backup
Backup for a heat-pump house: lock out the strips, then size the machine
A gas furnace on backup is a blower. A heat pump is a compressor plus optional kilowatts of electric strips. Tesla's Powerwall 3 is 13.5 kWh and 11.5 kW continuous. A 10 kW heat kit already fills that. HomeGuide's typical standby is $6,000 to $11,000 installed. Leave the strips off the essentials panel.
A gas furnace that still has gas during an outage needs a blower and an inducer. That is a few hundred watts, which is why the fridge, sump, furnace kit can stay small.
A heat pump is an electric heater that also cools. The outdoor unit wants kilowatts while it runs. Many air handlers also have electric resistance strips, a heat kit, for the coldest hours. A 10 kW kit is 10,000 watts. That is not a surge. It sits there until the thermostat is satisfied.
Backup that was sized for a gas furnace will not cover that house. You either lock the strips off when the street is dark, keep a furnace as the outage heat, or you buy a much bigger machine.
This is electrician and HVAC work. Transfer switches and load-shed contactors are not a Saturday adapter. Whole-home vs essential-only is still the wiring fork. Battery vs standby is still hours versus days. Stay here until the heat pump is on the load list as the watts it actually draws.
The furnace was a blower. This is a compressor.
DOE says today’s air-source heat pumps can cut electricity for heating by about 75 percent compared with electric resistance, like a furnace of coils or baseboards. That 75 percent is why you bought the heat pump. It is also why the strips, if they come on, undo the backup plan. Resistance heat is the expensive way to make warmth, and it is the heavy way to load a generator.
Nameplate math is blunt. Ten kilowatts is 10,000 watts. At 240 volts that is about 42 amps of continuous heat, before the compressor, the air handler fan, the fridge, and the well. A 15 kW kit is 15,000 watts. Ask what kit is in the air handler, in kilowatts, not “emergency heat.”
Tesla’s Powerwall 3-class pack is 13.5 kWh usable and 11.5 kW continuous on their support pages. One pack cannot feed a 10 kW kit and still have headroom for the house. At 10 kW, 13.5 kWh is gone in well under two hours even if nothing else is on.
The EV charger page makes the same point for a 7.2 kW wall box. Strips are that problem with a worse attitude, because they often start themselves when the outdoor unit is cold or locked out.
A dual-fuel setup, heat pump plus a gas furnace, is how some houses keep outage heat on the gas meter. Dual-fuel heat pump is that fork on the energy side. If the gas stays up, the furnace blower is still the small load. If the gas dies with the electric, you are back to the heat pump and the strips.
Battery, standby, or a short list
EnergySage’s storage cost page, the one the battery-vs-standby guide already uses, puts a typical install around $15,647 before incentives for about 13.5 kWh. That is essentials, not a whole electric furnace. First-half 2026 quotes on that page run Tesla around $967/kWh, Enphase around $1,429/kWh, FranklinWH around $1,232/kWh.
EnergySage: solar battery cost
HomeGuide’s 2026 whole-house generator guide puts a typical standby at $6,000 to $11,000 installed, or $9,500 to $24,000 when the run is long or the unit is over 20 kW. Portables are $500 to $2,500, plus $400 to $1,300 for a transfer switch. Their size table puts 7 to 10 kW portables in the “furnace fan” neighborhood, not the “10 kW of strips” neighborhood. 13 to 16 kW is a small whole home. 22 to 25 kW is the air-cooled whole-home band a lot of sales charts start at.
HomeGuide: whole house generator cost
Transfer switch cost installed is the interlock vs ten-circuit vs 200-amp automatic. A 200-amp whole-home switch that still lets the strips pull 10 kW will trip or stall a 10 kW generator. Whole-home on the label is not whole-heat-pump-plus-strips.
Three honest products:
Essentials, strips locked out. Fridge, well or sump, lights, internet, and the heat pump compressor if the battery or generator can carry it. The thermostat cannot call the kit. Load-shed or a setting in the air handler. This is how a single Powerwall or a 10 to 14 kW standby stays honest. The house may be cooler than 70°F. Pipes and people still get heat from the compressor if it can run.
Dual-fuel, gas heat on outage. The heat pump cools and heats while the grid is up. When backup starts, the furnace takes heat if gas is there. The generator sees a blower. Confirm the gas meter actually stayed live last ice storm.
Size the engine or stack packs for the kit. You want 70°F with strips allowed. Count the kit watts plus compressor plus the rest of the house, then buy that. HomeGuide’s over-20 kW install band is the neighborhood. Two or three battery packs is the quiet version, and the invoice multiplies.
Load-shed smart panels is how a smaller machine pretends to be whole-home by dropping the dryer, the range, and, if you program it, the heat kit.
What the quote has to show
Which heat kit, in kW, is in the air handler, and does backup allow it?
Does the thermostat have a backup-heat lockout, and who sets the outdoor temperature where strips are allowed?
Is the heat pump on the essential panel, the main panel, or a load-shed contactor?
Whole-home 200-amp switch, or a short circuit list? Whole-home vs essential is that sentence.
Battery usable kWh and continuous kW, not the sticker. Generator running kW on the fuel you will have.
Carbon monoxide alarms with battery backup, and 20 feet if this is a portable. A heat pump does not make CO. The generator still does.
Who programs the lockout after the install. A setting that resets on a power cycle is not a lockout.
Two envelopes, same ranch
Bid A, essentials and lockout. One 13.5 kWh pack around EnergySage’s $15,647, or a 10 to 14 kW standby in HomeGuide’s common installed band. Heat pump compressor on the short list if the numbers fit. Strips off. EV charger off, same as the charger page. You live in the kitchen and the heat is whatever the compressor can do.
Bid B, strips allowed. 22 kW-class standby, HomeGuide $6,000 to $11,000 typical and $9,500 to $24,000 when it is big or far, or two-plus battery packs. 200-amp switch. Load-shed for the dryer so the kit can run. If Bid B is $8,000 and still has a 10 kW portable, it is Bid A with better stationery.
If Bid A is $12,000 and Bid B is $28,000, ask which one lets the strips close. That gap is the kit, not the brand of generator.
What usually blows the heat-pump backup
Sizing from the old furnace quote. The blower is not the load anymore.
Leaving “emergency heat” enabled so the first cold night dumps 10 kW onto a 13.5 kWh pack. The lights go first.
A 7 to 10 kW portable because HomeGuide listed a furnace fan in that row. Their table assumed a gas furnace fan, not a heat kit.
Whole-home switch, 10 kW generator, strips still in the air handler. The breaker or the engine will decide for you.
Stacking the EV charger and the strips on the same backup. DOE’s typical Level 2 is 7.2 kW. Add a 10 kW kit and you have invented a second house.
No CO alarms because “it’s all electric now.” The generator is not.
What the driveway questions sound like
How many kilowatts is the heat kit, and is it allowed to run on backup?
Where is the lockout, in the thermostat or a contactor, and does it survive a reboot?
Is the outdoor unit on the essential panel, and what is its running watts on the spec sheet?
Battery: usable kWh and continuous kW. Generator: running kW on propane or gas, not the peak sticker.
Does the 200-amp switch still let the strips and the well start together?
Who hangs CO alarms with battery backup if a generator is in this bid?
How do I decide this week?
Read the heat kit off the air handler door, in kW. That number is the first line of the backup bid.
Decide whether strips may run in the dark. If no, lock them out and size for the compressor plus fridge, well, and lights. If yes, buy a machine that can carry the kit.
Compare a ~$15,647 13.5 kWh battery to a $6,000 to $11,000 typical standby using the outage you actually get, hours versus days, from battery vs standby.
Keep the EV charger off backup unless you sized for it on purpose.
Put working CO alarms on every level before the portable leaves the garage. Ready.gov and CPSC still want 20 feet and exhaust away.
If the same crew wants to sell you a bigger heat pump so the house never needs strips, that is an energy bid. Get it in writing next to the backup bid, and do not let either one assume the other exists.