What does a kW cost per hour?
One kilowatt running for one hour is one kilowatt-hour, and one kilowatt-hour costs whatever your utility charges. Everything else is bookkeeping — here is how to do it right.
The direct answer: running a 1 kW load for one hour consumes 1 kWh of electricity, so it costs exactly your all-in rate per kilowatt-hour. At $0.1846/kWh that is 18.5 cents an hour. Scale it linearly: a 3.5 kW load costs 3.5 × $0.1846 = $0.65 per hour. The formula is one line:
cost per hour = power (kW) × your $/kWh
Two things trip people up, and neither is the multiplication. The first is the unit itself — kW and kWh are different quantities and the phrase "kW per hour" mixes them. The second is the rate: the number printed largest on your bill is usually not the number you actually pay. This guide fixes both, then turns the result into per-hour, per-day and per-month figures for the electrical loads a house actually runs.
kW and kWh are not the same thing
Kilowatts measure power — the rate at which a device draws energy right now, like the speed on a speedometer. Kilowatt-hours measure energy — power multiplied by time, like miles travelled. Your utility sells you energy, so it bills kWh; your equipment nameplate describes power, so it lists kW or watts. That is why "kW per hour" is not a real unit: dividing power by time again gives you nothing useful. What people mean when they search it is either "what does one kWh cost" or "what does this kW-rated device cost to run for an hour", and those are the same question with the same one-line answer above.
Watts convert to kilowatts by dividing by 1,000: a 1,450 W dehumidifier is 1.45 kW. And because HVAC is a mixed US-unit world, it helps to remember the bridge to heat: 1 kW = 3,412 BTU/h, so a 3-ton (36,000 BTU/h) cooling capacity is 10.55 kW of heat moved, not 10.55 kW of electricity drawn. Confusing the two is the single most expensive mistake in this arithmetic. The ton / BTU / kW converter and the capacity reference table keep the thermal side straight.
Finding the kW your device actually draws
There are three reliable routes, in descending order of trustworthiness.
- Nameplate watts. Best case: the plate says 1,450 W and you are done — 1.45 kW.
- Volts × amps. For a 240 V condenser drawing 12.5 running amps: 240 × 12.5 = 3,000 W = 3.0 kW. For motor loads this slightly overstates real draw because of power factor, so treat it as a ceiling. Read the rated-load amps (RLA) from the plate; do not open an energized panel — that is work for a licensed electrician.
- Capacity divided by efficiency. The HVAC-specific route:
kW = capacity (BTU/h) ÷ (EER × 1,000)in cooling, orkW = capacity ÷ (COP × 3,412)in heat-pump heating. A 36,000 BTU/h unit at EER 11.4 draws 36,000 ÷ 11,400 = 3.16 kW. This is the method the AC running-cost calculator and the heat-pump running-cost calculator use, and it is the one to trust when you have a spec sheet but no clamp meter.
Your real rate is not the advertised rate
This is where most per-hour estimates go wrong by 20–40%. Utility bills separate a supply (or generation) charge from delivery (or distribution) charges, and then add fixed customer charges, riders and taxes. The advertised cents-per-kWh is usually the supply half only. The honest way to get your all-in rate is arithmetic on the bill you already have:
all-in $/kWh = total bill $ ÷ kWh used
A bill of $214.83 for 1,164 kWh gives 214.83 ÷ 1,164 = $0.1846/kWh — and that is the number to put in every calculator on this site. Two refinements are worth making. If a fixed monthly customer charge is large relative to your usage, it inflates the average in low-usage months, so a summer bill gives a better cooling rate than a shoulder-season one. And on a time-of-use plan the average understates cooling, because air conditioning runs during the expensive afternoon peak — use the peak rate for cooling scenarios and the off-peak rate for a heat pump running overnight.
What household electrical loads cost per hour
Worked at the $0.1846/kWh derived above. Substitute your own rate: the column scales linearly, so at half that rate every figure halves.
| Load | Typical draw | Cost per hour |
|---|---|---|
| Electric resistance strip heat (10 kW bank) | 10.0 kW | $1.85 |
| 3-ton AC compressor + condenser fan (EER 11.4) | 3.16 kW | $0.58 |
| 3-ton heat pump in heating (COP 3.1) | 3.40 kW | $0.63 |
| Ductless mini-split, one zone at part load | 0.75 kW | $0.14 |
| Whole-house dehumidifier | 0.72 kW | $0.13 |
| Furnace blower, ECM motor at low speed | 0.14 kW | $0.03 |
| Furnace blower, older PSC motor | 0.55 kW | $0.10 |
The table is worth reading for the ratios rather than the cents. Electric resistance heat costs roughly three times what a heat pump costs per unit of delivered heat, which is the whole economic argument for a heat pump and for setting a sensible balance point on a dual-fuel system. And the blower rows explain a bill mystery: an older PSC blower left in "fan on" mode all summer draws about four times what a modern ECM does at low speed.
From an hour to a month
Add hours and days and nothing else changes:
monthly $ = kW × hours per day × days × $/kWh
That older PSC blower left running continuously: 0.55 kW × 24 h × 30 days = 396 kWh, which at $0.1846 is $73.10 a month for air circulation alone. Switch it to auto so it runs only during the roughly 9 hours a day the system calls: 0.55 × 9 × 30 = 148.5 kWh, about $27.41 — a $45 monthly swing from one thermostat setting. Apply the same arithmetic to the compressor and you have the seasonal number: the honest input is compressor runtime, not hours the system is switched on, since on a mild day a right-sized unit runs perhaps 40–60% of the time. A smart thermostat’s usage report is the easiest source for that; the setback-savings tool estimates what changing the schedule does to it.
Sanity checks before you trust a number
Three quick tests catch nearly every error in this kind of estimate. First, compare against the bill: if your per-appliance estimates sum to more kWh than the meter recorded, an assumed runtime is too high. Second, check the unit: a figure near 10 kW for a 3-ton air conditioner means you converted thermal capacity instead of electrical draw — the electrical number should be roughly 3 kW. Third, check the rate: an all-in rate far below your bill average usually means you used the supply charge alone. When those three agree, the arithmetic is trustworthy, and it stays trustworthy no matter what happens to energy prices, because the only time-sensitive input is the rate you type in yourself. For the full cooling-season method, see how much it costs to run your AC; for the units underneath it all, BTU explained.
Rate structures and national energy statistics are published by the U.S. Energy Information Administration; efficiency metrics and the test basis behind EER, SEER2 and HSPF2 come from the U.S. Department of Energy and ENERGY STAR.