The short answer
An electric steam boiler turns about 99% of the power it draws into steam, against roughly 80–85% fuel-to-steam for a typical gas-fired boiler, but electricity usually costs several times more per Btu than natural gas. With our assumed prices of $6.00/MMBtu gas and $0.08/kWh power, 1,000 lb of steam costs about $7.30 from gas and $23.70 from electricity; electricity breaks even only near 2.5 cents/kWh at that gas price. Electric wins where combustion is not allowed, loads are small, power is cheap or off-peak, or low-carbon electricity is needed to meet emissions targets.
- Electric boilers are close to 100% efficient at the point of use: Bosch states over 99% for its ELSB, and Cleaver-Brooks says nearly 100% at all operating points.
- Break-even rule: electric steam costs the same as gas steam when electricity’s price per MMBtu is about 1.2 times gas’s (ratio of 99% to 82% efficiency).
- Low-voltage resistance boilers top out around 3–3.4 MW per unit (Cleaver-Brooks HSB 3,375 kW; Fulton FBZ 3,000 kW); medium-voltage electrode boilers reach 102 MW (Cleaver-Brooks MVE, 13.2–25 kV).
- One kW of electric input makes about 3.5 lb/hr of steam: Cleaver-Brooks rates the 3,375 kW HSB at 11,813 lb/hr.
- On the 2025 US average grid (771.5 lb CO2/MWh, EPA), electric steam emits more CO2 than an 82%-efficient gas boiler; it emits less where the grid or supply is below about 480 lb CO2/MWh.
| Factor | Electric (resistance or electrode) | Gas-fired (firetube or watertube) |
|---|---|---|
| Efficiency at point of use | About 99%: no stack loss; small radiation and blowdown losses | About 80–85% fuel-to-steam (HHV) without condensing; more with economizer |
| Energy cost driver | Electricity price per kWh, plus demand charges | Gas price per MMBtu or therm |
| Site emissions | None at the boiler | CO2, NOx and CO from combustion; air permit usually required |
| Lifecycle CO2 | Depends on grid or power contract | 53.06 kg CO2 per MMBtu of gas burned (EPA) |
| Unit size | Resistance: kW to about 3.4 MW at 480–690 V. Electrode: 1–102 MW at 13.2–25 kV | From a few BHP to over 1,000,000 lb/h |
| Infrastructure | Large electrical service and transformer; no gas line, stack or combustion air | Gas service, stack, combustion air, burner management |
| Response | Fast output change; thyristor control on some units | Burner turndown typically up to about 10:1 |
| Maintenance | Elements, contactors, fuses; electrode boilers need conductivity control | Burner tuning, flame safeguard checks, fire-side cleaning |
| Water treatment | Still required; electrode boilers depend on controlled conductivity | Required |
The options side by side
1Electric resistance (element) boilers
Best for: Small to medium steam loads up to about 3 MW, sites with no gas or no combustion allowed, and point-of-use steam.
Immersion heating elements in an insulated vessel boil the water directly. Units run at low voltage (480–600 V in North America; Bosch ELSB at 380/400/690 V) and are fully packaged. Published ranges include Cleaver-Brooks Model CR 12–563 kW (up to 1,969 lb/hr) and Model HSB 1,560–3,375 kW (up to 11,813 lb/hr, 15–250 psig), Fulton FBE 12–180 kW, FBL 12–1,000 kW and FBZ 90–3,000 kW, Bryan BH 60–3,000 kW, and Bosch ELSB 350–8,300 kg/h at up to 24 bar.
- No flue, no burner, no combustion permit.
- Quiet, compact and quick to install where power is available.
- Element staging or thyristor control matches output to load.
- Energy cost per pound of steam is usually higher than gas.
- Large units need thousands of amps at 480 V; utility upgrades can dominate project cost.
2Electrode boilers
Best for: Large electric steam loads (megawatts) at sites with medium-voltage supply.
An electrode boiler uses the boiler water itself as the resistor: current flows between electrodes through the water and heats it. Cleaver-Brooks’ Model MVE is a high-voltage jet-type electrode boiler rated 1 to 102 MW, up to 340,000 lb/hr, at 13.2 to 25 kV and 100 to 450 psig operating pressure. Output is modulated with a shield gate, and water conductivity is controlled automatically.
- Scales to the size of large gas-fired watertube boilers.
- Connects at medium voltage, so current and cable size stay manageable.
- Fast response suits demand response and surplus-power programs.
- Needs a medium-voltage service and protection scheme, and qualified MV electricians.
- Water conductivity control is part of the output control; treatment must be well managed.
Maker’s page: e.g. Cleaver-Brooks Model MVE
3Gas-fired steam boilers
Best for: Most industrial steam where natural gas is available and priced well below electricity.
Gas-fired firetube and watertube boilers remain the lowest-cost steam source at typical US prices. Makers publish fuel-to-steam efficiencies in the low to mid 80s percent: Fulton 82% for the FBS, Hurst at least 81% for its Scotch marine boilers and Miura about 85%. Economizers and condensing heat exchangers add more. Many current gas boilers are listed as able to burn hydrogen blends or biogas.
- Lowest energy cost per pound of steam at typical US gas-to-power price ratios.
- Any size from a few BHP to over 1,000,000 lb/h.
- Large water volume (firetube) buffers sudden steam draws.
- On-site CO2 and NOx; permits and low-NOx burners add cost.
- Needs stack, combustion air and burner management upkeep.
Worked example: cost per 1,000 lb of steam
The assumptions below are ours, chosen for illustration only. Replace them with your own delivered gas price, electricity energy rate, demand charges and boiler data. The US EIA publishes current state and national industrial gas and electricity prices.
- Assumption: saturated steam at about 125 psig made from 227°F deaerated feedwater. That takes about 1,000 Btu per lb (steam enthalpy about 1,193 Btu/lb minus feedwater about 195 Btu/lb), so 1,000 lb of steam needs about 1.0 MMBtu delivered to the water.
- Assumption: gas boiler fuel-to-steam efficiency 82% (HHV), in line with makers’ published figures.
- Assumption: electric boiler efficiency 99%.
- Assumption: natural gas $6.00 per MMBtu delivered.
- Assumption: electricity $0.08 per kWh energy charge, demand charges excluded.
| Step | Gas-fired boiler | Electric boiler |
|---|---|---|
| Energy into the water | 1.0 MMBtu | 1.0 MMBtu = 293 kWh (3,412 Btu per kWh) |
| Divide by efficiency | 1.0 ÷ 0.82 = 1.22 MMBtu of gas | 293 ÷ 0.99 = 296 kWh |
| Multiply by assumed price | 1.22 × $6.00 = $7.32 | 296 × $0.08 = $23.68 |
| Result per 1,000 lb | About $7.30 | About $23.70 (3.2 times gas) |
Break-even: at $6.00/MMBtu gas, electricity would have to cost about $0.025/kWh (2.5 cents) to match. Put the other way, at $0.08/kWh, gas would have to cost about $19.40/MMBtu. A quick test for any prices: convert electricity to $/MMBtu by multiplying $/kWh by 293; electric steam is cheaper when that figure is below about 1.2 times the gas price per MMBtu.
Sensitivity: off-peak or interruptible power at $0.04/kWh gives about $11.80 per 1,000 lb, which is close to gas at $10/MMBtu (about $12.20). This is why hybrid plants run electric boilers when power is cheap and gas boilers the rest of the time.
Emissions and decarbonisation
Burning natural gas releases 53.06 kg CO2 per MMBtu (EPA). In the example, 1.22 MMBtu of gas per 1,000 lb of steam is about 64.7 kg, or 143 lb of CO2. The electric boiler’s 296 kWh carries whatever the electricity carries: at EPA’s 2025 US average of 771.5 lb CO2/MWh that is about 228 lb, and at the California (CAMX) subregion figure of 436.7 lb/MWh about 129 lb.
- Crossover: electric steam emits less CO2 than an 82%-efficient gas boiler when the electricity supply is below about 480 lb CO2/MWh.
- With a renewable supply contract or on-site generation, electric steam can be close to zero CO2 at the point of use; Bosch cites ELSB installations run on surplus self-generated or green power.
- Electric boilers have no site NOx or CO, which can remove the need for low-NOx burners and simplify air permits.
- Hybrid designs (Fulton VSRT-E, Viessmann Vitomax HS-EH, or an ELSB beside a gas UL-S) let a plant switch energy source as prices and grid carbon change.
Electrical service: what a steam load needs
One kW makes about 3.5 lb/hr of steam, so electric boilers draw large currents. Three-phase current is kW × 1,000 ÷ (1.732 × volts). A 10,000 lb/hr load needs about 2,960 kW of input in our example.
| Supply | Full-load current | Typical boiler type |
|---|---|---|
| 480 V three-phase | About 3,560 A | Resistance element (one or two large units) |
| 13.8 kV three-phase | About 124 A | Electrode boiler |
- Resistance boilers are low-voltage equipment: Cleaver-Brooks lists 480–600 V for the CR and HSB; Bosch lists 380, 400 and 690 V for the ELSB.
- Electrode boilers connect at medium voltage: Cleaver-Brooks lists 13.2 to 25 kV for the MVE.
- Check transformer capacity, switchgear, cable routes, harmonics from thyristor control, and utility lead times before you choose electric.
When electric beats gas
- No natural gas at the site, or the gas service upgrade costs more than the electrical one.
- Combustion not allowed or impractical: clean rooms, labs, some hospitals and urban buildings without a stack.
- Small or point-of-use steam loads where a gas boiler would cycle heavily and run at low efficiency.
- Cheap off-peak, interruptible or self-generated power, often run alongside a gas boiler.
- A corporate or regulatory requirement to cut on-site combustion emissions, backed by a low-carbon power supply.
How we compared them
We used makers’ published ratings for electric and gas boilers (Cleaver-Brooks, Fulton, Bryan, Bosch, Viessmann), EPA’s 2025 GHG Emission Factors Hub for CO2 factors, and US DOE for steam basics. The cost example uses assumed prices that we state openly; replace them with your own tariff and gas contract. Calculations are ours and show every step. We do not sell boilers or energy.
Frequently asked questions
Is an electric steam boiler cheaper to run than gas?
Usually not at typical US prices. Electric boilers are about 99% efficient, but electricity costs several times more per Btu than gas. At our assumed $6.00/MMBtu gas and $0.08/kWh power, electric steam costs about 3.2 times as much per pound.
How efficient is an electric steam boiler?
Close to 100% at the point of use. Bosch states over 99% for its ELSB electric steam boiler and Cleaver-Brooks describes its electric boilers as nearly 100% efficient at all operating points. Blowdown and radiation losses still apply.
How many kW do I need per pound of steam?
About 1 kW for every 3.5 lb/hr. Cleaver-Brooks rates its 3,375 kW Model HSB at 11,813 lb/hr. Exact figures depend on pressure and feedwater temperature.
What is the difference between an electrode boiler and an electric resistance boiler?
A resistance boiler heats water with immersion elements at low voltage and is practical up to about 3 MW per unit. An electrode boiler passes current through the water itself at medium voltage (13.2–25 kV for the Cleaver-Brooks MVE) and scales to around 100 MW.
Are electric boilers better for the environment?
They have no site emissions. Their CO2 depends on the electricity: on the 2025 US average grid, electric steam produces more CO2 than an efficient gas boiler, but on a supply below about 480 lb CO2/MWh, or with renewable power, it produces less.
Can I run electric and gas boilers together?
Yes. Hybrid plants run electric boilers when power is cheap or surplus and gas boilers otherwise. Bosch cites sites running an ELSB alongside a gas-fired UL-S, and Fulton and Viessmann sell hybrid gas and electric boilers.