Best Of

I would keep the CI rads.

Not a mod con guy but with CI rads and starting from scratch you have the ability to condense and modulate. If I had an installer I could trust who could service it I would be tempted to go mod con.

That being said if I was in a remote location where service is difficult it would be a CI boiler.

2 boilers would be a good idea and give you some back up. You could pipe 1 boiler to each system and have a couple of "emergency cross over valves" if one boiler fails.

And if you decide to leave it as two units you could have 2 gas meters..

Lots of options.

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 wouldn't rule out Viessman, or any reputable, Gas fired, Wall-Hung Condensing boilers just yet. If you get the right installer/s, that has experience, and will be the ones servicing it, that option should be fully explored. We have excellent State-of-the-art Oil-fired equipment out there too. You need apples to apples comparisons to make such a decision.

Last, it can often be a rookie mistake to fall prey to the thinking that "one contractor can do it all" for you....that's its "just easier" to have one company handle the plumbing, heating and AC. Mad Dog

If the house will be used as a single home rather than a duplex with two units occupied separately, you might consider one larger boiler rather than two smaller ones. There could be significant savings in installation costs.

Every house I've ever seen that was converted to forced air was a train wreck. Furthermore, why would you want to remove a radiant heating system? The radiant is a premium system. Forced air is for the peasants. Radiators are works of art. Registers are holes in the ground for vermin to crawl in.

The heating system is part of the house. One does not swap an arm or a foot like they are articles of clothing. In the same way, the mechanicals are just as essential to a structure as any architectural detail might be.

I like the advice of your father's friend. That's probably what I would do without knowing all the details. Regarding boilers: there's merit in keeping it simple. But I do like the modulation that comes with the fancier "mod-con" equipment. The modulation makes zoning more practical. The modulation allows the burner to ramp up and down, instead of being just full on or off. I like that because the boiler runs closer to a state of equilibrium with the heat loss of the home.

Actually, you don't need conventional ducting if you use a high-velocity A/C system. These are great for A/C since they move the air more quickly which makes you feel cooler. But they don't do well for heating since they move the air more quickly which makes you feel cooler.

Radiators heat by radiation as well as convection. Think of the sun- when you're outside and a cloud blocks the sun, you feel cooler- that's radiation. No forced-air system can ever equal this. The increased comfort from radiators means you don't have to turn the thermostat up so far, which saves fuel. I don't know where @Kaos is located, but he must be in an area with a lot of salesmen who want to pad the bill by pulling radiators out, then cash in when they are scrapped.

@lchamb, the rads in my house will only be removed over my dead body. Keep yours.

And regarding boilers, the Burnham (not Buderus) MPO you have is a first-class unit. Burnham throws a temper tantrum when we talk about putting gas conversion burners in these, but it can be done with the right burner. I know of several that run well using the Carlin EZ-Gas Pro.

The Smith is older- I think it's a BB14 series- and though it's built like a tank, if you're looking for efficiency I'd replace it.

@lchamb An important thing to add. When you do make your choice on what to do, choose the installer as well as the product. A good relationship with a reputable company cannot be understated. Look again at the above @ethicalpaul and @Jamie Hall posts.