What Is a Boiler? Hydronic Heating Explained for NH

A boiler is a heating appliance that heats water and distributes it through pipes to baseboards, radiators, or radiant floor tubing. It is the heart of a hydronic heating system, a familiar setup in many older New Hampshire homes. Despite the name, a residential hot-water boiler does not normally boil the water. Operating temperature depends on the boiler, controls, outdoor conditions, and the baseboards, radiators, or radiant tubing it serves.

At A.J. LeBlanc Heating, we install and service residential boilers across Manchester, Bedford, Concord, Nashua, Salem, and Auburn.

Warranty requirements come from the written warranty terms for the selected boiler.

How a forced hot water boiler works

A typical residential boiler operates in a closed loop:

1. A burner (gas, propane, or oil) heats a metal heat exchanger.
2. Water flowing through the heat exchanger picks up heat.
3. An electric circulator pump moves the heated water through supply piping to the home's emitters (baseboards, radiators, or radiant tubing).
4. The water transfers heat to the room and returns to the boiler via the return piping.
5. The cycle repeats.

An expansion tank, pressure relief valve, air separator, and combustion controls round out the basic system.

Types of boilers used in NH homes

Cast-iron sectional boilers

Traditional cast-iron boilers can remain in service for decades when the equipment and system water are kept in good condition. Rated efficiency, condition, controls, venting, and the home's load all matter when evaluating one.

Condensing modulating boilers

Modern wall-mounted units can achieve high rated efficiency by extracting additional heat from flue gases. Condensing boilers have different maintenance and water-quality requirements, and their performance depends on system temperatures, controls, installation, and maintenance.

Combi (combination) boilers

A single unit that provides both space heat and on-demand domestic hot water. Common in smaller homes and condos where mechanical room space is limited.

Oil-fired boilers

Still common in rural and central NH where natural gas is not available. Modern oil boilers reach 87 to 90 percent AFUE. Cast-iron sectional designs from manufacturers like Burnham and Buderus are widely installed, along with low-mass welded steel designs like the Energy Kinetics System 2000.

What hydronic distribution looks like in NH homes

The boiler is just the heat source. The water it heats is then distributed through one of several emitter types:

• Fin-tube baseboard: the most common in NH homes built after the 1950s. Inexpensive, easy to install, requires hotter water temperatures.
• Cast-iron radiators: common in homes built before the 1950s. Hold heat well, comfortable on a cold morning, can operate at lower temperatures.
• Radiant floor tubing: tubing embedded in concrete slabs or attached under floor joists. Very comfortable, operates at low temperatures, ideal pairing with condensing boilers.
• Hydro-air handlers: a coil of hot water tubing inside an air handler, used to heat air for forced-air distribution. Combines hydronic heat source with ducted distribution.

Why hydronic heat is popular in NH

NH homes lean toward hydronic for several reasons:

• Older housing stock built with hydronic distribution from the start
• Quiet, even heat without the air movement of forced-air systems
• Easy room-by-room zoning
• Long equipment life (especially cast-iron boilers)
• Works well with traditional emitters and radiant floors

Boiler service and maintenance

Regular boiler service helps confirm safe combustion, reliable controls, proper system pressure, and clean heat-transfer surfaces. Follow the maintenance schedule and documentation requirements for the exact boiler and warranty.

Schedule boiler service or replacement

If you have a boiler that has not been serviced in over a year, or you are considering a replacement for an aging cast-iron system, contact A.J. LeBlanc Heating or call 603-623-0412. Serving New Hampshire families since 1928.

Frequently Asked Questions

Is a boiler the same as a furnace?

No. A boiler heats water and distributes it through pipes. A furnace heats air and distributes it through ducts. Different fluid, different distribution, different equipment.

Does a boiler actually boil water?

Most residential hot-water boilers do not boil the water. Operating temperature depends on the equipment, controls, outdoor conditions, and distribution system.

How long does a boiler last?

Cast-iron boilers can remain in service for decades when the equipment and system water are kept in good condition. Condensing boilers offer higher rated efficiency but have different maintenance and water-quality requirements. Age alone does not decide replacement. We also look at condition, repair history, venting, controls, efficiency, and whether the boiler still fits the home's heating load.

Can a boiler provide both heat and hot water?

Yes. A boiler paired with an indirect water heater uses the boiler to heat domestic hot water in addition to space heat. A combi boiler does both in a single wall-mounted unit.

How often should I have my boiler serviced?

Annually, ideally in late summer or early fall. For oil-fired boilers, annual service is essentially required to maintain clean combustion.