Boiler replacement cost dataset

The federal minimums

From 10 CFR 430.32(e)(2), for boilers manufactured on and after January 15, 2021.

Read in the regulation on govinfo, retrieved 2026-08-23. Note that gas hot water is 84% while a warm-air gas furnace is 80% — different appliances, different rules. The same paragraph adds a design requirement in as many words: “Constant-burning pilot not permitted”.

What decides whether a condensing boiler condenses

A condensing boiler with each of the three emitter types behind it, on the same house.

Going condensing costs $2,667 more on the reference house — $11,976 against $9,309. ⚠️ A condensing boiler only condenses when the water returning to it is cold enough, roughly 55 °C or below. Radiant floors run cool by nature and condense nearly always. Fin-tube baseboard and cast-iron radiators were sized around water at roughly 80 °C, so behind those the boiler needs an outdoor reset curve to spend meaningful time below its condensing point. Without it you have bought a 95% appliance and are running an 87% one.

By house, climate and zones

⚠️ The boiler size comes from the same shared screening module the furnace page uses — deliberately, so two pages of this site cannot give two different sizes for the same house. It is a rule of thumb from floor area and climate, not a heat loss calculation, and it tends to come out larger than a real one. Each zone adds a circulator, a valve, a thermostat and two and a half hours of piping and purging.

Line items

76% of the reference total comes from estimated rather than official figures. Labour is billed at the BLS wage for plumbers and pipefitters rather than for HVAC mechanics, because a boiler is a plumbing job with a burner attached and in many states it is a different licence.

The reasoning behind each figure

Gas boiler, standard efficiencyestimated, ±34%

• Cast iron or steel sectional, priced per thousand BTU of input, so a 100,000 BTU/h boiler lands around $2,200 to $4,500 for the appliance alone.
• A boiler costs several times what a warm-air furnace of the same output costs, and that is not a markup: it is a pressure vessel full of water with a heat exchanger built to last decades rather than a sheet-metal box with a burner in it.

Boiler, condensingestimated, ±31%

• Stainless or aluminium heat exchanger, modulating burner, sealed combustion. Roughly 60% more per thousand BTU than the standard unit.
• ⚠️ Whether you get the efficiency you are paying for depends on your emitters and on whether the installer sets up an outdoor reset curve. A condensing boiler running at a fixed 80 °C is an expensive standard boiler.

Oil boiler, standard efficiencyestimated, ±35%

• Around a quarter more per thousand BTU than the gas equivalent. An oil boiler carries a pressure-atomising burner assembly with its own motor, pump and ignition transformer, where a gas boiler has a burner tray.
• Its federal floor is also the highest of the four types, 86% AFUE, which is part of why the appliance costs more.

Burner set-up: nozzle, pump, filter and fuel lineestimated, ±45%

• Oil does not arrive ready to burn. The nozzle has to match the boiler, the pump pressure has to be set, and there is a filter and a fuel line back to the tank that a gas appliance simply does not have.
• ⚠️ This is also an annual service item rather than a fit-and-forget one. An oil boiler that is not cleaned and re-nozzled every year loses efficiency quickly and eventually stops. That running cost is real and it is not in this figure.

Setting and testing the oil burner

• Two and a half hours to set pump pressure, air band and draught, and then prove it with a combustion analyser. On oil this is not a formality: a badly set burner sooteds the heat exchanger within a season.

Electric boilerestimated, ±40%

• By far the cheapest to buy: a tank, a set of elements and a control, with no burner, no heat exchanger and no flue.
• The whole cost is what comes afterwards. Resistance heat costs three to four times what a heat pump costs to make the same heat, so the saving at purchase is repaid to the utility with interest.

Near-boiler piping and manifoldestimated, ±45%

• The tangle of copper or steel immediately above the boiler that everything else connects to. Fabricated on site, every time, and never the same twice.
• This is the part of a boiler job that separates good work from bad, and the part a homeowner cannot judge by looking. On a steam boiler it is not cosmetic at all: pipe it wrong and the boiler carries water over into the mains and hammers.

Expansion tank, air separator and fill valveestimated, ±46%

• Water expands when it is heated and has to have somewhere to go; air has to have somewhere to leave. These three small components are what stop a closed loop from either bursting a relief valve or gurgling all winter.
• Replaced with the boiler as a matter of course. An expansion tank that has lost its charge is the commonest cause of a relief valve that keeps weeping.

Low-water cutoff, gauge glass and steam controlsestimated, ±44%

• Steam-specific and not optional: a steam boiler fired without water in it destroys itself in minutes, so the cutoff is the control that matters most on the whole appliance.
• Also the sight glass and the pressuretrol. Steam runs at ounces of pressure, not pounds, and a boiler running at the pressure most people assume is a boiler wasting fuel and banging.

Circulator pumpsestimated, ±45%

• One per zone on a pumped system. Band separates a fixed-speed cast-iron circulator from a variable-speed one that costs a fraction as much to run — and a circulator runs for thousands of hours a year, so that difference is not trivial.
• Steam does not use them: steam moves itself.

Zone valves, manifold and controlsestimated, ±44%

• One per zone, plus the relay that lets the thermostats call the boiler independently.
• Zoning is the quiet advantage of hot water over warm air: heating two rooms and not the other six is trivial here and awkward with ducts.

Outdoor reset control and high-volume circulatorestimated, ±45%

• What makes a condensing boiler behind old radiators actually condense: a sensor outside, a curve that lowers the water temperature as the weather mildens, and a circulator matched to moving a lot of water at low resistance.
• ⚠️ Without this the boiler runs at a fixed high temperature, never condenses, and delivers roughly the efficiency of a standard unit that cost a third less. It is the single most skipped item on a condensing boiler installation.

Extra fill, purge and bleed time for cast-iron radiators

• Two and a half hours more than a baseboard system, and it is not padding: cast-iron radiators hold several times the water volume of fin-tube baseboard, so filling the system, purging every zone and then bleeding each radiator individually simply takes longer.
• It is also the step that gets rushed, and the symptom is a radiator that stays cold in a system where everything else works.

Mixing valve and radiant manifoldestimated, ±47%

• Underfloor radiant runs far cooler than a boiler makes water, so a mixing valve blends the return back in to hold the floor temperature down, and a manifold splits the loops.
• It is also why radiant and condensing boilers suit each other: the low return temperature that radiant needs is exactly the condition under which the boiler reaches its rated efficiency.

Indirect hot water tankestimated, ±42%

• A storage tank with no burner of its own, heated by a zone off the boiler and insulated well enough to hold temperature for a long time.
• Fitted at the same visit because the piping is already open, which is most of why it is worth doing then rather than later.

Lining the chimney for the new boilerestimated, ±44%

• A modern boiler sends less waste heat up the flue than the one it replaces, so the same masonry chimney is now oversized for it. Oversized flues do not draw: the exhaust cools, condenses inside the brickwork and destroys it from within.
• A correctly sized stainless liner is the fix, and on a standard-efficiency replacement it is close to routine rather than optional.

Sealed plastic intake and exhaustestimated, ±45%

• A condensing boiler takes combustion air from outside and pushes exhaust back out, both in sealed plastic through a wall. It never touches the chimney.
• ⚠️ Which means the chimney is left behind — and if the water heater was sharing it, that flue is now far too big for the water heater alone. That is a separate line and it is the one people find on the invoice.

Condensate drain and neutraliserestimated, ±50%

• A condensing boiler makes several litres of mildly acidic water a day in cold weather. The neutraliser is a canister of limestone chips in the drain line: cheap, frequently skipped, and skipping it is what eats a cast iron waste stack from the inside.

Gas connection, shutoff and sediment trapestimated, ±44%

• Rigid pipe, a shutoff within reach and a sediment trap. Boilers are usually piped rigid rather than with a flexible connector, which is a little more work and a lot more durable.

Removal, setting and piping

• Twenty-four trade hours on a straightforward hot-water replacement, and more on steam. Getting the old boiler out is a job in itself: a cast iron sectional weighs several hundred kilos and frequently has to be broken up where it stands.
• A boiler is a plumbing job with a burner attached, which is why it is priced at the pipefitter wage rather than the HVAC one. Different trade, different licence in many states.
• The wage is official and regional; the hours are our estimate. There is no public productivity data for residential trades.

Piping and wiring each zone

• Two and a half hours per zone: pipe it, valve it, wire the thermostat back to the relay and purge the air out of it.
• Purging is the step that gets rushed, and an unpurged zone is a radiator that stays cold while everything else works.

Boiler circuit, service switch and controls wiringestimated, ±46%

• A fuel-burning boiler draws very little — pumps and a control board. An electric one is a different matter entirely and is excluded, because it needs a feeder rather than a circuit.

Electrical connection

• Two and a half hours for the circuit, the service switch beside the boiler and the low-voltage control wiring back to the thermostats.

Fill, purge, combustion analysis and balancing

• Four hours: fill the system, purge every zone, fire it, put an analyser on the flue, set the gas pressure and set the reset curve if there is one.
• On a condensing boiler this is where the efficiency is decided. A boiler commissioned at a fixed high water temperature will never condense, whatever it says on the box.

Breaking up and removing the old boilerestimated, ±45%

• Cast iron is heavy and old boilers are usually in basements with narrow stairs, so many are cut or broken into sections to get them out. Partly offset by scrap value, because cast iron is worth something.

Mechanical permit and inspectionestimated, ±55%

• Fees are set by each jurisdiction with no national schedule, hence a band. The inspection is also the only independent check that the flue, the gas connection and the relief valve discharge were done correctly on an appliance that holds hot water under pressure.

Not included in this dataset

Replacing radiators, baseboard or adding underfloor loops

This prices the boiler and the piping around it, not the emitters. Changing what heats the rooms is a much larger job and is what makes a low-temperature system possible in an old house.

Oil tanks

Above-ground or buried, they have their own price, their own lifespan and, if buried, their own environmental liability. None of it is modelled here.

Electrical service or panel work

The electric boiler option assumes a suitable feeder already exists, which for a whole-house electric boiler is a strong assumption. When it does not, that is a separate job on our electrical panel page.

Asbestos on old pipe insulation

Very common on boiler piping in houses from before the eighties, and much more likely here than on a warm-air system. It is tested rather than disturbed, and abatement is licensed work with its own pricing.

Buried or inaccessible pipework

Loops under a slab or behind finished walls cannot be assessed from the inputs this calculator asks for, and replacing them is a different order of job.

Warm-air heating

If your house has ducts and vents rather than radiators, you do not have a boiler. That is priced on our furnace page.