Recommendations for a new oil boiler

My top choice would be an Energy Kinetics System 2000. Second would be a 3 pass boiler like a Buderus, Pure Pro Trio or Utica TriFire. If you are on a budget I would recommend a Peerless WBV, Weil McLain WGO or Crown pin type cast iron boiler.

Proper sizing and installation is the biggest factor that affects reliability and efficiency.

Check the chimney during the cold months. If you don't see a space between the condensate flume and top the flue you need a insulated lining…..

Another option for avoiding a liner is a direct vent boiler. That means a boiler that vents out the sidewall WITHOUT a power vent. The burner motor does it all. I have installed many of them over the years (have one myself) and I love them because you can get higher efficiency out of them without condensation/chimney liner worries. But like anything, they don't fit all applications. Some folks say they are not a good idea because when/if combustion is ever poor, then you get soot on house wall. That is the main reason I do not use "factory" wall hoods. So many of them have a dumb hood that allows the exhaust to rise up the wall instead of blowing it straight out as I like to do. But even with the many I put in with the dumb hoods (before I went to something better) it is rare to see any sort of discoloration on the wall.

Reminds me of the GAS boiler installers who vented a condensing boiler right where the homeowner parked his fancy car for the winter. The installing company ended up paying for the new, expensive paint job. So its not just oil combustion exhaust that needs to be handled correctly.

If your installer likes Weil-McClain, then that's the make to use. As has been said, make sure it is sized correctly — with hot water systems, to the heat loss of the house. The make of boiler is interesting, and they do differ — but they are all about the same efficiency fired on oil, and a happy and competent installer is much more important.

If you primarily heat with wood pellets, the ROI on a top of the line oil boiler vs. a basic cast iron boiler will be pretty long. proper sizing and installation is more important than picking WM vs. Peerless, etc.

If you do end up considering a direct vent unit, be mindful of where the exhaust exits the home vs. where you may spend time outside in the warmer months. I know a few people with direct vent oil boilers that complain of exhaust smells on the porch/deck if the wind is just right. I would stick with the chimney if you can.

The quality of the installation determines the reliability of the boiler. The installing contractor makes or breaks the job. I consider the Buderus to be a top of the line boiler, the only one I like better is the Energy Kinetics EK-1F. Check out the installation manual for details about the venting requirements. Make sure the installer follows the installation instructions, this is critical.

I don't recommend DIY maintenance, especially on a Buderus. Proper combustion analysis and draft measurements need to be taken annually. A combustion analyzer is an expensive, essential tool and learning how to interpret readings properly only comes from extensive training and experience, not YouTube videos. Leave it to professionals for the sake of you and your family.

Not all liners are insulated. I would guess that your liner is not insulated. In most cases involving an oil fired boiler, you do not need an insulated liner. You just don't want the condensation that forms in the chimney to damage the bricks or clay liner over time. Stainless steel can withstand condensation for many years. If the Chimney inspection did not show any corrosion of damage to the liner you have, then you are good to go with the Buderus.

I like Buderus over WM WGO boilers, because they are easy to maintain the heat exchanger with a large brush. The WM pin boilers are difficult to run that brush thru and many times you damage the combustion chamber when brushing the last section closest to the back of the boiler.

With any oil boiler, doing self maintenance is problematic, because most DIY folks lak the combustion analysis tools needed to get it right. I have had experience with doing proper maintenance on oil burners where removing a year's worth of lint and household dust from the burner fan, air intake and other air handling parts will end up needing no adjustment of the flame. But there are many burner men that neglect to make those cleaning steps and opt for making the air adjustment to get the combustion test numbers they are looking for.

I like to show my apprentice mechanics the best way to do oil burner maintenance is to get the burner as clean as possible so the original settings do not need to be adjusted.  Remove all the lint from the fan every year, remove the dust form the air adjustment opening every year, and check the pump pressure every nozzle change. Then you will find the original settings (if they were correctly made) will never need to be changed.

As long as you keep your maintenance to stuff that requires no combustion testing, like replacing the oil filter, and cleaning the burner fan each year, and brushing and vacuum cleaning the boiler heat exchanger if needed, then you will be good to go with DIY maintenance.  But when it comes to changing the nozzle and setting the proper air fuel mixture/pressure. Then you need to call the guy with the combustion analysis tools to get it right.  (unless you have an extra grand to purchase a set of gauges and tools to test for smoke spot, CO², O²,  stack temperature, and draft conditions)