The Way a Boiler Heats a House
A boiler burns oil or gas to heat water, and a circulator pump moves that water through copper baseboard, cast iron radiators or tubing under the floor. The water gives up its heat to the room and returns to the boiler to be heated again. Steam boilers, common in older houses on the North Shore and in parts of Nassau County, boil the water instead and let the steam rise to the radiators on its own.
Because it heats water, a boiler can do a second job: make the house's hot water, either through a tankless coil inside the boiler or by feeding an indirect water heater beside it. Many Long Island oil boilers do exactly that, which is why a boiler problem sometimes shows up first as a cold shower.
The Way a Furnace Heats a House
A furnace burns oil or gas inside a heat exchanger, and a blower pushes the house's air across the hot metal and out through ducts to registers in each room. The air returns through a grille, passes the filter and goes around again. Warm-air furnaces are more common in Long Island houses built from the 1960s on and in any house that was built with central air conditioning, since the two share the same ducts.
A furnace heats air only. A furnace house has a separate water heater, and the furnace filter has to be changed, because a clogged filter is the most common reason a furnace short cycles and the fastest way to wear out its heat exchanger.
Furnace vs Boiler: Comfort
Boiler heat is even and quiet. Baseboard and radiators warm the room steadily, nothing blows, and the air is not dried out. The trade-off is speed: a boiler takes longer to bring a cold house up to temperature, and you cannot add central air to it without a separate duct system.
Furnace heat is fast. Rooms warm within minutes of the burner firing, and the same ducts carry air conditioning in summer and can take a humidifier or an air cleaner. The trade-off is drier air in winter, some fan noise, and rooms at the far end of a duct run that never get quite as warm as the ones near the furnace.
Furnace vs Boiler: Running Cost
The number that decides running cost is the AFUE rating, which the U.S. Department of Energy defines as the ratio of useful heat delivered to the energy in the fuel over a whole heating season. A furnace and a boiler with the same AFUE burn about the same fuel for the same heat. What separates them in practice is age: a 1980s unit of either type is far less efficient than a modern one, and that gap is bigger than any gap between the two types.
Ductwork tilts it. Ducts lose heat, especially the ones that run through an unheated attic or crawl space, and a furnace pays that tax every cycle. A boiler loses almost nothing between the boiler and the baseboard. On the other side, a boiler that also makes hot water runs in summer too, which is efficient if the coil is clean and wasteful if it is limed up.
Furnace vs Boiler: Repairs and Service
Both are built around the same oil burner, so a tune-up is the same job on either: new nozzle, filter and strainer, a vacuum, adjustments and a safety test, $219 with Domino. The oil burner tune-up page lists every step.
Where they differ is in what fails. A boiler's trouble spots are the water side: circulators, zone valves, the expansion tank, the relief valve and, late in life, a cracked section. A furnace's trouble spots are the air side: the blower motor, belt, limit and fan controls and, late in life, a cracked heat exchanger.
The common parts of both ride on every truck, so most repairs on either type end on the first visit. The boiler repair and furnace repair pages go into each.
Which One Fits Which Long Island House
- A house with baseboard or radiators and no ducts has a boiler, and should keep one. Adding ducts to a finished house is a major job.
- A house with registers in the floor or ceiling has a furnace, and if it has central air, the furnace and the air handler share those ducts.
- A house with a tankless coil making its hot water has a boiler doing two jobs; replacing it with a furnace means adding a water heater too.
- A house with a damp basement near the water table is harder on both, and worth a look at where the unit sits before replacing it.
Does Switching From One to the Other Ever Pay?
Almost never. Going from a boiler to a furnace means building a duct system through a finished house; going the other way means running baseboard and piping to every room. The construction cost swamps any difference in running cost for decades. The exception is a gut renovation where the walls and ceilings are open anyway, and even then the choice usually follows whether the owner wants central air.
The spend that does pay is replacing an old unit with a modern one of the same type, correctly sized for the house as it is now, with new windows and insulation taken into account. Replacement estimates are free, you get the repair price next to the replacement price when a repair is on the table, and financing is available on new equipment. The boiler replacement and furnace replacement cost pages cover each.
Related Reading
- How long an oil burner and boiler last
- The best season to replace a heating system on Long Island
- Preparing for a heating system installation
Boiler or Furnace, Domino Services Both
Call (631) 867-2231 any time for a repair, a tune-up or a free replacement estimate. NORA-certified technicians work on oil and gas boilers and furnaces of every make across Suffolk County, Nassau County and Queens, with the price quoted before any work starts.
Source: U.S. Department of Energy, Federal Energy Management Program, "Purchasing Energy-Efficient Residential Furnaces," energy.gov.