The verdict, in one paragraph
Two published figures bracket the whole question. Taco publishes its 006e ECM circulator at a maximum operating power of 44W, 0.54A at 120V — and that circulator is the component that must keep running for heat to reach the radiators. Navien publishes its NCB-190/060H condensing combi at 120V AC, 60Hz, maximum power consumption up to 15 amperes, which is a nameplate maximum of roughly 1,800 watts. Both numbers are honest and they describe different things: the first is what the system draws to move heat, the second is what the circuit must be sized for at full modulation. Size your battery against the first and your wiring against the second, and hydronic heat becomes the cheapest heating system in an American house to back up.
The published figures
| Component | Published electrical figure | What kind of figure it is |
|---|
| Taco 006e RECIRC, ECM circulator | 44 W max operating power; 0.54 A; 120 V, 50/60 Hz | A real maximum draw for one pump |
|---|
| Navien NCB-190/060H condensing combi | 120 V AC, 60 Hz; maximum power consumption up to 15 amperes | A nameplate maximum for the whole appliance |
|---|
| Taco 00 Series cartridge circulators (007, 0010, 0013) | No watts, amps or voltage published on the product page | Not published — see below |
|---|
| Taco 560 Series zone valves | 24 VAC powered, with isolated end switch | Voltage only; no VA figure published |
|---|
Manufacturer figures, cited under Sources. The 15-ampere figure is a maximum, not a steady draw — 15 A at 120 V is about 1,800 W, which is our arithmetic and is a circuit-sizing number rather than a consumption number.
The number nobody publishes
The most common circulator in American basements is a conventional permanent-split-capacitor cartridge pump — a Taco 007 or similar — and Taco does not publish a wattage, an amp rating or a voltage for the 00 Series on its product page at all. The only electrical descriptor is a horsepower range of 1/40 to 1/6 and the phrase “Direct Drive-Low Power Consumption”, with no figure attached.
What Taco does publish is a comparison. Its ECM product copy states that the high-efficiency motor “reduces power consumption by up to 85% compared to equivalent AC permanent split capacitor circulators”. So the manufacturer's own claim places a conventional circulator at several times the 44W of its ECM equivalent. We will not turn “up to 85%” into a specific wattage, because that is arithmetic the manufacturer declined to do.
The practical instruction is the one this site gives for every appliance where the catalog is quiet: read your own nameplate. A circulator has a label on the motor housing, and it will tell you more than any brand page.
Why a nameplate maximum is not a consumption figure
“Up to 15 amperes” on a combi boiler is the same species of number as the MCA on a heat pump: it exists so an electrician sizes the branch circuit correctly, and it describes the worst case with every internal component at maximum. A condensing combi contains its own circulating pump, a variable-speed combustion fan and an electronic control board, and the figure covers all of them at full output simultaneously.
That matters because sizing a battery against a nameplate maximum buys an enormous amount of capacity you will not use. It is the same error the heat pump page warns about — how much power a heat pump uses works through why MCA is not consumption. The difference is that for a heat pump the real figure is still thousands of watts, and for hydronic heat it is tens.
What actually has to keep running
- The circulator. No pump, no heat, regardless of whether the burner fires. This is the 44W component on an ECM system.
- The burner and its controls. On gas, an igniter and a board. On oil, a burner motor and pump, which is a meaningfully larger load than a gas igniter.
- Zone valves or zone pumps. Taco publishes its 560 Series as 24 VAC powered, which comes from a transformer on the boiler rather than from a separate circuit.
- The thermostat. Usually powered from the same 24 V transformer, occasionally by batteries.
Everything in that list is on the boiler's own circuit, which is why a transfer switch rather than an extension cord is the right answer for almost every house.
Boiler versus furnace versus heat pump
| Heating system | What the electricity does | Realistic backup difficulty |
|---|
| Boiler, hydronic | Moves water with a pump; fires a burner | Easiest in the house |
|---|
| Gas or oil furnace | Moves air with a blower against duct resistance | Harder — a blower is a far bigger motor than a circulator |
|---|
| Heat pump | Runs a compressor, and strip heat behind it | Hardest — kilowatt-scale, and no portable battery solves it |
|---|
A qualitative comparison, not a measurement. The published figures behind each row are on the furnace page and the heat pump page.
The one thing hydronic heat does better than anything else
Water holds heat. A hydronic system that has been running carries a tank, a loop and a set of radiators or a slab full of warm water, and that mass keeps releasing heat for a while after the burner stops. A forced-air system has no such reservoir — when the blower stops, the heat delivery stops instantly.
It is also the reason the pipe-freezing deadline is different for a hydronic house, and not in a comforting way: the heating loop itself is full of water, and a long outage in deep cold puts that loop at risk along with the domestic plumbing — keeping pipes from freezing without power covers the deadline.
Sizing a battery for a boiler
- Read the circulator's own label rather than the boiler's. The pump is what has to run.
- Add the burner controls, generously. An oil burner motor is the component to check carefully; a gas igniter is not.
- Ignore the appliance nameplate maximum for capacity sizing, and use it only to confirm the inverter can supply the worst case. Anything over 1,800W continuous clears a 15-ampere nameplate.
- Solve the connection before the capacity. A hardwired boiler needs a transfer switch or an inlet, and that is the purchase most households have not made.
- Then add the rest of the house. With heat at tens of watts, the refrigerator and the lighting are the loads that actually determine the battery you buy — how many watts to run a house puts them together.
The short version
A modern ECM circulator is published at 44 watts, which makes hydronic heat the cheapest heating system in the house to keep alive. A combi boiler's published nameplate maximum of up to 15 amperes is a circuit-sizing figure, not a consumption figure, and sizing a battery against it wastes money. The real constraint on a boiler is not watts at all — it is that the whole system is hardwired, and a battery with nothing to plug into is not backup power.
