Material Insights · Understanding the Material World

Building heat recovery: Impact and additionality

Tiny savings per unit that add up across millions

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.

Each unit saves little, but millions of water heaters and air conditioners add up, and in India savings displace coal-heavy grid power or diesel boilers.

Direct Scope 1 and Scope 2 abatement

Favourable

A drain-water unit recovering about 790 kWh a year would avoid about 0.57 t CO2 a year on India's grid at 0.727 t CO2/MWh (FY2023-24 average; calculated), if it displaced electric water heating. The Mumbai hotel chiller project cut about 36 t CO2 in its last six months of reported operation by replacing diesel water heating, and also raised chiller COP by about 20%. Simulations cited in the literature show drain-water units cutting annual water-heating demand by 23 to 31%.23812

Hotel superheat recovery CO2 cut (2003 study) about 36 t in 6 months8 Chiller COP gain about 20%8 Drain-water CO2 avoided about 0.57 t/yr per home (calculated)212 Water-heating demand cut (simulated) 23-31%3

Water and air synergy

Favourable

Condenser heat recovery lowers condensing temperature, and Alfa Laval claims about 3% lower energy use per degree. Diverting condenser heat into water also reduces cooling-tower load and the water it evaporates. Kitchen demand control almost halved fan electricity in the US Army case, and replacing diesel or gas boilers removes local combustion emissions in dense cities.79

Energy saving per 1 C lower condensing temperature about 3% (supplier claim)9 Kitchen fan energy reduced by almost half (about 96,600 kWh/yr)7

Avoided lock-in

Favourable

These measures cut demand without supporting any fossil asset. The caveat is ordering: fitting heat recovery to a new gas water heater can make it harder to justify switching to a heat pump later.4

Sources

  1. Evaluation of Residential Drain Water Heat Recovery Unit (study begun 2010) Sustainable Technologies Evaluation Program (Toronto and Region Conservation Authority), 2017
  2. Modelling the Steady-State Performance of Coiled Falling-Film Drain Water Heat Recovery Systems Using Rated Data (Manouchehri and Collins), Resources 9: 69 MDPI Resources (University of Waterloo authors), 2020
  3. Is a Heat Pump Water Heater Right for Your Home? ENERGY STAR (US EPA), 2023
  4. Engineering and Construction Bulletin 2015-3: Demand control kitchen ventilation US Army Corps of Engineers (via WBDG), 2015
  5. Benefits of superheat recovery on chillers: case study for a hotel installation (Rane and Tandale), 21st IIR International Congress of Refrigeration International Institute of Refrigeration, 2003
  6. Revolutionizing Energy Efficiency for a Leading Hotel Chain in India Alfa Laval India (company case study), 2025
  7. CO2 Baseline Database for the Indian Power Sector, User Guide Version 20.0 Central Electricity Authority, 2024