Best Of

IMHO for an EG properly installed to fail in 10 years probably means one thing. Excessive MU water.

I would put a water meter on the boiler make up water and keep a sharp look out for small leaks they can add up.

Excessive MU water will eat a boiler and any returns below the water line very fast.

I went on a job the last year before I retired. One of the few times a boiler scared me. I have posted this before so maybe you have heard this story. If so sorry for the repeat.

But for me I will never forget this one. I think about it once in a while.

2,500000 btu Burnham gas boiler 15 psi steam. Customer said it was ok but the burner was noisy, I got to the job and began setting up my analyzer. Steam pressure was 10psi, normal it was a process job. I came out to the front of the boiler and the steam was 25 psi!!!

My first thought was "what the ——!! Then I thought bad gauge. Shut it down and got a gauge out of the truck. No the steam was 25 psi.

Safety valve corroded shut

Manual reset safety pigtail plugged

steam operating control pigtail plugged.

I often wonder what would have happened 20 min later if I wasn't there? What if I stopped for coffee? Would the boiler have gone through the roof like in the old days? Would people have been killed? Or would it have gotten to 50psi and the safety valve finally opened?

And the one that really bothers me. How could this boiler have operated all day with no issue maintaining 10 psi and modulating and I walk in the door and all of a sudden 3 things fail?

No, I think it went like this.

Safety valve corrodes shut.

Manual reset limit pigtail plugs up

I walk in the door and the operating control pig tail says I have had enough.

Steam boilers in MA get inspected every year,

I think I saved the insurance company a million dollars and their boiler inspector still has a job. I think I am lucky I wasn't 20 min later I may not be around.

This.

From a relatively educated homeowner's point of view, I would do the following:

• Definitely convert to natural gas if you can, as you have stated is your plan. This is for me a no-brainer regardless of the boiler or furnace technology you choose. Yank out those oil tanks before they fail and cause an environmental disaster in your basement.
• Keep the hot water radiators. Hot water radiant is a great heating technology. You will be able to re-use the existing piping to the radiators, or if any needs to be replaced, it can be done cheaply and simply with oxygen-barrier pex piping
• Avoid a "high efficiency" boiler. The higher up-front cost, greatly increased maintenance requirements, and shorter lifetime do not make up for the slightly higher efficiency
• Install a cast-iron atmospheric gas boiler. It is dead simple, everyone knows how to keep it running, it requires nearly no maintenance, and it will last for 30 years
• Get a new standalone water heater. Do not fall for suggestions that would use the boiler to heat your domestic hot water. These are complex and require a lot of up-front material and labor cost for no measurable gain, and they "tie" your hot water to your boiler so that if the boiler fails you also lose hot water. You can choose a natural gas one, or my advice is to strongly consider a heat pump water heater which will likely come with attractive incentives from the state and/or utility company
• Check your chimney, you may need a stainless steel liner but it should be an easy install for a chimney professional

Additional edit: You can make your AC unit be a heat pump for marginally more $$ and then you can use it for cost-efficient heating in the autumn and switch over to hot water boiler when it gets cold. This will give you a great backup as well.

I'm with @ethicalpaul — and basically your friend's father-in-law, except that like Paul I'd go with plain vanilla atmospherics rather than fancy condensing units.