The gas does the heating; what needs electricity is the circulating blower and the control board, and a US Department of Energy field study puts that at 422–548 W depending on which motor is in the cabinet. That is a few hundred watts rather than a few thousand, and it is why a furnace is the best-value load in a winter outage. It is also why this site will not hand you a green light: of the 12 published US machines here, 11 come out marginal and 1 refuses outright.
What caps those rows is a missing number rather than a failed test. The figure it is waiting on is the locked-rotor current of a direct-drive blower motor, and we went looking for it three separate times — through manufacturer motor catalogues and original-equipment electrical data tables — without finding one. On every table we opened that carries a locked-rotor column at all, that column belongs to the compressor.
The two running figures come from one federal field study of furnace blower motors. The empty rows are empty on purpose, and each carries the date the search behind it was last run.
Older split-capacitor blower — heating mode548 W Official spec · verified 2026-08-01 · medium confidence
The conventional permanent split-capacitor motor still in most cabinets more than a few years old.
Brushless variable-speed blower — heating mode422 W Official spec · verified 2026-08-01 · medium confidence
The same study measured the brushless permanent-magnet motors using 126 W — twenty-three per cent — less in heating mode. In circulation-only mode the gap is far larger, and so is the drop in airflow.
Locked-rotor current of that motorNot found in the sources we checked no figure to date
The figure a surge verdict would be computed from. Three rounds of searching are recorded on this field, naming the catalogues and data sheets that were opened.
Minimum circuit ampacity, from the furnace maker1,702 VA Official spec · verified 2026-08-01 · medium confidence
A furnace manufacturer’s stated circuit requirement at 115 V, with a band across the range from 943 to 1,760 VA. It describes a conductor, not a running draw.
Official spec · verified 2026-08-02 · gas furnace blower record · DOE field study + manufacturer spec sheets
The number that is there instead, and why it is not a surge figure
Furnace spec sheets carry minimum circuit ampacity, and the manufacturer prints the formula beside it: 1.25 times the circulator blower amperes, plus the inducer blower amperes. That 1.25 is the continuous-load factor from conductor sizing — it exists so a wire does not run warm for hours, and it says nothing about the first tenth of a second. Sizing a battery from it overshoots substantially, which is safe; multiplying it by a start-up factor to manufacture an inrush is neither safe nor meaningful, because it compounds one safety margin with another and prints the result as physics.
A furnace blower against the published US library, computed on this build
The load-ratio column explains little here. A machine at fourteen per cent of continuous output lands in the same state as one at ninety-one per cent, because most of these rows turn on a surge ceiling against a start-up demand we have found no published figure for — and the engine caps a motor load in that condition at marginal rather than passing it.
EcoFlow DELTA Pro 3 × gas furnace blower548 W runningTight fit14%
capped: no start-up figure
The largest machine in the library, at a seventh of its continuous output, and still not a pass. The cap is doing all the work.
Very likely in electrical terms, and this library will not confirm it. A federal field study puts a furnace blower at 422 W to 548 W in heating mode, which most mid-size machines carry comfortably on running watts. But no machine here earns a green verdict: eleven of twelve come out marginal and one refuses, because a motor load with no stated start-up current is capped at marginal by our engine rather than passed.
How many watts does a furnace blower use?
Between 422 W and 548 W in heating mode, and which end you get is set by the motor rather than the furnace. A US Department of Energy field study measured brushless permanent-magnet motors using 126 W — twenty-three per cent — less than conventional split-capacitor motors doing the same job. The figure on the furnace spec sheet is usually minimum circuit ampacity instead, which is a wiring requirement and runs far higher.
Why is every machine on this page marginal rather than a pass?
Because the start-up demand is unknown, and our engine will not treat unknown as harmless for a motor. Direct-drive furnace blower motors are listed with an amperes column and no locked-rotor column, in a full-line motor catalogue, a major maker’s heating and cooling catalogue and an air-handler technical guide alike; the original-equipment tables that do carry locked-rotor current carry it for the compressor instead. Until that figure is measured, a green verdict here would be an assertion rather than a calculation.