Boiler installation: what to know

What the job involves, what changes the price, and what to ask a pro.

What boiler installation is

Boiler installation removes an old boiler and sets a new one, with correct sizing, venting, gas or oil connections, controls and piping. The installer then tests the system and adjusts the heating zones so every room heats evenly.

Signs you need it

  • The old boiler is cracked, leaking from the heat exchanger, or repeatedly failing.
  • The boiler is old enough that replacement parts are hard to find.
  • Some zones heat unevenly and balancing the valves no longer solves the problem.
  • The gas or oil bills rise while the heat output falls.
  • You are adding a boiler to a remodel, an addition or a new zone.
  • The old boiler has no reliable venting, or it vents through a chimney that is no longer suitable.

What the pro does

  • Calculate the heat loss of the home and check the radiators or baseboards to size the new boiler.
  • Shut off and drain the old system, disconnect the gas or oil supply, and remove the old boiler.
  • Set the new boiler, pipe the supply and return, install the expansion tank, the circulator, the pressure relief valve and the low water cutoff.
  • Install the venting, which for condensing boilers often uses plastic pipe, and make the gas or oil and electrical connections.
  • Set the controls, the zone valves or relays, and any outdoor reset control, then fill and purge the system of air.
  • Test the combustion, the pressure, the safety shutoffs and each zone, then walk the homeowner through the controls.

What changes the price

Every job is different, so we do not publish prices. These are the things that move the quote up or down.

  • Boiler type and fuel, such as gas, oil or electric, and whether it is condensing or non-condensing.
  • Heat loss of the home, which sets the boiler output needed.
  • Radiator or baseboard condition, and whether any emitters must be added or replaced.
  • Venting route and materials, including whether a chimney liner or a new vent pipe is needed.
  • Piping changes, such as re-piping the system or adding zones.
  • Gas line or oil tank work and electrical service changes needed for the new boiler.
  • Controls, such as zone valves, outdoor reset controls or smart thermostats.

What a written quote should spell out

  • The model and output of the new boiler, with the heat loss calculation it is based on.
  • Removal and disposal of the old boiler and any oil tank or fuel line removal.
  • Piping work, the expansion tank, the circulator, the pressure relief valve and the low water cutoff, listed separately.
  • Venting materials and the connection method for gas or oil.
  • Controls and zoning, listed by item.
  • Start-up readings, combustion results and warranty terms.

Questions to ask before you hire

  • How did you calculate the heat loss, and does the boiler output match it?
  • Will you install a low water cutoff and a pressure relief valve, and show me where they sit?
  • What venting will the new boiler use, and does it fit the existing chimney or wall?
  • Will you test the combustion and each zone at start-up, and give me the readings?
  • Who pulls the permit, and will the gas or oil connections be inspected?
  • Will you purge the air from the whole system and balance the zones?
  • Who handles a warranty claim on the boiler and on the installation?

Red flags

  • The pro sizes the boiler by copying the old one without a heat loss calculation.
  • The pro wants to leave out the low water cutoff or the pressure relief valve.
  • The pro cannot explain the venting or where the condensate will drain on a condensing boiler.
  • The quote leaves out the purge, the zone balancing or the start-up test.

What you can do yourself

Clear the boiler room, move stored items, and make sure the installer can reach the old boiler, the piping and the venting route. Keep the model and serial numbers of the old equipment and keep the warranty paperwork. Gas, oil, venting, electrical connections and the purge belong to a licensed technician.

Licenses and permits

Boiler installation is commonly done under a contractor license, and it often requires a permit with an inspection for gas, oil and venting work. Check with your state or local licensing agency for the rules that apply to your installation.

Boiler installation questions

Why does a new boiler need a low water cutoff?

The low water cutoff shuts the burner off if the water level or flow drops too low, which protects the boiler from damage. A good installer will show you where it sits and how to test it.

Should I replace the radiators when I replace the boiler?

Not always. Radiators that are clean and sized for the house can stay. Ask the installer to check them, since a new boiler does not fix undersized or blocked emitters.

Can I keep my old pipes?

Sometimes. Pipes that are corroded, sludged or undersized can slow the new system. Ask the installer to inspect the piping and say what it recommends.

How do I know the boiler is set up right?

Ask for a start-up report with combustion results, system pressure and each zone's temperature. A good installer walks you through the controls and the pressure check.

About this guide

This national guide is written and checked by infinibell. Rules and conditions differ by place, so local pros are credited on guides for the cities they serve, not on national ones.

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