I woke up at 4 AM to a cold house and a loud whirring noise. I dragged myself out of bed to figure out what was going on. I walked downstairs and found that the fireplace was on. What was happening?

Our central HVAC unit is an all-electric split unit: the main machine is in a utility closet and it’s piped to a heat exchanger outside. A pump attached to the indoor unit collects the condensation and regularly pumps it to a tube outside.

The room adjacent to the utility closet is underground, and so stays damp. To prevent mold and mildew, we run a dehumidifier at night. In order to not have to manually dump out the collection bin, I ran a tube from the dehumidifier to the HVAC pump.

Usually, that setup works brilliantly. Water from the HVAC and dehumidifier is collected in one box and is pumped out automatically. But that doesn’t work when it’s 25°F outside and the outside tubing is frozen solid.

When the pump can’t do its thing, it runs constantly, and while it’s running it draws power from the thermostat, so it’s effectively kaput until the pump stops. And the pump won’t stop until the water has been pumped out.

Fortunately, getting the electric heat working again was simple enough: I disconnected the dehumidifier and drained the water from the pump box. Et voilà, the heat was back.

But why was the fireplace on?

A year after we moved into this house, I realized the old propane fireplace was leaking, so I had it replaced. The replacement was a fancy model with a remote control. The remote control has an automatic thermostat option: set a temperature and the remote kicks on the fireplace when the temperature drops below a threshold.

It just so happened that the remote was sitting in line of sight of the fireplace, so when the central heat failed, the fireplace kicked on automatically. If not for that bit of serendipity, who knows what sort of frozen disaster I would have woken up to.

So, my tip to you: if you have a gas fireplace with a remote control thermostat, set that sucker up so it can kick on the fireplace below a temperature. 69°F is a nice threshold. That way, if you have a bizarre chain of disasters or simply a power outage, your house stays warm, or at least not frozen.