--108.52.xxx.xxx

I would get bids for 2 gas furnaces, and ductwork and compare. I have had ductwork installed in ceiling of a small house….centrally located furnace and sheet metal plenum and flex duct to ceiling registers. --149.76.xxx.x

Depends on the type of gas boiler the contractors are going to use. High efficiency gas boilers cost more where a regular standard efficiency gas boiler will cost less. If the chimney requires lining the cost will higher where it is better to buy a gas boiler that vents directly through the wall. Slant Fin is the most reasonably priced gas boilers where regular, power vent and high efficiency. Another option is buy a wall mounted high efficiency gas boiler than vent directly through the wall for combustion and exhaust gas. Use Uponor A type heating pipe where can be a DIY option or have a plumber separate out two heating zones. Three items are venting chimney, piping, and boilers installation. Commercial pex piping is more cost effective as labour intensive for two heating zones. As long as the existing system is not steam where would have to buy copper finned radiation which is made by Slant Fin. Go into Slant Fin website along view videos about heating systems on You tube about heating systems. So ask more about what the contractors are installing than get break down and how separating two heating zones. If install one high efficiency gas boiler then can install Danfoss non electric thermostatic valve on radiators then limit the heat to room temperature then install Tekmar electronic boiler control in basement where keep temperature enough for heat but drop if tenant leaves window open along turning off heat on day and nights where no heat is required where will pay electronic control in one heating season or less. --216.110.xxx.xxx

I don't know anything about boilers--I agree that I'd explore the option of putting in gas furnaces. There are a lot more HVAC repair guys that can fix furnaces than can fix boilers! --104.230.xxx.xxx

price out furnaces as opposed to boilers, cheaper to run duct work etc then just replacing the boiler and in case of a freeze up you wont loose your heating system --38.248.xx.xx

What type of boiler heat? Is this a steam or a hydronic boiler system? I am a boiler HVAC mechanic with years of install and service experience. Others are advising you to throw the baby out with the bath water. I am saying not so fast. There are other options you can explore. --184.57.xxx.xx

There is no easy answer in this. If it were me, I would stay boiler systems but install a second one and split the loops. --67.140.xx.xxx

Oil has been expensive the last few years so all things being equal, I would choose gas over oil. It is also easier for tenants to manage payment wise as long that you have natural gas there. If you don't propane is still cheaper than oil --67.140.xx.xxx

The reason why a building requires a heating and cooling is heat loss and heat gain through the walls and ceilings where if insulation and windows were upgrade then the building would net zero where no heating or cooling system would be required. Spray foam in walls and ceilings is air tight where the heat transfer is reduced then the HVAC will operate for shorter periods of time which will last longer. Again a furnace is ok if furnace was installed first where a boiler can be changed in less than a day. While conversion is costly where may never recover money for a long period of time but when you sell property the values goes up along it is much easier to sell. A high efficiency gas boiler will use less natural gas as the secondary heat exchanger will extract heat that goes up chimney where can start off with a high efficiency gas boiler then later add another high efficiency gas boiler then split heating to two zones. Oil boilers require cleaning every year along with the oil is a up and down depending on world price. --216.110.xxx.xxx

Appreciate all the comments. Jim (OH), it's hydronic, not steam. The zones are already separated out, just all running off of one boiler. As for furnace vs boiler, it's an old three-story brick house built in 1888, with plaster and lathe on many of the inside exterior walls. I highlight that because I think retro-fitting for ductwork would be prohibitively expensive, so I'm sticking with the boilers, but maybe there's something I'm not thinking of. I re-lined the chimney with stainless steel about 20 years ago. Robin, good point about the monthly utility service fees (x2), even if you're not using it. That'll eat into the price advantage. At least with oil, there's no monthly bill if I'm not using it. --108.52.xxx.xxx

Appreciate all the comments. Jim (OH), it's hydronic, not steam. The zones are already separated out, just all running off of one boiler. As for furnace vs boiler, it's an old three-story brick house built in 1888, with plaster and lathe on many of the inside exterior walls. I highlight that because I think retro-fitting for ductwork would be prohibitively expensive, so I'm sticking with the boilers, but maybe there's something I'm not thinking of. I re-lined the chimney with stainless steel about 20 years ago. Robin, good point about the monthly utility service fees (x2), even if you're not using it. That'll eat into the price advantage. At least with oil, there's no monthly bill if I'm not using it. --108.52.xxx.xxx

With natural gas it is possible to get 95 per cent efficiency with a high efficiency gas boiler where in a period of one year the annual natural gas bill is a lot less than oil. With oil boilers limited to 87 per cent efficiency along annual cleaning every year. High efficiency gas boilers are low mass which require a primary and secondary heat loops where it recommend to install Spiro Vent air and dirt separate device to keep the black sludge and air out of the heating system. Expensive where install Uponor radiant floor heating where the heating temperatures are really low where the entire year the boiler operates at 95 per cent. If there are already two heating loops then it should cost as much. --216.110.xxx.xxx