Why does my furnace sometimes turn off at night?

Person shivering under a blanket because their furnace shut off.

Here's Why Your Furnace Stops Working at Night

One Sunday morning, there were five different HVAC service companies working at homes on the same block of a residential street all with Carrier 90% furnaces. All had condensation draining issues and I still had three other clients to get to that day!

As the winter season gets colder, our furnaces work the hardest during the coldest parts of the day, usually in the wee hours of the morning. Unfortunately, this is also when the furnace may shut down because it cannot drain the condensation as fast as it is produced.

Furnaces may start up and run fine at the beginning of the season as the blockage absorbs the condensation and may even drain with no negative results, but because it is especially colder at night, it may turn off because the condensation cannot drain.

Other reasons why your furnace keeps shutting off include:

  • Your furnace is too large for your home and is short cycling
  • Your furnace's heat exchanger is overheating due to low airflow
  • Your furnace's flame sensor is dirty

What Should I Do if My Furnace Shuts Off Randomly?

Oftentimes, when the furnace stops working, owners will begin frantically searching for a service company to get the heat back on. By the time a technician arrives, the furnace may have already started back up and running fine. This is because it has had time to drain slowly and doesn’t produce as much condensation. If it happened once, it will happen again within the same time frame.

If you get your furnace checked annually and know that there is nothing wrong with your furnace, then you may be more confident to wait until it turns on again later. However, if you suspect that it needs repair, you may need to call a furnace technician in Commerce City for help.

How Do Furnaces Work?

A 90% efficient condensing furnace produces condensation. They are piped outside through two-three-inch PVC pipes. One pipe is the air intake needed for the combustion of the main burners. The second is the exhaust pipe to expel flue gases…much like a car. These furnaces only lose 90 to 100 degrees of heat through the exhaust when compared to older furnaces losing four to five times more heat through the flue. With this in mind, the 90% furnace can’t heat the flue piping as the older furnaces, thereby creating condensation, hence the PVC piping (plastic piping).

The condensation, with design, simply drains back to the furnace and is routed through a series of rubber hoses to an integrated condensation trap. These furnaces have a motor strong enough to pull in the fresh air and expel flue gases. So a ‘trap’ is needed to keep the furnace from pulling negative pressure on the draining of condensation and monitored by a pressure switch, a safety device.

Concerns With Condensation Traps

Herein lies the concern- the intake pipe is always pulling air inward for combustion to happen and at the same time, moisture, dust, dirt, and leaves can be pulled in as well. This debris travels through the piping, into the combustion chamber and is mixed with the condensation. As mentioned everything drains into the ‘trap’. Over time, especially during the summer, this debris and condensation sit at the bottom of the ‘trap’ decaying, drying out, and forming an almost cement-like blockage.

Which Furnace Brands Have Condensation Traps?

All the name brand systems, Carrier, Lennox, Rheem, Amana, etc., all have these condensation traps. However, from experience, Carrier seems to have the biggest design flaw or issues with these ‘traps’. By the same token, the only real prevention is annual maintenance as recommended by all manufacturers.

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If you are experiencing concerns with your furnace, call Sunshine Home Services at (303) 622-5526 or complete an online form to schedule an annual or repair heating service.

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