One calculator route, two boiler project models
A residential hydronic boiler replacement in USD and square feet. Natural gas, propane, oil, or electric equipment; standard, high-efficiency, or condensing/high-specification tier; like-for-like through complex conversion; reusable through significantly modified piping; removal, permit, controls, circulator, expansion tank, and vent/flue choices.
A broader boiler installation and boiler-based heating upgrade in GBP and square metres. New installation, combi conversion, system-boiler installation, relocation plus upgrade, or major heating-system upgrade; gas combi, system, conventional/heat-only, electric, or oil boiler; scale, smart controls, magnetic filter, power flush, radiators, cylinder, and gas/pipework choices.
For a normal UK like-for-like boiler replacement, the live Furnace Replacement route's UK boiler mode remains the simpler calculator. This Boiler route deliberately covers broader conversion, relocation, first-installation, and upgrade work.
How HomeCostNest builds the range
In the US model, fuel supplies the installed boiler allowance while home area adds a modest capacity-related component. Specification adjusts the subtotal; installation, distribution changes, removal, permit, controls, pump, expansion tank, and venting remain explicit.
In the UK model, project type supplies the main upgrade-oriented allowance. Boiler type and system scale adjust it, while controls, filter, flushing, radiator, cylinder, and gas or pipework choices remain visible additions.
Boiler capacity requires heat-loss and system assessment
Floor area alone omits climate, design temperature, insulation, air leakage, glazing, occupancy, emitter output, distribution temperatures, pipework, controls, zoning, domestic hot-water load where served, and system response.
An oversized boiler is not a substitute for assessment. Ask for the design heat loss, proposed output and modulation where relevant, distribution temperatures, emitter checks, hot-water assumptions, and commissioning requirements.
Boiler type describes system architecture
| Market | Choices | Project implications |
|---|---|---|
| US | Natural gas, propane, oil, or electric hydronic boiler | Fuel/electrical service, hot-water or steam/hydronic compatibility, piping, pumps, expansion, controls, venting or flue, condensate, and permits vary |
| UK | Gas combi, system, conventional/heat-only, electric, or oil boiler | Hot-water cylinder or tanks, pipework, pumps, controls, flue, condensate, fuel supply, radiator system, and conversion scope differ |
The US model should not inherit UK combi assumptions, and the UK model should not be described as a forced-air furnace. A boiler heats water for hydronic distribution; a furnace heats and distributes air.
Like-for-like replacement and system change are different budgets
A compatible like-for-like replacement can still require controls, venting, condensate, electrical, pump, expansion, piping, permit, removal, and commissioning work. A fuel, boiler-type, location, or distribution change can expand the project substantially.
The UK project choices explicitly include combi conversion, system-boiler installation, relocation, and major heating-system upgrade. A conversion can add or remove cylinder and storage components, change pipe routes and controls, affect gas or oil supply, and require building restoration.
Pipework, pumps, emitters, and water condition
The US calculator distinguishes reusable, moderately changed, and significantly changed distribution, plus circulator and expansion-tank work. Complete radiator replacement is not assumed.
The UK calculator exposes magnetic filtration, power flushing, additional radiator work, and gas or pipework modifications. These selections do not replace professional investigation of leaks, corrosion, contamination, balancing, water treatment, emitter output, or pipe sizing.
Domestic hot water changes UK system scope
A combi produces domestic hot water without a separate stored-hot-water cylinder, while system and conventional arrangements can involve cylinders and, depending on architecture, additional tanks or controls. Household demand, simultaneous outlets, pressure and flow, space, and retained components influence suitability.
The UK calculator includes hot-water-cylinder work only when selected. Water Heater Replacement content owns cylinder replacement budgeting; this boiler pillar covers cylinder implications only as part of the defined boiler-system project.
Efficiency ratings are not operating-cost guarantees
US fuel-fired boilers may use AFUE, a standardized measure of annual fuel-to-space-heat performance under its test method. UK boiler and seasonal metrics operate under their applicable standards and should not be treated as identical to AFUE.
Actual fuel or electricity cost depends on building heat loss, weather, rates, distribution temperatures, emitters, controls, cycling and modulation, installation, maintenance, hot-water use where applicable, and household settings. No bill saving, payback, ROI, or emissions result is promised.
Installation, access, controls, and closeout
| Scope | Items to clarify |
|---|---|
| Site and removal | Protection, access, lifting, disconnection, old-boiler disposal, hazardous-material exclusions, and making good |
| Services | Fuel or electrical supply, pipework, pumps, expansion, controls, vent/flue, combustion air, condensate, drainage, and water treatment |
| Distribution | Hydronic compatibility, temperatures, radiators or emitters, valves, balancing, flushing, filter, and excluded complete replacement |
| Compliance | Permit or notification, inspections, competent persons, testing, commissioning, documentation, and registrations |
| Handover | Operating instructions, settings, maintenance, warranty, service access, and retained-component responsibilities |
Gas, oil, combustion, electricity, hot water, and pressure
CPSC identifies fuel-burning heating equipment as a potential carbon-monoxide source. GOV.UK Approved Document J addresses combustion air, discharge of combustion products, and building protection in England. HSE requires domestic gas work in Great Britain to be performed by a Gas Safe registered engineer competent for that work.
Overlooked boiler-project costs
- Heat-loss assessment, hot-water assessment, and system design
- Fuel, electrical, vent/flue, combustion-air, condensate, and drainage changes
- Pumps, expansion, controls, filtration, flushing, water treatment, and commissioning
- Pipework, radiators or emitters, cylinders, tanks, valves, and distribution temperatures
- Access, relocation, lifting, cupboards, roof or wall work, and making good
- Removal, disposal, permits or notification, inspection, documentation, and temporary heating
Protect the repair-versus-replacement decision
This pillar assumes a replacement, installation, conversion, relocation, or upgrade project is being budgeted. It does not diagnose an existing boiler, interpret symptoms, estimate remaining life, or determine whether repair is financially preferable.
Those questions belong to the future Repair or Replace a Boiler specialist and a qualified professional assessment. Furnace content remains forced-air heating in the US; Heat Pump content covers a different technology; broader HVAC content owns combined or whole-system replacement.
Prepare comparable boiler quotations
- Obtain heat-loss and, where relevant, domestic-hot-water assessment.
- Choose the native US hydronic or UK boiler-system project model.
- Define fuel, boiler type, location, distribution, cylinder, controls, and services.
- Identify removal, access, permits or notification, safety, testing, commissioning, and making good.
- Separate optional upgrades from required compatibility work.
- Compare complete installed scope, rated performance, warranty, service support, exclusions, and documentation.
Plan with the right calculator
Enter your project details and select the United States or United Kingdom market for Low, Typical, and High planning estimates.
Frequently asked questions
Can property area determine boiler size?+
No. Area is cost-planning context only. Boiler selection requires a project-specific heat-loss assessment and consideration of distribution temperatures, emitters, hot-water demand, controls, fuel, and system design.
What is the difference between the US and UK boiler calculators?+
The US model estimates a residential hydronic boiler by fuel, specification, installation, and piping. The UK model is broader and covers new installation, combi conversion, system-boiler work, relocation, or a major boiler-based heating upgrade.
Is a system conversion the same as like-for-like replacement?+
No. Conversion can change pipework, pumps, controls, hot-water storage, flue or venting, condensate, fuel or electrical services, distribution, commissioning, and building work.
Is hot-water-cylinder work included?+
The UK calculator includes a separate cylinder-work option. It should be selected only when the proposed system requires that scope. The US calculator does not model domestic hot-water storage as a standard boiler addition.
Does the estimate include complete radiator replacement?+
No. The US model assumes reusable hydronic distribution unless piping changes are selected. The UK model includes an additional radiator-work allowance, not automatic complete distribution replacement.
Does this guide decide whether repair or replacement is better?+
No. It budgets a defined replacement or upgrade project. Diagnosis, condition, repair history, remaining-service uncertainty, and the repair-versus-replacement decision belong to a separate future specialist guide and professional assessment.
Sources & references
- Purchasing Energy-Efficient Boilers · U.S. Department of Energy
- Boilers · ENERGY STAR
- Carbon Monoxide Fact Sheet · U.S. Consumer Product Safety Commission
- Combustion Appliances and Fuel Storage Systems: Approved Document J · GOV.UK
- Domestic Gas: Frequently Asked Questions · Health and Safety Executive
- Boiler Installation and Replacement Cost · Angi
- Boiler Installation Cost Calculator · Checkatrade