Last reviewed: August 2026 · By the HVAC Brief Editorial Team · Our sourcing and editorial standards
Steam and hot water systems, the boiler-and-radiator or baseboard family, are the main heating equipment in 6.51 million US homes, about 5.3% of the housing stock. They are concentrated in older housing in the Northeast and Midwest.
They work differently from forced air: a boiler heats water or makes steam, which circulates to radiators or baseboard units that heat rooms by radiation and convection. There is no ductwork and no blower, which is why these homes usually have no central air conditioning path.
How common they are
| Main heating equipment | Homes (million) | Share of stock |
|---|---|---|
| Natural gas central warm-air furnace | 53.26 | 43.1% |
| Heat pump | 16.13 | 13.1% |
| Electric central warm-air furnace | 13.82 | 11.2% |
| Steam or hot water system | 6.51 | 5.3% |
Forced air dominates nationally, but that national picture hides regional concentration. Steam and hot water systems persist where the housing stock predates forced air, which is why a contractor in New England sees them constantly and one in Arizona almost never.
How the system works
- The boiler heats water, or boils it to steam, using gas, oil, propane or electricity.
- Distribution carries hot water through pipes by circulator pump, or lets steam rise through pipes by pressure.
- Emitters, cast iron radiators, baseboard convectors or radiant floor loops, transfer heat into rooms.
- Return brings cooled water or condensed steam back to the boiler.
Because heat moves through water rather than air, these systems respond more slowly than forced air and hold temperature more steadily. They also cannot deliver cooling, filtration or ventilation, which is the practical trade-off.
A house with hydronic heat has no ductwork to reuse, so adding central air means installing a duct system from scratch. That is the single largest reason ductless mini splits are common in this housing stock. See how mini splits work.
Fuel matters more here
Boiler systems are disproportionately oil-fired in the Northeast, which ties running cost to a volatile fuel. Residential heating oil averaged $4.01 a gallon in the 2025/26 season. Our heating oil price index tracks the weekly series.
Frequently asked questions
How many US homes use boiler or baseboard heating?
Steam and hot water systems are the main heating equipment in 6.51 million US homes, about 5.3% of 123.53 million housing units, per EIA RECS 2020. They are concentrated in older housing in the Northeast and Midwest rather than spread evenly.
What is the difference between a boiler and a furnace?
A furnace heats air and a blower distributes it through ductwork. A boiler heats water or makes steam, which circulates through pipes to radiators or baseboard units. A boiler system has no ducts and no blower, so it cannot provide cooling, filtration or ventilation.
Can you add air conditioning to a house with baseboard heat?
Yes, but there is no existing ductwork to reuse, so the options are installing a duct system from scratch or using ductless mini splits. That absence of ducts is the main reason mini splits are common in hydronically heated housing.
Is baseboard heating expensive to run?
It depends on the fuel the boiler burns and local prices, not on the emitter type. Oil-fired systems are common in the Northeast and expose households to a volatile fuel price. Electric resistance baseboard, a different product from hydronic baseboard, has its own cost profile tied to electricity rates.
Methodology and limitations
Installed equipment figures are EIA Residential Energy Consumption Survey 2020, table HC6.1, final data released March 2023. Heating oil prices are EIA series W_EPD2F_PRS_NUS_DPG.
- RECS 2020 remains the current vintage for equipment data; the 2024 survey’s heating and cooling tables are due in spring 2027 See what the 2024 survey release covers.; we do not extrapolate it forward.
- The steam and hot water category groups several emitter types and fuels.
- National shares conceal strong regional concentration in this category particularly.
Sources
- US Energy Information Administration, Residential Energy Consumption Survey 2020, table HC6.1.
- US Energy Information Administration, weekly heating oil series W_EPD2F_PRS_NUS_DPG.
The HVAC Brief is an independent trade publication. We do not sell equipment, take manufacturer advertising, or accept payment for placement in our research. Corrections welcome.
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