Once I purchased my first home, I realized that I needed to do my part in caring for my home appliances. In addition to reading the user manuals for my kitchen appliances and state-of-the-art plumbing system, I realized that I also needed to do a little research about HVAC. Because I had no experience with HVAC systems, I called out a professional to teach me a thing or two. It was fascinating to talk with him, and I was able to take notes about all kinds of important topics, such as maintenance, troubleshooting, and even shopping for a new system. This blog is all about understanding HVAC guidelines.
You want your furnace to run when it's cold outside, but it's possible to have too much of a good thing. HVAC equipment that's correctly operating should run in cycles. Your furnace will turn on when the thermostat calls for heat, run until the temperature increases to your set point, and then shut down once the thermostat stops calling for heat.
If the furnace doesn't shut off or runs for far too long, that can cause numerous problems. In addition to making your home uncomfortable, it's likely to drive up your energy bills and even cause damage to your heat exchanger or other furnace components. If your heat won't shut off, here are the three questions you should be asking.
1. Are You Reaching Your Set Point?
Your set point is the target temperature you set on your thermostat. Your furnace should kick on when the temperature drops below this point and shut back off when it reaches its target. If your furnace keeps running, start by looking at your thermostat. Is the temperature at or above your set point, or is the furnace running constantly without reaching its target temperature?
If the furnace keeps running despite reaching the set point (or the displayed temperature appears incorrect), there's a good chance you have a faulty thermostat. On the other hand, a furnace that keeps running without reaching its target temperature may have another issue. Your thermostat is probably fine in these cases, but your furnace can't keep up with your heating needs.
2. Do You Feel Hot Air?
Put your hand near a supply vent and check for hot air. Your furnace should produce noticeably warmer air than the air near the return vent. You can use a thermometer to measure the difference between the supply and return vents, but you shouldn't need to for basic diagnostics. Instead, simply try to tell if you feel hot air or if the vents simply seem to be pushing room-temperature air.
If you can feel hot air, your furnace is on and running. On the other hand, cool air or air at the same temperature as the return vent means that your furnace is most likely off, but the blower is on. In this case, make sure your thermostat's fan switch is on "auto." If this doesn't solve the problem, there may be a wiring issue or a problem with the furnace control board.
3. Is Your Filter Dirty?
If you've confirmed that your furnace is on and your thermostat's fan setting is correct, your last step should be to check your filter. A dirty filter can restrict airflow, reducing the amount of warm air reaching each room. Although you'll still feel warm air at the vents, it may not be sufficient to reach your thermostat's set point without taking a long time.
Once you've gone through these basic diagnostic steps, it's time to contact a professional. A furnace that runs continuously can lead to sky-high utility bills and even present a hazard to your home, so it's best to call in a professional to resolve this issue as soon as you can. Contact an HVAC contractor if you have questions about your furnace.