A CHP unit is a system that generates electricity and useful heat at the same time from a single fuel source. The acronym stands for combined heat and power, and the technology is also called cogeneration. Instead of producing electricity at a power plant and heat from a separate boiler, a CHP unit does both jobs in one place, capturing heat that would otherwise be wasted. This dual output is what makes CHP units significantly more efficient than conventional setups.
How a CHP Unit Works
In a conventional power plant, burning fuel generates electricity, but roughly half the energy in that fuel escapes as waste heat through exhaust gases and cooling systems. A CHP unit recovers that heat and puts it to work, typically for space heating, hot water, or industrial processes. The result: total system efficiencies of 65 to 80 percent, with some installations approaching 90 percent. By comparison, using grid electricity plus a separate on-site boiler only achieves about 50 to 55 percent fuel efficiency.
Every CHP unit contains a few core components. The prime mover is the engine or turbine that burns fuel. A generator converts that mechanical energy into electricity. A heat recovery system captures thermal energy from the exhaust and cooling circuits. A digital control system manages the balance between electrical and heat output, and an acoustic enclosure keeps noise levels manageable, especially in settings near occupied buildings.
Types of Prime Movers
The prime mover is the heart of any CHP unit, and the choice depends on the scale of the installation and the fuel available.
- Reciprocating engines are the most common for small and mid-sized systems. They range from as little as 1 kW for residential use up to about 10 MW for commercial and light industrial sites. High-speed versions (1,200 RPM) handle loads up to around 4 MW, while low-speed models can reach 80 MW.
- Gas turbines cover a wide range, from 500 kW to 300 MW, making them suitable for large industrial facilities, hospitals, and university campuses.
- Microturbines are compact units sized between 30 kW and 250 kW individually, though multiple units can be packaged together to reach about 1,000 kW.
- Steam turbines span from 50 kW to several hundred MW. They pair well with solid fuel boilers and are common in heavy industry where biomass, coal, or process waste streams are available.
- Fuel cells generate electricity through an electrochemical reaction rather than combustion. Available in sizes from 5 kW to 2 MW, they convert hydrogen into electricity and water, producing very low emissions. The hydrogen can be supplied directly or created on-site by reforming natural gas, propane, or methanol.
What Fuels a CHP Unit
Natural gas is by far the most common fuel, largely because it’s widely available and burns cleanly. But CHP units are flexible. Reciprocating engines and gas turbines run well on biogas captured from landfills or wastewater treatment digesters. Steam turbine systems can burn nearly any solid, liquid, or gas fuel, which is why they show up in sawmills running on wood waste or factories burning process byproducts.
Hydrogen is an emerging option, particularly for fuel cell CHP units. Because fuel cells produce electricity without combustion, their only direct byproduct is water, making them appealing for sites targeting near-zero emissions.
Sizes: From a Single Home to a Factory
CHP units scale dramatically. At the smallest end, micro-CHP systems designed for residential or small multifamily buildings produce between 1.2 and 4.4 kW of electricity while simultaneously delivering 13,000 to 42,000 BTU per hour of thermal energy as 160°F hot water. That’s enough to cover the heating and a portion of the electricity needs for a modest apartment building. These units adjust output by varying engine speed, ramping up or down as demand shifts throughout the day.
At the industrial end, gas turbines and steam turbines can generate hundreds of megawatts. Large manufacturing plants, refineries, and district heating networks commonly use CHP systems above 5 MW. Mid-range systems between 1 and 5 MW serve hospitals, universities, hotels, and data centers, places with steady, simultaneous demand for both electricity and heat.
Trigeneration: Adding Cooling
Some CHP units go a step further by adding cooling to the mix, a setup known as trigeneration or CCHP (combined cooling, heat, and power). The trick is an absorption chiller, which uses waste heat instead of electricity to produce chilled water. Exhaust gases from the prime mover can drive the chiller directly, or the heat can first be converted to hot water, which then powers the chiller indirectly.
This is especially valuable in warm climates or in facilities like hospitals and data centers that need year-round cooling. Instead of waste heat sitting idle during summer months when space heating isn’t needed, the absorption chiller converts it into something useful, keeping the overall system efficient regardless of season.
Environmental Benefits
Because CHP units extract more useful energy from each unit of fuel, they produce less carbon dioxide per unit of output than conventional separate systems. The reduction can be dramatic. One study of a biogas-fueled CHP system found that its average CO₂ emission factor was 0.22 kg per kilowatt-hour, compared to 1.53 kg per kilowatt-hour for a conventional setup of separate power generation and thermal production. That’s roughly an 85 percent drop in emissions.
Even natural gas CHP systems, which are the most common, deliver meaningful carbon savings simply by using fuel more efficiently. The EPA notes that CHP’s higher fuel efficiency directly translates to lower greenhouse gas output per unit of energy delivered, making it one of the more practical near-term strategies for reducing emissions from buildings and industry.
Financial Incentives in the U.S.
Installing a CHP unit involves significant upfront cost, but federal tax incentives can offset a portion of the investment. Starting in 2025, the Clean Electricity Investment Credit replaced the older Energy Investment Tax Credit. The base credit is 6 percent of the qualified investment. Projects that meet prevailing wage and registered apprenticeship requirements can multiply that up to 30 percent. An additional 10 percentage points is available for meeting domestic content requirements for steel, iron, and manufactured products, and another 10 percentage points for systems located in designated energy communities.
These credits apply broadly to clean electricity technologies and are not limited to CHP specifically, but high-efficiency CHP systems that meet the emissions criteria can qualify. The credit is also eligible for direct payment or transfer, which helps entities that don’t have enough tax liability to use the credit themselves.
Where CHP Units Are Most Practical
CHP delivers the greatest value where a facility has a consistent, simultaneous need for both electricity and heat. Hospitals run 24/7 and need hot water, steam for sterilization, and reliable power. Manufacturing plants often have thermal processes running alongside heavy electrical loads. Universities and large residential complexes combine heating needs with steady baseload electricity demand. Wastewater treatment plants are a natural fit because they produce biogas from the treatment process, which can fuel the CHP unit directly.
The economics become less favorable when heat demand is seasonal or intermittent, because the system’s efficiency advantage depends on actually using the recovered heat. A building that only needs heating four months a year won’t capture the same savings as a facility with year-round thermal demand, unless it adds an absorption chiller to use that heat for cooling during warmer months.