Troubleshooting a Furnace Blowing Cold Air

Why is My Furnace Blowing Cold Air?

It doesn’t matter where you live. If the place you live in has any kind of a cold season, then keeping your furnace in optimal working order is crucial.

If your furnace is blowing cold air, it’s sometimes a good idea to get a professional as soon as possible to determine what could be wrong. That said, there are a few simple reasons that your furnace could be blowing cold air and (luckily!) they are issues that you can easily address without a professional.

How Do I Fix My Cold Furnace?

1.     The Pilot Light has Gone Out

Older furnaces have what is called a “pilot light.” The pilot light is a small flame that is kept burning at all times, since it is needed to light the burners in your furnace. Newer furnaces have a much more efficient lighting method that involves using an electric ignitor to create a spark that lights the burners. If your older furnace is blowing cold air, the first thing you should do is check to see whether the pilot light is still lit. If it isn’t, open the panel where the pilot light is located and light the flame. Wait a little while to see if your furnace resumes blowing warm air.

2.     Lack of Gas

If the pilot light on your older furnace keeps going out after you relit it, then the problem could be the gas supply. A quick check will tell you whether the gas supply is turned on—that is, in a parallel position to the supply pipe.

3.     Fan Switch

When your home seems to be maintaining a comfortable temperature overall, but your furnace is still blowing cold air, check the fan settings on your thermostat.

The fan will have two settings: “on” and “auto.” Having the fan set to “on” means that the fan will be on continually, even when the actual furnace is not. In this case, the fan will simply keep blowing cold air through your vents. Switch your fan setting to “auto.” When the fan is set on “auto”, it will only come on when the thermostat detects a change in ambient temperature that is different from what is set. This temperature change will cause the furnace to turn on, which means warm air will soon begin blowing out your vents.

4.     Clog

Newer furnaces have what is called a condensate drain. The purpose of the condensate drain is to remove the condensation that forms during heating. If the drain develops a clog, the furnace burners will not be able to light, which means the furnace can’t do its job maintaining the temperature. This problem is fixed by simply removing the clog.

5.     Running on Empty

If you have an oil-fired furnace that is persistently blowing out cold air, check the oil supply. If the tank is empty, the furnace will continue to push air through the house, but it won’t be heated because the burners aren’t ignited. To fix this, just turn off the furnace, carefully top up the oil, and turn the furnace back on. Once there is oil in the tank, the burners should fire up and heat up the furnace.

6.     Low Battery

Another reason your furnace could be blowing cold air is because the battery in your thermostat could be low. If it is low, the temperature detection process could be affected. Try changing the battery to see if that fixes the problem.

7.     Clogged Filters

It’s easy to lose track of taking care of the filters in your gas furnace. A clogged filter can cause your furnace to have to work harder in order to push heated air throughout your home. If the filter is left clogged for too long, it can actually cause your system to overheat, which will in turn cause a safety feature called the “limiter switch” to kick in. The “limiter switch” turns off the burners, thus making sure your home doesn’t burn down.

If you use disposable filters, you can fix this issue by simply replacing the filter. If you have a reusable filter, then you will need to clean the filter with warm soapy water and allow it to dry thoroughly before putting it back in the furnace.

8.     Blocked Vent Pipes

Newer furnaces have pipes that lead outside. These are usually constructed of PVC and can sometimes get blocked with debris from outside or even ice. In this case, all you really need to do is make sure the outside vent is free of debris—the clog isn’t going to be further up the pipe, since air blows out these pipes instead of in.

9.     Leaky Ducts

Ducts often run through colder places in your house, like the basement or the attic. A leaky duct could draw in air from these cooler places, which in turn causes this cooler air to lower the temperature in your furnace. Searching for small leaks can be tricky but, once you have found it, you can generally patch it with duct tape. Larger leaks, on the other hand, may require duct replacement or repair by a professional.

10.  Computerized Controls

A newer heating system will often have a computerized control panel. If you are having a problem with cold air, it may be just that you need to reset the system in much the same way that you would reboot a personal computer when you are experiencing a software issue. If the furnace is still blowing cold air after you have reset the system and explored all the other possibilities listed here, then you may need to speak to a professional.

11.  A Clog in the Oil Filter

If you have an oil furnace, its filter can get clogged the same way the air filter can on a gas furnace. A clogged filter can affect the ignition process, which will result in your furnace blowing out cold air. It is possible to clean this filter yourself if you know how, but the process is messy. If you need to clean the filter, it might be a good idea to leave it to a professional.

Like most machines, furnaces require a certain amount of upkeep to allow them to do their jobs at peak efficiency. While there are a number of furnace repairs that definitely require the attention of a professional, there are some minor repairs—such as those listed above—that you can do when your furnace starts blowing cold air.

If it’s time to replace your furnace and you’re looking to save money on your BC Hydro bill, contact Lockhart Industries and ask about heating and cooling your Duncan to Victoria, BC home with a high efficiency air to air heat pump (check rebates available here) or a geoexchange system.