Boiler replacement cost
Replacing a gas boiler costs $3,500 to $14,000, typically around $7,500. A standard efficiency unit on an existing system sits at the bottom; a condensing boiler needing new venting and a chimney liner sits at the top.
National average
$7,500
per project
On this page
- What it costs
- Standard or condensing
- Combi or not
- What a proper installation includes
- Frequently asked questions
- How long does a boiler last?
- Is my old boiler really that inefficient?
- Can I switch from a boiler to a furnace or heat pump?
- Do I need to replace the radiators too?
- Why is my new boiler noisier than the old one?
Replacing a gas boiler costs $3,500 to $14,000, typically around $7,500. A standard efficiency boiler on an existing system sits at the bottom of that; a condensing boiler that needs new venting and a new flue liner sits at the top.
A boiler heats water and circulates it through radiators or floor loops. It is a different job from a furnace, in a different part of the country, and it is worth knowing which you have before you start reading prices: if there is a large metal box blowing air into ducts, that is a furnace, and this is the wrong page.
What it costs
| System | Typical cost |
|---|---|
| Standard efficiency gas boiler, 80 to 86% AFUE | $3,500 to $7,000 |
| Condensing gas boiler, 90 to 95% AFUE | $6,000 to $11,500 |
| Combi boiler, heat and hot water in one | $6,500 to $14,000 |
| Oil-fired boiler | $6,000 to $12,000 |
| Electric boiler | $2,500 to $6,500 |
| Chimney liner, when a condensing boiler frees the flue | $1,200 to $3,500 |
| New PVC venting for a condensing boiler | $600 to $1,800 |
| Near-boiler piping, if being redone properly | $800 to $2,500 |
| Zone valve or circulator pump, each | $300 to $700 |
| Expansion tank | $250 to $600 |
| Removing an old oil tank | $500 to $3,000 |
The venting row is the one that surprises people. A condensing boiler does not vent up the old chimney, and if a water heater was sharing that flue, the chimney now needs lining for the water heater alone.
Standard or condensing
A condensing boiler pulls extra heat out of the exhaust by condensing the water vapour in it, which is where the efficiency comes from. It only does that when the water returning from the radiators is cool enough, below about 130°F.
That is the catch nobody mentions. A condensing boiler bolted to a system designed for 180°F water, with radiators sized for it, spends most of the winter not condensing and delivering closer to 87% than 95%. You paid for the higher number and are running at the lower one.
Condensing makes sense when:
- You have underfloor heating, which runs cool by design
- Your radiators are generously sized, or you are adding to them
- The installer will set up outdoor reset control, which lowers water temperature in mild weather
- Gas is expensive where you live and the payback maths works
Standard efficiency makes sense when the existing radiators are small, the budget is tight, and the chimney is in good order.
Combi or not
A combi boiler makes hot water on demand and does away with the cylinder, which frees a cupboard. It is common in Europe and increasingly sold in the United States.
It suits a small household with one bathroom. It struggles with two showers at once, because it is heating water in real time rather than drawing on a store. If your house has two bathrooms in regular simultaneous use, a system boiler with a cylinder is the better machine even though it takes more room.
What a proper installation includes
Boiler replacements are where corners get cut, because most of the work is invisible once the jacket goes on.
- The near-boiler piping redone to the manufacturer's diagram, not reused. The most common installation fault, and it causes short cycling and noise for the life of the boiler.
- A system flush before the new boiler goes in. Decades of sludge in old radiators will ruin a new heat exchanger.
- A new expansion tank and a checked pressure relief valve.
- Correct sizing, from a heat loss calculation rather than the output of the old boiler. Old boilers were routinely oversized by half.
- Outdoor reset control on a condensing boiler. Without it you are not getting the efficiency you bought.
- The permit, and an inspection.
Frequently asked questions
How long does a boiler last?
Fifteen to thirty years for a cast iron standard efficiency boiler, and fifteen to twenty for a condensing one. Cast iron boilers are famously long-lived; the controls and the circulators fail long before the block does.
Is my old boiler really that inefficient?
Probably less than you are told. A well-maintained 1990s boiler runs around 80%. Going to 95% saves about 16% of your heating gas, not half of it. The saving is real; the payback is usually eight to fifteen years, not three.
Can I switch from a boiler to a furnace or heat pump?
You can, and it means installing ductwork throughout the house, which is a substantial job in a finished home. The usual alternative is air-to-water heat pumps, which drive the existing radiators, or mini splits for cooling alongside the boiler for heating.
Do I need to replace the radiators too?
Not usually. They last generations. If you are going condensing and want the efficiency, you may want larger ones in the coldest rooms so the system can run at lower water temperatures.
Why is my new boiler noisier than the old one?
Most often near-boiler piping done wrong, air in the system, or a circulator pumping into the expansion tank connection rather than away from it. All three are installation faults and all three are the installer's to fix.
Read next
Furnace replacement cost$3,000 to $12,000per projectA gas furnace costs $3,000 to $6,200 at standard efficiency and $6,000 to $12,000 at high efficiency. The gap is wider than the equipment prices suggest, and the reason is venting.
Heat pump cost$5,000 to $13,000per projectA ducted heat pump costs $5,000 to $13,000 installed, typically near $8,000. The federal tax credit most guides still describe is, according to the IRS, no longer available.
Mini split cost$1,200 to $14,500per projectA single-zone ductless mini split costs $1,200 to $5,500 installed, typically $3,000. Price tracks the number of indoor heads far more than total capacity.
How long does an HVAC system last$6,500 to $22,000per projectA gas furnace lasts 15 to 25 years and an air conditioner 15 to 20. Those ranges are wide on purpose: two identical systems on the same street routinely differ by a decade, and almost none of it is brand.
How to pay for an HVAC system$6,500 to $22,000per projectAn $11,000 replacement usually arrives on the day the system stops, and that timing is what makes the financing expensive. Incentives first, then a home equity line, then a credit union. The spread across that list is thousands.