Ask an HVAC Expert: Brett in Whitney, CA, “Why Is My Furnace Going out Before My House Heats up?”

why is my furnace going out whitney, CABrett in Whitney, CA is stuck in HVAC limbo—his furnace turns on, but it keeps going out before the temperature reaches the number on his thermostat. He says:

I keep setting my thermostat to 70, but as soon as the temperature in my house hits 68, the heat stops blowing. Why can’t I get my house as warm as I want it, and what can I do to stop having this problem with my furnace shutting off? A few years back, I switched from a gas furnace to a heat pump system, but this is the first year I’m having problems with it.

First of all, Brett, I’m sorry to hear this. I know furnaces that just won’t rise to the number on the thermostat are incredibly frustrating. But I’m glad you let me know that you’ve been using a heat pump instead of a regular furnace. There’s no easy fix for you here, but I think I know exactly what the problem is.

Heat Pump Unhappiness

A heat pump can be a wonderful thing, kind of like an air conditioner in reverse that costs less money than gas furnaces and is better for the environment. But, it also has so many electrical parts that when it breaks, it quickly turns frustrating and mysterious.

Think of a heat pump as a crossing guard, telling heat to either leave or come into your house. When it’s cold out, a heat pump extracts the little bit of heat in the air outside and pumps it into your home, doing the opposite when it comes time for summer. Heat pumps don’t need combustion to create warm air like traditional furnaces.

Because heat pumps rely on taking heat from air outside, they’re ideally suited for milder climates, like the one Brett has up there in Whitney, between Roseville and Lincoln. Whitney’s too small for its own weather report but, like Roseville, it has a Mediterranean climate, where the average daily high in January is a relatively mild 53 degrees. That’s warm enough to make a heat pump viable, but cool enough to make a homeowner like Brett seriously unhappy when his furnace keeps stopping two degrees below the temperature he wants.

Don’t Rely on Plan B

The hard truth of this matter is that Brett’s heat pump sounds like it’s broken. The reason he’s still getting any warm air at all from it is that all heat pumps have a secondary heating source, a “plan B,” that provides extra heat if there isn’t enough warmth in the air outside. This is usually radiant heat, and it’s extremely inefficient.

Radiant heat isn’t generated by warming the air like combustion furnaces and heat pumps do. Instead, it uses electricity to charge an object that radiates heat into the space around it. When it comes to an HVAC system like Brett’s, this sort of warmth is usually generated by electric strips similar to plug-in space heaters. This equipment creates a major risk for having a high electric bill at the end of the month.

On most thermostats that use them, you’ll find an indicator light or something else on the screen that lets you know the system has reverted to secondary or auxiliary heat. These heaters are only in place so that you can stay warm while you call a trained HVAC technician to fix whatever is wrong with the primary system, which in this case is the heat pump. Brett needs to stop relying on electric strips to heat his house immediately if he wants to avoid paying a gigantic electric bill, even considering the mild Whitney winter he lives in.

Go the Extra Two Degrees

In Brett’s case, I strongly suspect that the heat pump has gone out altogether and the thermostat has recognized the primary heat is gone and is trying to limit the expensive use of secondary heaters by stopping two degrees too soon. This is a restriction commonly built into thermostats to protect homeowners against incredibly high electric bills. It also has the added benefit of passively alerting them that something has gone wrong with the heat pump.

So there we have it. While, yes, a furnace going out before it reaches the temperature Brett set can be a bit frustrating, it’s probably better than spending an entire winter in Whitney paying massive heating bills. In a way, Brett’s thermostat has done him a favor by letting him know there’s something funky up with the heat pump. The trouble now is how to fix it.

As I’ve cautioned in the past, it can be really foolish to try and fix a heat pump without being a trained HVAC professional. Heat pumps have so many more electrical parts than gas furnaces, which makes them a risk for painful accidents like shocks. Their parts are also complex and expensive. While we don’t have nearly enough information to diagnose Brett’s exact heat pump problem, I strongly recommend that Brett, and anyone else who has a furnace that keeps going out, call a trained HVAC professional immediately. I can think of plenty of other ways to spend the money you’ll save, especially in a great place like Whitney.

A furnace that fails to hit the temperature you set on the thermostat is frustrating. Let the trained HVAC professionals at Bell Brothers take care of it for you today.