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Furnace or Boiler? What the Basement Tells You Before You Buy

Writer: Bob Wiltse
Bob Wiltse
43 minutes ago
7 min read

How to size up the heating system on a Massachusetts home tour: age, efficiency, venting, and the service paper trail.


Bob Wiltse, REALTOR®

Research & Writing Assistant: Claude.ai

October 29, 2026


The heating system is one of the costliest parts of a house to replace. It affects your comfort, fuel bills, and safety, since anything that burns fuel can produce carbon monoxide. Five minutes in the basement can tell you a lot.


What to look for in a boiler vs. furnace


First, which one is it? A furnace heats air and pushes it through ducts. You’ll see floor or wall registers. A boiler heats water or makes steam and sends it through pipes to radiators or baseboards (DOE).


Furnace (L) or Boiler (R)? What the Basement Tells You Before You Buy
Furnace (L) or Boiler (R)? What the Basement Tells You Before You Buy

On a tour, look for:

  • The age. The unit’s data plate usually shows a model and serial number. The serial often encodes the year built. DOE estimates a typical life of 15 to 30 years for furnaces and boilers (DOE). Age alone isn’t a verdict. Care matters.

  • The efficiency rating (AFUE). AFUE means Annual Fuel Utilization Efficiency: how much fuel becomes heat. DOE groups old systems at 56–70%, mid-efficiency at 80–83%, and high-efficiency at 90–98.5% (DOE).

  • Service tags. A dated tag or sticker on the unit shows when it was last tuned up.

  • The vent. Older units vent up a chimney. Many high-efficiency units vent out a side wall through pipes. Look for solid pipes that are tightly joined and not warped or discolored (MA Board of Plumbers and Gas Fitters).

  • Clear space. State fire officials say to keep anything that can burn at least three feet away (DFS).

  • CO alarms. Massachusetts requires CO alarms in most homes (M.G.L. c. 148 § 26F½).


The products and what they do


  • Hot-water boiler (hydronic). Quiet, even heat through baseboards or radiators. Trade-off: no ducts, so central air requires its own system.

  • Steam boiler. One of the oldest heating systems, so you’ll mostly see it in older homes (DOE). Very durable radiators. Trade-off: needs a tech who knows steam and comfort depends on good balancing.

  • Forced-air furnace. Heats fast and shares ducts with central air. Trade-off: can feel dry and leaky ducts waste heat.

  • Condensing (high-efficiency) furnace or boiler. Pulls extra heat from the exhaust, reaching about 90–98% AFUE. Many are "direct vent" (sealed): they take outside air in one pipe and send exhaust out another to avoid backdrafting (DOE). Trade-off: more parts and a wall vent that must stay clear of snow.

  • ENERGY STAR levels. In the northern U.S., ENERGY STAR furnaces are 95% AFUE or higher (DOE FEMP). ENERGY STAR gas boilers are 90% or higher (DOE FEMP).


Questions to ask


Seller:

  1. How old is the system, and do you have service records?

  2. What did you spend on fuel last winter?

  3. Any rooms that stay cold?

Home inspector: 4. Is the vent or chimney in good shape for this appliance? 5. Any signs of leaks, rust, soot, or backdrafting?

Contractor (if you plan changes): 6. Was the last install permitted and inspected?


How old is the boiler or furnace?


The quickest way is the label on the unit itself. Here’s where to look, starting with the easiest:

  1. The rating plate (data plate). This is a metal or foil label on the unit. On a furnace, it’s usually behind the front access panel. On a boiler, it’s on the side or the jacket. Some plates print a manufacture date outright. Turn off power at the service switch before removing any panel.

  2. The serial number. Most manufacturers build the date into the serial number, often as the first four digits (year and week, or week and year). Every brand does it differently, so the surest way to decode it is to call the manufacturer’s customer support with the model and serial number. Many brands also explain their format on their website.

  3. The install sticker or service tags. Installers often leave a sticker with their name and the install date. Dated tune-up tags hanging on the unit help too, since the earliest tag gives you a rough floor.

  4. Your paperwork. Check old invoices, warranty registrations, and your home inspection report from when you bought the house. Inspectors usually estimate the age of heating equipment.

  5. Town permit records. In Massachusetts, a new heating system needs a permit. For gas, that’s the gas inspector. For oil, the fire department issues the oil burner permit. The building or fire department can often look up the permit by address, and that gives you the install date.

  6. Your fuel or service company. Oil dealers and HVAC companies that have serviced the house often have the install date or equipment details on file.


One thing to keep in mind: the serial number gives you the manufacture date, not the install date. The two are usually within a year of each other, but a permit or invoice will tell you exactly when it went in.


Red flags


  • Soot, rust streaks, or a scorched look near the burner

  • Warped, cracked, or loose vent pipes

  • Water on the floor or a dripping relief valve

  • No service tags and no records

  • Missing or old CO alarms near the heating system


If you're buying / If you're selling


Buying: Ask your inspector to look closely at the heating system and vent. If it’s old or the report flags it, request a heating tech’s evaluation during your inspection period.

Selling: Service it before listing and leave the dated tag on. Gather records, permits, and recent fuel bills.


The Massachusetts angle: codes, fuel rules, and Mass Save


  • Code: oil heat. Oil-heated 1–4 unit homes must have an oil safety valve or a sleeved oil supply line, installed by a licensed oil burner technician (MA fact sheet). Oil burner installations need a local fire department permit and inspection under 527 CMR (Topsfield FD example).

  • Code: gas heat. Venting for gas appliances must be done by or under a licensed plumber or gas fitter, with a permit and a final inspection (248 CMR policy).

  • Best practice: Have gas and oil systems professionally checked every year and keep vents clear of drifting snow (DFS).

  • Mass Save: The 2025–2027 plan stopped rebates for gas and oil furnaces and boilers, even efficient ones, and shifted incentives toward heat pumps (WBUR).

  • Energy code tiers. Under the Specialized Code, new mixed-fuel homes must be pre-wired for future all-electric use and usually add solar (DOER FAQ). As of June 2026, 60 towns had adopted it, including Lexington, Concord, and Arlington (mass.gov). Those three, plus Acton, Lincoln, Newton, and Cambridge, are in the state's Fossil Fuel Free pilot, which lets them require new buildings and major renovations to be fossil-fuel free (mass.gov).


Your town may have stricter rules. Cities and towns choose their energy code tier, and many have local bylaws, board of health regulations, zoning, and building and fire department policies beyond state code. Always check with your local building department, board of health, or fire department.


Bottom line


You don’t need to fix a boiler to judge one. Check the age, efficiency, vent, and records. A well-kept older system can last years.


FAQ


How do I tell if a house has a boiler or a furnace? Look at how heat enters the rooms. Floor or wall registers mean a furnace moving warm air through ducts. Radiators or baseboards mean a boiler sending hot water or steam through pipes. Some homes have both, such as a boiler for heat plus a separate air handler for central air.

What is a good AFUE rating? DOE calls 90% to 98.5% AFUE high efficiency, and 80% to 83% mid-efficiency. Older systems can be 56% to 70%. In the northern U.S., ENERGY STAR furnaces are 95% or higher, and ENERGY STAR gas boilers are 90% or higher. A higher number implies less fuel wasted.

How long does a boiler or furnace last? DOE gives a typical range of 15 to 30 years. Regular service helps a system last. Age alone doesn't mean a system is failing. Ask for records, look for dated service tags, and have your home inspector or a heating technician evaluate the system's condition before you buy.

Does Mass Save give rebates for a new gas or oil boiler? Not under the current plan. The 2025–2027 Mass Save plan stopped rebates for gas and oil furnaces and boilers, even high-efficiency ones, and shifted incentives toward heat pumps. Check Mass Save directly for the programs available when you're ready to replace a system.


What does Massachusetts require for oil heat? Oil-heated homes with one to four units must have an oil safety valve or a sleeved oil supply line, installed by a licensed oil burner technician. New oil burner installations need a permit and inspection from the local fire department. Your town's fire department can tell you its process.


Buying or selling a home in Massachusetts? I help buyers know what they're looking at and help sellers get their homes market-ready. Call or text me at 978-793-1719, email bob@bobwiltse.com, or visit bobwiltse.com.


Sources


Disclaimer: I'm not an HVAC contractor. This article is general information, not professional engineering, legal, health, or code-compliance advice. Codes change and vary by town. Consult licensed professionals and your local building department, board of health, or fire department before making decisions about your home.


Bob Wiltse is a REALTOR® with eXp Realty and a former licensed construction supervisor. Because where and how you live matters.

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