Comparing the Energy Costs and Emissions of 3 Types of Water Heaters

When MEP engineers design plumbing systems for buildings, they have many hot water options to choose from – each with advantages and disadvantages. However, if you are looking for ENERGY STAR labeled water heaters three main types are available:

• Electric heat pump with storage
• Gas heater with storage
• Tankless Gas Heater

These three options are economical and use energy inputs that are available as public utilities. On the other hand, building owners using #2 or #4 fuel oil for water heating must schedule regular truck deliveries.

In this article, we will compare the three types of water heaters based on emissions and operating costs. The comparison is based on a heating output of 100 terms, with emission factors provided by Local Law 97 of 2019 and typical electricity and gas prices for New York.

Electric Heat Pump with Storage Tank

Electric heat pumps with a capacity greater than 55 gallons must have an energy factor of 2.20 or greater to qualify for ENERGY STAR labeling. To provide 100 terms of heating with an EF of 2.20, this heat pump must consume the electrical equivalent of 45.45 terms – 1,332 kWh.

• Local Law 97 provides an emission factor of 0.000288962 tCO2-e per kWh, which applies to grid electricity use.
• A commercial electricity price of 20 cents/kWh is typical in New York.

In this case, the heat pump would have accumulated an energy cost of $266 after providing 100 terms of heat, while producing emissions of 385 kg of CO2-eq. However, as the heat pump runs on electrical energy, both emissions and operating costs can be reduced with clean generation – on-site solar power is an option.

According to LL97, the 385 kg of emissions would add $103 in fines ($268 per metric ton), reaching a total cost of $369. However, these costs can be reduced by using solar energy:

• Assume that half of the electricity comes from a solar photovoltaic system, assuming a cost of US$0.08/kWh due to financing, operation and maintenance.
• The cost of energy would drop to $186 and emissions would halve, reducing the penalty to $52. The total cost is now $238.

Gas heater with storage tank

When using a storage gas heater with a capacity greater than 55 gallons, the minimum EF for an ENERGY STAR label is 0.77. To provide 100 terms of water heating, the unit would consume 129.87 terms of natural gas.

• Local Law 97 provides for an emission factor of 0.00005311 tCO2-e per kWh.
• The natural gas price of US$1.20 per thermoelectric plant is typical in New York.

In this case, we obtain an energy cost of $156 and emissions of 690 kg CO2-eq. Although the operating cost is lower compared to an electric heat pump that operates entirely from the grid, emissions are higher by almost 80%.

In this case, the 690 kg of emissions adds US$185 to the building's LL97 fine, and the total cost is US$341. The electric heat pump has a higher cost when using 100% of grid electricity (US$369 ), but this can be reduced with solar energy. This flexibility to change power inputs is not available when using gas water heaters.

Tankless Gas Heater

All tankless gas heaters must have an EF of at least 0.90 to qualify for ENERGY STAR. To provide 100 thermal water heating, this unit would consume 111.11 thermal water. As the fuel is natural gas as in the previous calculation, the same emission factor and energy cost are used.

For an energy consumption of 111.11 terms, we obtain a cost of US$ 133 and emissions of 590 kg CO2-eq. The Local Law 97 Penalty associated with these emissions is $158 and the total cost is $291. Since the tankless heater has a higher EF than the storage heater, both the energy costs and emissions are reduced (0.77 EF vs 0.90 EF). However, a tankless gas heater is also limited by not being able to easily switch its power input.

Comparison Summary

The following table summarizes the energy inputs, energy costs, emissions and LL97 penalties for the three types of heaters – electric heat pump, storage gas heater and tankless gas heater.

This is a very simplified example, but it demonstrates how the choice of water heater and its energy consumption can affect operating costs and emissions. To accurately estimate these values ​​for a building, you can hire a professional MEP design and energy modeling service.