How Hot Can Ductwork Get? - HVAC BOSS (2023)

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.

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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.

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.

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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.

How Hot Can Ductwork Get? - HVAC BOSS (1)

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.

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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
How Hot Can Ductwork Get? - HVAC BOSS (2)

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
How Hot Can Ductwork Get? - HVAC BOSS (3)

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.

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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.

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How hot does an HVAC duct get? ›

Hot air ducts made of silicone can normally handle temperatures ranging up to 550° F. In some cases, depending on the makeup of a specific hot air duct, the range can be even higher up to 750° F.

How hot can galvanized ductwork get? ›

Galvanized steel is suitable for high-temperature applications typically up to 392°F (200°C). Use at temperatures above this level can result in the peeling of the zinc at the intermetallic layer.

What is duct temperature? ›

Duct Temperature Sensor - The duct static temperature sensor measures air temperature in the ductwork. The solid-state temperature sensing devices are commonly used in HVAC applications that are controlled by direct digital control or a modern building automation system.

How hot should heat from registers be? ›

Bottom line: the supply air temperature at a room supply register is typically 100°F-110°F. Measured at the furnace the supply air temperature typically ranges 40-70 °F above the return air temperature.

Can HVAC overheat? ›

Three of the most common reasons why HVAC systems overheat are clogged air filters, refrigerant leaks, and dirty condenser coils. These issues force your heater or air conditioner to work harder to produce the temperature and quality of airflow you need, which results in the system overheating.

How hot does forced air get? ›

Forced warm air systems rapidly provide heat with register temperatures in the 120° to 140° F (49° to 60° C).

Can heating ducts catch fire? ›

Fires very rarely originate directly within a duct -- though it can happen. Instead, fires may occur through electrical issues, candles, or even children playing with matches. However, even though the fire doesn't start in the air duct, it can be fueled significantly by the air duct.

How high can duct tape handle heat? ›

Hot surfaces: Surfaces that reach temperatures over 140°F cause the adhesive to soften, lose its strength, and slip from the attachment. Cold surfaces: Similarly, duct tape does not work well in extreme cold. Freezing temperatures cause the adhesive to harden which diminishes its sticking power.

What is the maximum temperature for galvanized steel? ›

Low-temperature climates are an appropriate use for hot-dip galvanized steel. In long-term, continuous exposure, the recommended maximum temperature is 392 F (200 C). Continuous exposure to temperatures above this can cause the outer free zinc layer to peel from the underlying zinc-iron alloy layer.

What is a good supply temp? ›

While there isn't any perfect temperature you should set your HVAC system to, there is an ideal temperature difference between the supply and return air, which should be between 16 and 22 degrees Fahrenheit.

How hot does a furnace plenum get? ›

For a forced air fossil fuel furnace I would expect to see 35-70*. If the return air was 50* you could easily have a plenum temp of 95* and if you had really good air flow across the exchanger, the return could be 60* and still have that discharge temp.

What is temperature rise in HVAC? ›

Temperature rise is the difference of air temperature between the conditioned return air and the heated supply air sent from the furnace. Temperature rise is part of the initial setup of a furnace.

How strong should heat come out of vents? ›

The air coming out of the vent when heating should be 85 to 90 degrees for most homes, or 15 to 20 degrees warmer than the air in the room. The air is hotter when it leaves the furnace – and the maximum allowable temperature rise through a furnace is usually 30 to 70 degrees based on the manufacturer's specifications.

Is 22 too high for heating? ›

But this all boils down to the following: the perfect temperature for your heating is somewhere in between 18 and 22 degrees depending on preference - with the lowest number possible being better for your wallet.

How hot should heat be coming out of vents with heat pump? ›

Heat pumps usually produce air that is 85-92°F. This is plenty warm to heat your home to your desired 72°F. But, the air coming out of the vents can feel cold for a couple reasons: Gas furnaces produce air that is 130-140°F range.

How do HVAC technicians stay cool? ›

How to Keep HVAC Techs Cool in Summer
  1. Encourage Breaks. One of the simplest ways to keep the heat from overpowering your workers is to limit the amount of time they spend in it. ...
  2. Stay Hydrated. ...
  3. Dress for the Weather. ...
  4. Train Workers on Heat Exhaustion. ...
  5. Work in Groups. ...
  6. Insulate Work Vans.
27 Jul 2020

What happens when HVAC is overcharged? ›

The Consequences of an Overcharged Air Conditioner

One major problem is that when there's too much refrigerant, it won't be able to properly switch between gaseous and liquid state, and more of it will remain in liquid state. This will harm the system's efficiency and affect cooling in the house.

Is HVAC tough on body? ›

Working as an HVAC technician does involve some risk of bodily harm. HVAC technicians suffer more on-the-job injuries than workers in many other professions because they are often working with heavy equipment, extreme heat and/or cold, not to mention they are subjected to hazardous materials from time to time.

Is 80 F too hot for a house? ›

I recommend trying to keep your house below 80 degrees at all times during the summer. At 80 degrees, there's a good chance the humidity level in your home will be very high. This is not only uncomfortable but inefficient.

What does 90% forced air heating mean? ›

An AFUE of 90 percent means that 90 percent of the energy is used as heat, and only 10 percent is wasted, usually up the chimney. Older furnaces can have an efficiency as low as 60 to 70 percent.

How hot can a furnace get? ›

When the combustion occurs and air is first heated, the temperature is between 140 degrees F and 170 degrees F. This is extremely warm and could be dangerous to anyone if they got too close to it or it was blown directly into your home.

Is it OK to tape over a vent? ›

You could mess with the air flow.

Just because you cover the vent, it doesn't mean your HVAC system knows that. It will keep pushing air to those vents, and if they're closed, you could cause a buildup of air pressure and insufficient airflow which could damage your system.

Is duct tape over vent a fire hazard? ›

When sealing your dryer vent or attaching it to the wall, duct tape is not the best option. In fact, duct tape can cause serious fire hazards and safety risks.

Why is there a burning smell coming from my vents? ›

Dirty Filter

If your air filter is clogged, these contaminants can get sucked into the blower and cause it to overheat. This can also lead to dirt and dust reaching the heat exchanger and heating up. Both of these will cause a burning smell and can be mostly avoided by changing your filter regularly.

How hot can Gorilla duct tape get? ›

WHAT IS THE TEMPERATURE RANGE FOR GORILLA TAPE? Gorilla Tape should be applied at room temperature. Once applied, Gorilla Tape will hold strong between 0°C to 65.5°C.

Is HVAC duct tape heat resistant? ›

The one thing it can't withstand though is heat and extreme temperature changes. This is one of the many reasons why duct tape should never be used on ducts. Long periods of heat cycling can cause the adhesive in duct tape to break down over time.

Can duct tape catch on fire from heat? ›

Can duct tape catch on fire? The mesh fabric used to make duct tape is flammable, however, it's also coated with polythene which isn't flammable. As rubber isn't flammable either, this means that the glue used on duct tape is also safe from fire.

What steel is best for high heat? ›

Stainless Steel

Stainless steel alloys are known for their resistance to corrosion and heat, which makes them ideal for use in the Aerospace, Automotive and Construction industries as well as specific parts like Pressure Vessels, Steam Turbines, Boilers and Piping systems.

What metal can withstand 6000 degrees? ›

Tantalum carbide (TaC) and hafnium carbide (HfC) are refractory ceramics, meaning they are extraordinarily resistant to heat.

What metal can withstand high heat? ›

Tungsten. Tungsten has the highest melting point of all metals and, at temperatures greater than 1650°C, the highest tensile strength. Its thermal expansion rate is similar to that of borosilicate glass and silicon.

How cool should my house be if it's 100 outside? ›

How cool should my house be if it's 100° outside? The majority of air conditioning units are designed to only cool the air about 20 degrees from the outside temperature. If the temperatures outside are approaching triple digits, you should set your thermostat at about 78°.

What are the signs of an overcharged unit? ›

In summary, there are seven symptoms or telltale signs of a system that has too much refrigerant.
  • High discharge temp.
  • High subcooling in the condenser.
  • High pressures in the condenser.
  • Higher condenser splits.
  • Normal-to-high evaporator pressures.
  • Normal superheats.
  • High compression ratio.
6 Aug 2018

What is the maximum temperature allowed while holding? ›

Foods kept in cold holding must stay at or below 41°F at all times. Foods that fall into the “Danger Zone” must be thrown away. If the temperature of food falls into the “Danger Zone”, throw away the food. Germs grow quickly at these temperatures, making food unsafe to eat.

How hot does a 80% furnace flue pipe get? ›

A properly tuned 80% efficient furnace, that is producing the rated output the manufacture states, should have a flue temp between 300º-400ºf when measured at the equipment. If this temp is met, flue gases should not condense in the flue.

What is the hottest section of the furnace? ›

The bosh is the hottest part of the furnace because of its close proximity to the reaction between air and coke. Molten iron accumulates in the hearth, which has a taphole to draw off the molten iron and, higher up, a slag hole to remove the mixture of impurities and flux.

What temp is too high for a furnace? ›

When you switch over to your HVAC system's heating system, it's usually best to stick to a temperature between 68 to 72 degrees. Start at the lower end, and work your way up until you feel comfortable.

What is excessive temperature rise? ›

Hyperthermia is an abnormally high body temperature — or overheating. It's the opposite of hypothermia, when your body is too cold. Hyperthermia occurs when your body absorbs or generates more heat than it can release. A human's normal body temperature is about 98.6 degrees Fahrenheit.

What is the expected mean temperature rise? ›

Results from a wide range of climate model simulations suggest that our planet's average temperature could be between 2 and 9.7°F (1.1 to 5.4°C) warmer in 2100 than it is today. The main reason for this temperature increase is carbon dioxide and other heat-trapping “greenhouse” gases that human activities produce.

What is a rise temperature? ›

What is temperature rise? Temperature rise is the difference between the average temperature of the transformer windings and the ambient temperature.

How hot does a vent pipe get? ›

Exhaust temperatures from standard efficiency furnaces are usually in the 300-400° F range. The exhaust gases from a standard-efficiency furnace are hot enough to melt a PVC pipe.

How hot can duct insulation get? ›

Fibrous glass duct wrap insulation is designed for application to the exteriors of commercial and residential sheet metal heating, ventilating, and air-conditioning ducts and plenums operating at temperatures between 40˚F (4˚C) and 250˚F (121˚C).

Does reducing duct size increase pressure? ›

If your ducts are too small to accommodate the air flowing through them, the pressure increases and backs up in the system. This causes resistance for the blower fan, reducing your HVAC system's efficiency and longevity.

How high is too high for heat in winter? ›

Generally speaking, the best temperature to set the thermostat in winter is between 68 and 72 degrees. But when you are away from home, you can get away with keeping your home between 62 and 66 degrees. One way to find the best temperature for your family is through trial and error.

What happens when heating rate is too great? ›

If the heating rate was too high, the measured value would exceed the hemispherical temperature, resulting in an elevated melting point. This phenomenon was generally called the “hysteresis” of the melting point detection, and the larger the heating rate was, the more obvious this hysteresis performance.

How long can you survive in 120 degree heat? ›

Given enough water and access to shade to avoid sunstroke, humans can survive for several hours in dry heat, up to temperatures in the 120s.

Will a heat pump work at 90 degrees? ›

Heat Pump Cooling Efficiency

While heat pumps can work in hot weather, the hotter it gets, the less efficient they may become. When it's 90 degrees Fahrenheit outside or more, it may take a heat pump several hours to bring the indoor ambient temperature down to a comfortable 70 degrees.

At what temperature do heat pumps become ineffective? ›

Heat pumps do not operate as efficiently when temperatures drop to between 25 and 40 degrees Fahrenheit for most systems. A heat pump works best when the temperature is above 40. Once outdoor temperatures drop to 40 degrees, heat pumps start losing efficiency, and they consume more energy to do their jobs.

At what temperature does a heat pump kick in? ›

It is important to note that the vast majority of air-source heat pumps have a minimum operating temperature, below which they are unable to operate. For newer models, this can range from between -15°C to -25°C.

How hot can galvanized steel get before it melts? ›

Melting Points

One of the main ingredients in the mix of galvanized steel is zinc. Zinc coating melts around 900 ˚F and vaporizes at about 1650˚F. The zinc that is near the weld does not even hold up, it actually gets vaporized. Regular steel has a melting point of approximately 2,750˚F.

Does galvanized steel give off toxic fumes when heated? ›

Galvanizing usually means coating mild steel with zinc. Zinc, when vaporized, which it does easily, when subjected to high heat, is very toxic if inhaled.

Is galvanized pipe heat resistant? ›

Experts agree that the maximum ambient temperature for maintaining structural integrity of HDG steel is 392° F, or 200°. C. If HDG steel is heated to temperatures above 392°. F, its outer layer of zinc begins to peel off.

Will fire burn off galvanized coating? ›

The short answer is: Yes.

What temperature will weaken steel? ›

Temperatures need not be extremely high to begin to lower the properties of the steel. Some of the very hard wear plates found in industrial applications (near diamond hard) will begin to soften at 280° to 350°F.

How hot does metal have to be to warp? ›

Even the lowest grades of steel, which by the way are not used in residences or other buildings do not commence to warp till 150-200 degrees C or 300-400 degrees F, a lot warmer than sunlight could warm them.

Can stainless steel withstand high heat? ›

Although the duplex stainless steels have good oxidation resistance due to their high chromium contents, they suffer from embrittlement if exposed to temperatures above about 350°C, so they are restricted to applications below this.

Why do welders drink milk after welding? ›

The milk theory is based on the belief that when welders drink milk, the calcium in the milk will “saturate the body” and prevent the body from absorbing toxic heavy metals that can be found in welding fumes, such as cadmium.

What are some signs of galvanize poisoning? ›

Galvanize Poisoning

A moderate case of exposure will result in symptoms including chills, shaking, a slight fever, vomiting and cold sweats. If you begin to experience any of these symptoms you should immediately stop working and get some fresh air.

What is welders flu? ›

The metal fume fever (MFF) is an inhalation fever syndrome in welders of galvanized steel, who join and cut metal parts using flame or electric arc and other sources of heat. Inhalation of certain freshly formed metal oxides produced from welding process can cause MFF as an acute self-limiting flulike illness.

Which type of pipe can withstand the highest temperatures? ›

CPVC can handle temperatures up to 200° Fahrenheit, while PVC peaks at 140° Fahrenheit. Above those temperatures, both CPVC and PVC will begin to soften, increasing the risk of joints and pipes failing, and therefore, failing of the plumbing system.

What pipe can withstand heat? ›

CPVC, though similar to PVC in name and available product types, exhibits superior resistance to heat and pressure, which enables it to be used in more demanding industrial applications.

What metal can resist the most heat? ›

Researchers have discovered that tantalum carbide and hafnium carbide materials can withstand scorching temperatures of nearly 4000 degrees Celsius. These materials may enable spacecraft to withstand the extreme heat generated from leaving and re-entering the atmosphere.

Is chicken wire flammable? ›

Fire Hazard: Not flammable.

What do you extinguish a metal fire with? ›

In the event of a fire, types A, B, and C fire extinguishing agents will react with combustible metals. Therefore, unique agents such as potassium and sodium are used in type D fire extinguishers to put out fires with combustible metals. Type D fire extinguishers are yellow and have a five pointed star on them.

Can I use a metal bucket as a fire pit? ›

You will begin by drilling holes in the sides of your galvanized bucket, then add the screws. Then, you will set your grill inside, then you can put the fire pit in place, and start your fire. This is such an easy DIY, I really love it!


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