Power outages are likely when massive winter storms are bearing down. It’s important to be safe while trying to stay comfortable at home. You may have seen an outlet on your furnace and wondered: Can my car battery power my furnace during a power outage?
Here’s what you need to know before you pick up an extension cord and attempt this fire hazard.
Our Neighbor’s Question
Neighbor: I have an inverter for my EV (electric vehicle). There’s a plug on my furnace. If power goes out, can I run an extension cord from my car to my furnace to fire the furnace back up?
Answer: Me: Not just, No. Hell, No.
Why Can’t I Plug My Car Battery Power Outage?
Long story short, you can’t energize your furnace from your car battery–even if you have an inverter–via the plug on the furnace because that plug is an ‘Outie.’ Not an ‘Innie.’
The device in question is the “furnace switch.”
It has an outlet and a switch. The reason it is configured like this is to (1) enable a tech to plug in a light or tool and (2) de-energize the furnace without having to launch a CSI-level investigation in the breaker panel.
This switch (Outie) is hardwired and energized from the breaker panel. The furnace is designed to be energized from the panel only.
Fire Hazard
Electricity vibrates. It is way hotter than you think. The majesty of the modern world is harnessing the firestorm of electron transfer in these little wires running through the tinder box of studs in our homes. It’s literally a miracle.
The reason plugging your EV into the furnace switch is a fire hazard is because it might actually work. Therein lies the problem.
While the furnace may fire up during a power outage, you’ve energized the furnace along with the entire circuit back into the panel.
The panel is designed to be an Outie.
What happens if the power comes back on and electrons come flooding back into your system is there are two power sources feeding a system designed–directionally–for one. This can backfeed power to the grid and that can be dangerous.
Transfer Switch
To use an alternate power source for your home, you need a device called a transfer switch. This is kind of like a sub-panel to the main panel that mechanically isolates the main panel from the transfer switch for events like the power coming back on.
The transfer switch feeds several circuits, often 6 to 8, and sends current through existing wiring.
Could a car be used as a battery pack for a house or HVAC system? As long as Direct Current (battery) is inverted to Alternating Current (home systems) via a transfer switch or inverter, sure.
Back to Fire
Setting up a car as back-up power and installing a transfer switch is not a DIY job and should be done by a qualified, licensed professional.
Don’t Trust Facebook “Experts”
I doublechecked my gut instinct in a professional group I’m in. People who I thought should know better did not know better. While many of them responded with a wide variety of sort-of-smart-sounding answers, many of them were still wrong answers.
What’s an Inverter?
Car and tool and lawn mower batteries are all “direct current.” All the stuff in your house is designed to work on “alternating current.” An inverter is a box of wires and transformers and stuff that turns DC into AC.
Summary
- No, don’t try to power a furnace with a car battery.
- It’s a potential fire hazard
- The plug and “light switch” on your furnace/air-handler is called a Furnace Switch
- Outie, not Innie
- What you can and cannot plug into it
- Call a Pro
