Furnace Blowing Warm Air, Not Hot Air? (We Have A Fix)

Ossiana Tepfenhart
by Ossiana Tepfenhart

Your home’s HVAC system is one of the most important systems when it comes to your safety, your comfort, as well as your home’s value. That’s why minor issues with your heating system still deserve a lot of attention, even if it’s something that is as simple as a furnace that’s blowing warm air rather than hot air. Speaking of, what does that even mean?

If your furnace is blowing warm air and not hot air, this could be due to your thermostat regulating the temperature in your home. However, there are other reasons why this occurs such as dirty vents, outside air in your vents, poor furnace performance, and having the wrong size furnace for your home.

A little bit of troubleshooting can go a long way when it comes to figuring out your furnace problems. This guide will help you understand what might be going on with your HVAC.

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How Do You Know If Your Furnace Is Doing Its Job?

It’s important to realize that your thermostat might just be doing what it’s meant to do. Thermostats are programmed to signal when HVAC systems should blow out warm air instead of hot as a way of maintaining a steady temperature.

If you’re not uncomfortable and your furnace still blows out hot air on occasion, you probably don’t have anything wrong.

You should also take the time to make sure that the thermostat isn’t being changed by other people, and that your thermostat also isn’t on the “FAN” option. If it’s on “FAN,” it’ll continue to push out warm air even if you don’t necessarily need heat.

How To Fix Furnace Not Blowing Hot Air

What Could Cause Your Furnace To Blow Warm Air Instead Of Hot?

There are several different reasons why you might have an underperforming furnace. To help you troubleshoot your HVAC system, we’re going to parse it out, step by step…

Check Your Thermostat

Let’s say that you turned your thermostat up all the way, but the air is still tepid at best. You know it’s not an issue of temperature regulation or because someone else is readjusting your thermostat. It’s not a matter of the thermostat being on “FAN,” either. What could be going on?

  • Double-check your thermostat’s batteries. This could be a low battery issue. Some thermostats stop regulating heat if they don’t have enough power.
  • Make sure your thermostat is installed correctly. If you recently installed your thermostat, a poor installation could be the problem.
  • Also, triple-check to see if your thermostat is functioning. Sometimes, thermostats just die out. When this happens, you just need to replace your thermostat.

Air Out Your Air Filters

Every home will have HVAC air filters that help remove dust, soot, and other grime from your airflow. They are a necessary part of your furnace’s upkeep and safety…and they’re also one of the most heavily neglected parts of your home.

If your air filters get too dirty, they reduce the airflow that you could get from your furnace. This can turn into overheating at worst, and lukewarm air at best.

The best way to troubleshoot this is to take out your furnace’s filters and clean them. If the airflow now feels a lot hotter, congrats! You solved the problem.

Address Furnace Problems

Another set of issues that crop up could deal with your furnace. Here’s how to troubleshoot each type of furnace:

  • Check your furnace for adequate fuel. If you have a gas furnace, make sure that the gas lines are clean and that you have ample oil to work with your furnace. If you have an electric furnace, check out the voltage that your furnace is receiving and double-check to see if the wiring looks good.
  • Run a quick diagnostic to see if your furnace is overheating. If your furnace is overheating, the breaker inside will trip to prevent an explosion. Should your furnace struggle with this issue, call an HVAC tech immediately. This is a potentially dangerous issue that needs to be addressed.
  • Make sure that there’s power running to the furnace. A quick glance at your circuit breaker will make sure that you actually have everything prepped for your furnace to run well. Sometimes, breaker boxes will have a switch trip that makes it shut down.

Look At Your Air Ducts

Another issue that might lead to warm (rather than hot) air coming out of your furnace deals with the inclusion of outside air.

The most common reason why the air feels warm rather than hot deals with a hole in the air vents that carry the air out of the furnace. If you notice warm air only hitting one of your rooms, check the vents nearby for holes and patch up any you see.

Most of the time, holes in your air ducts happen when your ductwork starts to look worse for the wear. If this is a new home, this should not be an issue.

Finally, Check Your Furnace Size

If you have a brand new home that was just built or a home that was recently expanded, then you might have one last issue causing your lukewarm air.

Most people don’t realize this, but furnaces are actually meant to be sized according to the square footage of your home. If the home is brand new or recently added onto, the issue might be that you have a furnace that’s too small for your house size.

Should you have a furnace that’s undersized, you’re going to need to make a tough decision. You can either grin and bear it, or you can call an HVAC tech and get your furnace switched out. Obviously, the second option would be ideal, but it can cost thousands of dollars to do. If the furnace is new, you might be able to switch it out at a discount.

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Related Questions

How can you tell if your furnace is about to fail?

Furnaces that are on the verge of dying out will have a hard time staying on, may have pilot lights that go out, and also might be prone to overheating.You should also consider getting a new furnace if you notice signs of corrosion, if it starts to emit a strange smell, or if your energy bills are climbing without any legitimate reason as to why.

How often should air filters be replaced in a furnace?

Experts agree that furnace air filters should be inspected at least once a month and replaced when they begin to look threadbare. If you want to try to reuse your filter, make an effort to clean them off before you place them back in their proper area.

How do I figure out what size my furnace is supposed to be?

If you are trying to buy the right furnace size for your home, you really shouldn’t try to size your furnace on your own. The best way to get the right size furnace for your home is to hire an HVAC professional to examine your home and give you information on the proper size and placement of your furnace.Even if you have HVAC knowledge, you probably should leave it to the professionals. In many districts, building codes require having a professional oversee furnace sizing as a part of your home’s construction. Besides, it’s always good to have a professional give their two cents on the matter.

How can I clean my furnace on my own?

Along with changing any filters your furnace may have, it’s a good idea to clean your furnace ducts using a vacuum.If you are comfortable opening up your furnace, you can also take time to remove the blower assembly and wipe it down with some soap and water. Vacuum the blower using a handheld device, put the device back together again, and you should be good to go.

Can you run a furnace without a filter?

The answer to this is a hard no. Running a furnace without the filter will pose a huge risk to your health as well as the functionality of your furnace. You need to have a filter in order to safely and smartly heat your home.

Ossiana Tepfenhart
Ossiana Tepfenhart

Ossiana Tepfenhart is an expert writer, focusing on interior design and general home tips. Writing is her life, and it's what she does best. Her interests include art and real estate investments.

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