Commercial energy / Buyer guidance
Electric unit heaters: resistance load, controls and heat-pump alternatives
Identify what heats the building, measure operating hours and compare delivered heat without inventing an equipment savings percentage.
Identify the heater before estimating its cost
“Electricity-fired” is misleading terminology for an electric resistance unit heater. Resistance elements turn electrical input into heat at the equipment. A heat pump moves heat and has different temperature-dependent performance. A gas-fired heater uses a fuel burner and requires a different energy calculation. Record the actual equipment type, rating, control arrangement and served area before comparing alternatives.
The DOE heat-pump explanation distinguishes heat movement from resistance heating. Its household examples should not be copied into a commercial project as a promised saving. A commercial selection also needs an actual heating load, operating temperatures, electrical service review and an equipment specification suited to the space.
Measure the duty cycle and the billing exposure
Nameplate kW multiplied by every occupied hour overstates energy use if the heater cycles. Conversely, a short cold-weather run can contribute to the account's billed electric demand if it coincides with other loads. Use trend or meter data where available and record the assumed fraction of time energized. Distinguish fans, resistance stages and any backup elements.
Review doors, loading activity, zoning, setpoints and recovery periods with the facility team. A heater addressing a freeze-protection requirement cannot be switched off simply because the room is unoccupied. Maintain equipment clearances and manufacturer requirements; controls changes should be approved by people responsible for the operation.
Worked example: model energy and demand separately
Hypothetical inputs: a 15 kW resistance heater is energized for 300 equivalent full-load hours over a season. Electricity use is 15 × 300 = 4,500 kWh. At an assumed marginal energy price of $0.12/kWh, the modeled energy cost is $540.
For a comparison only, assume an alternative supplies the same useful heat with an average coefficient of performance of 2.5. Its modeled input would be 4,500 ÷ 2.5 = 1,800 kWh, costing $216 on the same energy assumption. The $324 difference excludes installation, maintenance, demand, backup operation and changes in performance with weather. The COP is a teaching assumption, not a product rating or a predicted annual result.
If either option changes the billing peak, that needs a second calculation using the actual demand tariff. Do not multiply the equipment rating by a demand price for every month unless the equipment changes the account's billed determinant in those months.
A replacement decision record
| Required input | Why it changes the decision |
|---|---|
| Design and operating heat load | Equipment must meet the required conditions |
| Measured run profile | Determines consumption and coincident demand |
| Low-temperature capacity and backup | Can change annual input and service needs |
| Installed cost and electrical work | Can outweigh a small operating difference |
| Comfort and process constraints | Establish acceptable control strategies |
Use the demand calculator only for the electric billing component it describes. Keep capital and engineering assumptions outside that simple model until documented.
Sources and limits
DOE heat pumps supports the technology distinction. DOE re-tuning guidance supports checking controls with operating data. No equipment performance, installation quote or achieved saving is asserted for an actual site.