate sized heat units for the typical home and even less of a selection for a small home. The only units that seem to be capable of being properly sized are modulating condensing gas units. Even then the only ones that seem to be sized correctly would generally be the smallest size from just about any mfg.
Are there any oil fired boilers in the 40k BTU range?
Seems like a rant to me, and it is, but just trying to see if I am missing something.
There are physical limit to how small you can jet an oil burner and keep it clean, which puts the smallest oil boilers in the ~60KBTU range. SFAIK there has been no commercial release of burner technology that takes a different approach.
AFUE testing is done at 1.6x oversizing, so if your actual design condition heat load is < 35KBTU/hr even the smallest oil boilers out there won't quite hit their numbers. But how far it slips down the efficiency cliff varies. If it has the dumbest bang/bang controls it can be a fairly severe hit, but much of that can mitigated if smarter heat-purging controls (and buffering thermal mass) is incorporated. As a retrofit solution the
Intellicon 3250 HW+ is pretty good, but some of the newer oil boilers have their own smart controls (and better insulation) to better deal with the oversizing problem.
FWIW: In a L.I. location the better class ductless air source heat pumps (Fujitsu Halcyon, Daikin Quaternity, Mitsubishi H2i, etc.) can cost less than half as much to heat with than oil at current oil & electricity pricing, and in open floor plan homes a 1-2 ductless-head solution can work pretty well, most of the time. If your 3-4x oversized oil burner is still in decent shape, buying a ductless system and using the oil boiler as the Hail Mary backup heat is usually a better investment than the latest-greatest oil burner that's "only" 2x oversized, or a propane-fired mod-con.
The math sort of works this way: A right-sized ductless in a L.I. climate will run a seasonal average coefficient of performance of about 2.7-3.0, and a 3x oversized oil boiler rated 85% AFUE will run about 75% efficient.
At $4/gallon and 75% efficiency, you get (0.75 x 138,000=) 103,500 BTU of heat into the system for $4, or ~26000BTU/$
At 20 cents/kwh and a COP of 2.7, you get (2.7 x 3412= ) 9212 BTU directly into the rooms (no distribution losses, which you likely have with the oil boiler), for 20 cents, which is ~46,000 BTU/$.
You'd have to have Block Island type electricity pricing for a ductless to be more expensive than oil, and even if you bought the smartest-best oil boiler that actually delivered 87-88% efficiency in your actual system (not likely) the ductless would still beat it on operating costs hands-down.
And unlike oil boilers, it IS possible to right-size ductless systems for your actual heat load. Of the three vendors/series mentioned, all have a specified output at -15C (+5F), which is below your 99% outside design temp. And when a ductless is oversized by 25-30% it actually improves the efficiency slightly over what a perfectly-sized system would deliver (but not by enough to make intentionally oversizing worthwhile), since as fully modulating systems they get higher efficiency at part load than when running flat-out.
If oil, propane, and electricity are your only options, you really owe it to yourself to look at ductless heat pumps (mini-split or multi-split.)