How to control your furnace when your thermostat dies

Originally published at: How to control your furnace when your thermostat dies | Boing Boing


If your thermostat malfunctions, you can take its place by connecting the red and white wires behind the thermostat yourself.

This is terrible advice. What if I need to leave the house? Who’s gonna hold the wires then? :clown_face:


You can hold them with some clothespins, that way your home will be a nice toasty 180 degrees when you get there and you can use the 10 bucks you saved not buying a replacement thermostat on the gas bill! Win win.


Add to it that most residential heat pumps or HVAC systems aren’t really rated for continuous duty as well.

Thermostats are more than $10 even for the cheap ones (around Arizona, they start around $20 and go up from there), but even a fancy one is not much more than $150. Oh, and it may not be the red and white wires; those might just short voltage to ground instead of kicking the heat/cool relay, so you risk damaging the unit itself, and service calls like that aren’t cheap, especially if it ends up trashing the unit entirely…

Can you tell that I absolutely hate this style of “easy home living hack” video? They tend to be not very useful, or promote risky ideas that lead to expensive repairs and / or injury.

Edit: after actually watching the video, I still stand by my comments, but it’s still a last resort and Not Recommended for anything but emergency use until a proper replacement can be sourced and installed.


There’s a horde of people desperate to exploit any kind of “hey you can do this did you know?” type stuff and none of them are experts. This person learned that touching 2 wires can complete a circuit. Wow. Let’s make a video showing all the amazing tricks you can do with this knowledge. Sad thing is this is working as the world is a sea of clickbait and we are all bored enough to keep trying and they get views no matter how dumb the content is long as that ad rolls at the front.


Do not like.

It’s correct as far as it goes, and I’m sure his intentions are all for the good. But it doesn’t mention that electric baseboard heaters are often controlled direct, without relays or low-voltage control circuits. You’re feckin with 220 volts there, not 24, but the thermostat looks much the same up front, and coincidentally there’s usually a red wire and a white one. This would be very risky advice in homes with baseboards, and residents that aren’t up on the basics. People get in over their heads. Ought to have a strong caution on that up front and after.

Also what SpaceGhost and Bonivus said.

You should only do this in an emergency, only with a furnace, to keep your place and your people/pets from freezing, until you can get a new thermostat in there ASAP.


Easy hack how to electrocute yourself more like it.

Electric furnaces don’t have on/off switches, you need to turn off the breaker.

If there is a fault in the system, then hopefully a real thermostat would have some provision for shutting off… so you are bypassing a safety feature.

Only 1% (or less) of the population have the necessary wherewithal to muck around with voltages (low or high). Shitty “easy hack how to” videos are a path to death for the other 99%.

Originally had a very dumb thermo, with a mercury bulb and a few discrete parts… upgraded to a 3/7 programmable unit for $40… simple to set, had a filter warning… nothing bling but did the job for 15 years. Then thought I would get all fancy and buy an ecobee … regret wasting that $$.

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To note: Baseboards still only pul 120 per line just 1 is continuously run to the unit and one goes to a Tstat. Hence the eventually 240 to run the actual device, not the thermostat as this would fry it.

Even in an emergency, I wouldn’t resort to this approach. But then again, I have at least 3 spare thermostats lying around in the furnace room and garage. I have learned along the way which of them were easy and did useful things. Not all “smart” thermostats have been designed very well, including one that refused to operate correctly when its AAA batteries died even though power to the thermostat never dropped off.
When I bought the Nest thermostat, it ended a lot of the frustrations with setting schedules and added a few other cool features. Buying the service that they offered to have it professionally installed was a TOTAL waste of money because the technician who showed up didn’t know enough to complete the work and paying for the company that installed our air conditioning and furnace was also wasted because they refused to install a thermostat that they didn’t sell (frustrating).

When they connected the thermostat in this house, they used whatever wire sections they could scrounge up. There’s bits of doorbell wire and line cord in there.

If someone were going to do such an unpleasant temporary jury rig, I suggest doing it at the furnace.

There should be a connector block inside the furnace panel that will either be labeled, or detailed in the manual (which is in a plastic bag attached to the furnace, right?)

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This is horrifically bad advice. First off, if it’s not a proportional control thermostat, you’re dealing directly with 220v 20a power to the heating element, and 110v to the control relay, which is not anything for anyone to be touching together to complete a circuit. There is a reason it’s being controlled with a relay and not someone manually doing it.

If it is a 4-20mA proportional control system, you’d be operating your furnace literally full blast, which is a tremendous waste of gas or fuel oil.

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