How Hot Can Ductwork Get?

The air gets heated up to 170 F. You shouldn’t be able to comfortably touch the ductwork, but, at the same time, nothing bad is going to happen if you have a properly functioning HVAC system. However, if the unit does not have good insulation, then the ductwork will get too hot and will be impossible to touch. 

Below you will find everything that you need to know about heat and ductwork, starting from the description of the actual heating process and ending with the most common reasons for overheating.

The Heating Process – How Does It Work?

What exactly happens once you turn your furnace on? 

As soon as you switch the unit on it starts either igniting fuel (gas, oil) or heating elements (electricity). Once the air inside the system becomes hot, a fan blows it first through the heat exchanger and then – into the actual ductwork.

The heated air then gets distributed to the vents around your house.

Of course, when the air is first heated, it is extremely hot. But how hot can the system get?

How Hot Can Ductwork Get?

Once the combustion occurs and the air gets heated up, it can have a temperature between 140 F and 170 F. That is very hot and you certainly wouldn’t want such air to fill up your rooms.

Thankfully, once distributed into the house, the air starts quickly cooling down. In fact, in a lot of cases, it will begin to get colder while it is still traveling through the ductwork.

It is a good thing, as the hot air has time to cool down, but, at the same time, if your ductwork is not properly insulated, you will end up losing too much heat before the air gets to the actual room that needs to be heated.

Tip: if you have noticed that your furnace now needs more time than before to bring the room to a comfortable temperature or that the heating throughout the rooms is uneven, then it looks like something is wrong with the system. You can call a heating contractor if you want to fix the issue in the shortest timeframe. 

Naturally, the temperature of the duct is going to be higher close to the furnace and the system will get a bit cooler, once the air gets a chance to travel away from the furnace.

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In a nutshell, the temperatures inside the ductwork are high and you shouldn’t be able to comfortably touch the main trunk that is located just above the main unit. 

By the way, the air coming out of the system should not be lukewarm. If it is – there might be a leak somewhere in the ductwork. As a result, cool air gets to enter the system and the hot air gets to escape the ducts before getting delivered to the room.

In fact, HVAC systems usually leak around 10% of the supply air that is moved through the ductwork and about 12% of the return air.

That is why you should consider sealing and properly insulating the ductwork in your house. 

The Importance of Proper Insulation

In places with poor insulation, the ductwork will get very hot, up to a point that it might burn you if you accidentally touch the system.

However, proper insulation is important not only for safety reasons but also because it will help you save a ton of money on energy bills and will, overall, help the system work more efficiently.

If your ductwork goes through quite a few unconditioned spaces throughout the house (like the attics and crawlspace), you will end up losing a lot of warm air while it travels through these cold areas. 

The truth is that ducts located in the attic can reduce the whole system’s efficiency by about 20%. And that’s quite a lot of lost energy and money.

The joints that have not been sealed will end up not only leaking the hot air but also the cool air from ‘outside’ will find its way into the system through the same places.

3 Reasons Why Your HVAC Can Overheat

A unit can definitely overheat and, in the most severe cases, catch fire. While the latter will, most likely, never happen, overheating issues are relatively common in HVAC systems.

This usually happens because of one of these three reasons.

  • A clogged air filter

The main ‘job’ of an air filter is to prevent dust and other things from entering the HVAC system and damaging it. However, once the filter becomes clogged and dirty, it will no longer be able to allow the air to freely go through the system.

As a result, your unit will not have adequate airflow and all of the components will be forced to work even harder (sometimes, at full capacity). This might cause the system to overheat.

Solution: make sure to change the air filter at least every 3 months. However, if you have pets, a lot of people living in the house, or a family member that smokes inside the house, you might have to change the filter every month.

  • A refrigerant leak

A refrigerant is a thing that turns warm or hot air into cool air. If you want your HVAC system to work its magic, then there should always be an adequate amount of refrigerant in it. Sometimes, a leak might occur. In such a case, the system will begin to overwork which, in its turn, can lead to overheating.

Solution: unfortunately, you will not be able to fix the problem on your own, as any refrigerant-related issues have to be handled by a professional. 

  • The condenser coils are dirty

The condenser is the part of the HVAC system that is located outside. It has coils that release any heat that has been collected inside your house into the outside world. There should be a good amount of space around the condenser, in order for it to function properly.

Of course, the heat-releasing coils can get dirty. As a result, this part of the system won’t be able to release the heat into the outside air and the unit might overheat.

Solution: you should follow a regular maintenance schedule. The whole system needs to be cleaned every once in a while, but you should try to invite a technician over a bit more often so that they can quickly check if every part of the unit is working properly.

Frequently Asked Questions

Can ducts touch wood?

In normal circumstances, ductwork is not able to char or ignite the wood. So, you don’t have to insulate the wood that is located close to your unit.

What kind of tapes can withstand heat?

When choosing a tape to use on your ductwork, you should find the one that can tolerate extremely high temperatures. A lot of the options available, including regular duct tape, might not be able to withstand the heat.

Usually, foil tape is a great choice, if you need to seal the ducts. Be careful when looking for the right tape as a non-foil option might catch fire.

What is a heat duct?

Heat ducts are heat-resistant ductwork fittings. These things can endure extreme temperatures. For example, there are plenty of high-temperature flexible ducts available on the market nowadays. They can be made out of a wide range of materials – PVC, stainless steel, rubber, fiberglass, silicone, and so on.

What is the temperature rise of a furnace?

It is the difference between the temperature of the heated supply air and the return air. The temperature rise has to be measured during the installation process and you would have to make sure that the number is within the range indicated on the furnace rating plate.

How hot can duct tape get?

You should not use duct tape on the ductwork or to secure the insulation as it is not the right kind of tape for the job. But if there is a strip of duct tape somewhere on the unit, it will be able to withstand about 200 F before melting.

How hot should the air coming out of an air conditioner vent be?

The air coming out should, in general, be around 15-20 degrees cooler than the air that had been taken in. For example, if the temperature in your house is 75 F, then you can expect the air coming out of the vent to be anywhere between 55 F and 60 F.

To Sum Up

You wouldn’t want to be inside your air ducts when the heating unit is on. The temperatures inside can be as high as 170 F. However, from the outside, the actual ductwork should not be extremely hot.

In fact, if the ducts have proper insulation, you should be able to touch them without getting burned.

The temperature of the ductwork is going to be a bit higher in the part that is closer to the furnace. But once the air gets a chance to travel through the system, it will have enough time to cool down to a comfortable temperature.