At some point in your life, you may find yourself standing in a utility room and wondering, “Just what am I looking at?” You might be touring a house or commercial building you’re interested in buying, or you might think it’s time for furnace repair or boiler service, but you aren’t sure what kind of unit is installed. If you aren’t an HVAC technician, you’ll need to know some clues to determine what’s heating the building: a boiler or a furnace.

Boiler and Furnace Visual Identification


  • Uses water; look for a circulator pump
  • Piping, usually copper, or PEX (plastic tube), no bigger than 1.25”
  • Older boilers may have a black iron pipe, called Schedule 40, or a mixture of that and copper pipe. In Category 4 condensing (high efficiency) boilers you won’t see a black iron pipe.

NTI FTV150 High-Efficiency Boiler


  • Uses forced air through ducts to heat; look for shiny, metallic ductwork
  • Main unit is larger and taller than a boiler
  • You won’t see copper use with a furnace, but if the house has an air conditioner, and you see ductwork, don’t be fooled by the insulated copper tubing you see in the utility room–it’s likely the line set for the A/C unit.

American Standard Twinned Furnaces

How Do Boilers Work?

When you think about a boiler, think about fluid mechanics. Wikipedia defines fluid mechanics as the branch of physics concerned with the mechanics of fluids (liquids, gases, and plasmas) and the forces on them.

With hydronic boilers, water is the vehicle that transfers the thermal energy to the radiator where it can then be distributed as heat. A hydronic boiler uses water in its liquid state. A steam boiler changes the water from a liquid state to a vapor state.

Here’s a great example of how water is an effective heat distributor: picture two balloons, one filled with water, and one with air. Put a lighter under the balloon with air, and the balloon will pop right away. But hold the lighter under the balloon with water and you’ll be able to hold it there for a good amount of time without the balloon popping. That’s because water is a great vehicle for pulling energy away from the surface of the balloon.

Boilers can move the water through a home in a variety of ways:
  • Through baseboards in the rooms
  • Inside the floor, called in-floor radiant heating
  • Heated driveway for snowmelt purposes

Note, typically radiant floor heat is installed during the construction of a new home. It can be retrofitted into an existing home, however, it’s a large and expensive undertaking to rip up floors and ceilings for installation.

Boiler Service Equals Boiler Safety

Boilers require more redundant safety than furnaces. Consider this: when water changes from a liquid state to a vapor state it expands to 1,000x times its original size. So, if one cubic foot of water turns to vapor all of a sudden, it will be 1,000 cubic feet of vapor. In a hydronic boiler, which uses liquid water only, you don’t want the water turning to vapor. That would mean the boiler has gone hydrostatic and it will cause an explosion. This is why regular boiler service is important in ensuring the unit is functioning properly.

To quote our certified technician, TJ: “With a hydronic boiler, ‘boiler’ is just a catchy name, we never actually want it to boil. We just want the water to get hot.”

A lot of boilers, especially older ones, don’t use induced draft motors so there’s no pressure switch to prove that the fluid is clear, or that the heat exchanger is clear. If there’s an issue with the rollout, carbon monoxide will burp out the front of the boiler is not maintained. With new, Category 4 condensing, or high-efficiency boilers, they have all the safety features embedded like the induced draft motor and the pressure switch, so there’s not an issue with the rollout. Either way, you want to keep up with consistent boiler repair service.

Schedule Boiler Service Repair

Boiler or Furnace: Which is Better?

The answer is it just depends on the use. It depends on whether the building is being built new, or if it’s an existing building, whether the building has or needs air conditioning and the age and floorplan of the building. In general, when it comes to replacement, if you have a boiler already, you will likely want to replace it with another boiler. The change can be made over to a furnace, but it’s quite a big job.

Pros of a Boiler:
  • Life expectancy is twice as long as a furnace when installed correctly
  • Boilers are highly efficient
  • Over time, boilers offer great cost savings on energy bills
  • Boilers are more powerful than a furnace because they are made for higher btu output
  • Boilers make it easier to zone the system. You can have a thermostat for different rooms, each controlling the temperature separately in that room.
  • A steam boiler is the most efficient way to heat a building, while a hydronic boiler is the second
Cons of a Boiler:
  • More expensive to install
  • Boiler service requires a much higher skill set in the technician
  • Less diverse, an air conditioner cannot be tied into a boiler. This is the reason you don’t see boilers as often in new builds; it’s not as cost-effective or easy to add an air conditioner separately.
Pros of a Furnace:
  • Considered ‘safer’ in general
  • More cost-effective to install
  • Very common, HVAC technicians are trained to work on them
  • Air conditioning units can be easily tied into a furnace
Cons of a Furnace:
  • Not as efficient because water (with a boiler) is just a vastly superior vehicle for energy
  • Takes more physical space with the ductwork throughout the house and into the rooms (this could be an issue with renovations or retrofitting)

Boiler Service and Furnace Repair

If it’s time for your boiler or furnace to be repaired or replaced, you can count on Simply Mechanical
and our NATE-certified technicians offer you the best models on the market.

We are an American Standard Customer Care Dealer and that is the primary brand of furnaces and air conditioners that we install. For boilers, we primarily install Dunkirk for cast iron boilers, and New York Thermal Institute (NTI) for high-efficiency, Category 4 boilers.

Learn more about boiler service or replacement

Learn more about furnace repair or replacement

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