# Combined heat and power: Impact and additionality

Halving CO2 on dirty grids, raising it on clean ones

Source page: https://www.materialinsights.org/energy/e_chp/rc-impact/

What this tab covers The impact and additionality lens: direct emission cuts, side benefits for water and air, and the risk of prolonging the life of a polluting host plant.

Gas CHP roughly halves CO2 compared with separate production on a fossil-heavy grid, but the benefit shrinks as grids decarbonise and it commits the host to gas for the life of the plant.

#### Direct Scope 1 and Scope 2 abatement
Mixed

CHP raises on-site Scope 1 emissions while cutting Scope 2 from grid power. DOE gives an effective CHP emission rate of 468-523 lb CO2 per MWh (about 0.21-0.24 t, calculated) after crediting the displaced boiler, against average US marginal grid emissions above 1,400 lb (about 0.64 t, calculated). EPA's 1 MW engine example emits 4,200 t a year against 8,300 t for separate heat and power (EPA's unit labels are inconsistent). DOE credited US CHP with 241 Mt CO2 and 1.8 quads of fuel avoided a year.^[1](https://betterbuildingssolutioncenter.energy.gov/sites/default/files/attachments/CHP_Reciprocating_Engines.pdf)^[3](https://19january2025snapshot.epa.gov/chp/chp-benefits)^[4](https://iac.university/file/general/CHP%20TAP%20Training%20for%20IACs%20-%20February%2011%202021.pdf)
 Effective CHP CO2 468-523 lb/MWh (about 0.21-0.24 t/MWh, calculated)^[1](https://betterbuildingssolutioncenter.energy.gov/sites/default/files/attachments/CHP_Reciprocating_Engines.pdf) US marginal grid CO2 above 1,400 lb/MWh^[1](https://betterbuildingssolutioncenter.energy.gov/sites/default/files/attachments/CHP_Reciprocating_Engines.pdf) US CHP CO2 avoided 241 Mt/yr^[4](https://iac.university/file/general/CHP%20TAP%20Training%20for%20IACs%20-%20February%2011%202021.pdf) 1 MW engine example 4,200 vs 8,300 t CO2/yr^[3](https://19january2025snapshot.epa.gov/chp/chp-benefits)

#### Water and air synergy
Mixed

On-site generation avoids US grid transmission and distribution losses of about 5.3% on average. Steam turbine plants and big power stations use cooling water, while engine CHP rejects most heat into the host's hot water system. Engines add local NOx in towns and cities, so catalysts and permits matter.^[1](https://betterbuildingssolutioncenter.energy.gov/sites/default/files/attachments/CHP_Reciprocating_Engines.pdf)^[3](https://19january2025snapshot.epa.gov/chp/chp-benefits)
 Avoided grid losses (US average) about 5.3%^[3](https://19january2025snapshot.epa.gov/chp/chp-benefits)

#### Avoided lock-in
Unfavourable

Gas CHP is a bridge at best. Its abatement depends on what the grid would otherwise emit: against a coal-heavy grid it cuts emissions sharply, against a grid rich in renewables it can raise them. Engines and turbines run for many years, so a 2026 gas CHP may still run when the grid is far cleaner. Biomass, biogas and hydrogen-ready engines, and heat pumps for the low-grade share, reduce this risk.^[1](https://betterbuildingssolutioncenter.energy.gov/sites/default/files/attachments/CHP_Reciprocating_Engines.pdf)^[6](https://old.etipbioenergy.eu/images/ETIP_Bioenergy_Factsheet_Biomass_CHP_facilities.pdf)

#### Sources

1. [Reciprocating Engines, CHP Technology Fact Sheet Series (DOE/EE-2764)](https://betterbuildingssolutioncenter.energy.gov/sites/default/files/attachments/CHP_Reciprocating_Engines.pdf) US Department of Energy, 2023
2. [CHP benefits (archived page, snapshot of 19 January 2025)](https://19january2025snapshot.epa.gov/chp/chp-benefits) US EPA Combined Heat and Power Partnership, 2025
3. [CHP TAP training for Industrial Assessment Centers](https://iac.university/file/general/CHP%20TAP%20Training%20for%20IACs%20-%20February%2011%202021.pdf) US DOE CHP Technical Assistance Partnerships, 2021
4. [Biomass CHP facilities (factsheet)](https://old.etipbioenergy.eu/images/ETIP_Bioenergy_Factsheet_Biomass_CHP_facilities.pdf) ETIP Bioenergy, 2018

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_chp/index.md)
- [Overview](https://www.materialinsights.org/energy/e_chp/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_chp/correlation/index.md)
- [Science and thermodynamics](https://www.materialinsights.org/energy/e_chp/rc-sci/index.md)
- [Engineering and integration](https://www.materialinsights.org/energy/e_chp/rc-eng/index.md)
- [Economics and contracts](https://www.materialinsights.org/energy/e_chp/rc-econ/index.md)
- [What to track](https://www.materialinsights.org/energy/e_chp/tracking/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_chp/links/index.md)