Is Water Heater Exhaust Pipe Very Hot?

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Is Water Heater Exhaust Pipe Very Hot?

An exhaust pipe is a passage that allows the release of heated air or other gases through the building’s heating, ventilating, and air conditioning (HVAC) system.

This enables indoor air to be reused before escaping the building in a hot or cold process.

HVAC engineers must design and install an appropriate exhaust to balance releasing hot gas into the atmosphere, capturing fresh outside air for use inside, and removing stale interior-air pollutants following local codes.

Yes! The water heater exhaust pipe can become very hot. Water heaters typically use a combustion process to generate heat, and the exhaust gases produced during this process are vented out through the exhaust pipe. These gases can reach high temperatures, so the exhaust pipe can become hot to the touch.

Despite this, there are several reasons why the exhaust pipe may not be hot to the touch.

Some of the possible causes for a hot exhaust pipe include:

  1. A clogged or damaged exhaust stack or vent pipe.
  2. A damaged air filter or dirty air filter grille.
  3. An insufficient ducting system results in low airflow rates.
  4. A damaged return water heater flue assembly or blocked insulation on the return water heater.

In any of these cases, the exhaust pipe may become hot and require further troubleshooting by a qualified technician.

A water heater that is not working correctly due to a malfunctioning pressure relief valve or an unvented combustion process could also cause the exhaust pipe to become hot.

However, this would be different for gas or electric water heaters.

Should The Hot Water Tank Exhaust Pipe Be Hot?

Yes, It’s normal for the exhaust pipe of a hot water tank to be hot. The purpose of the exhaust pipe is to safely remove the combustion gases produced by the water heater’s burner.

These gases are typically hot and must be vented outside to prevent them from building up inside the house.

The hot water tank’s exhaust pipe is designed to handle high temperatures and is often made of metal, such as galvanized steel or aluminum, which can withstand heat.

As a result, it is normal for the exhaust pipe to become hot during the operation of the water heater.

However, if the exhaust pipe becomes extremely hot, it may indicate a problem with your water heater. For example, you cannot touch it with your hand if it’s too hot. It could indicate faultiness in your water heater.

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However, homeowners should also remember that there are other causes for pipes to heat up besides problems with the water heater.

The exhaust pipe of a hot water tank is usually located on the roof of the house and runs from the top down to a vent or chimney.

If there is any damage to this connection, then it could allow exhaust gases to escape from the tank without being vented outside.

How Hot Should A Water Heater Vent Be?

350-degree water heaters should have a minimum of two square feet of ventilation area, while 400-degree models should have ventilation space measuring at least three-square feet.

It’s also important to note that higher-temperature water heater vents must be located 12 inches or farther away from the heater’s combustion gases.

The flue may vary in size, depending on its function; it’s most likely going to be one inch in diameter, with a 6-inch or 8-inch depth, depending on the size of the heater.

The vents vary in shape, depending on the ventilation system used. The flue is either round or rectangular, with the vents positioned at least 3 inches apart to ensure proper gas combustion.

This also prevents too much carbon monoxide from sticking close to the water heater.

One of the most common flue types resembles a chimney, so the vent installation should be as steeply pitched as possible.

Some companies also have opinions on which shape to use and recommend them; another benefit of these vents is that they can help reduce ceiling dust.

Another type of vent that is becoming increasingly popular is the soffit vent, which uses gasket tape to seal the flue in place. Because such vents are used less frequently, fewer tests have been conducted.

However, soffit vents are often favored over chimney vents since they’re easier to install and provide better ventilation.

They are also known as the “dry vent” type of flue because they use gasket tape to seal, preventing moisture from entering.

What Happens If You Block the Water Heater Exhaust?

OutcomeDescriptionHow to Fix
Insufficient Combustion Air-Restricts the flow of combustion air -Can result in incomplete fuel burning and reduced efficiency.-Unblock the exhaust to allow proper airflow and combustion air intake.
Carbon Monoxide Buildup-Incomplete combustion -Release of carbon monoxide (CO), a toxic gas. -Respiratory problems.-Immediately unblock the exhaust, evacuate the area, and seek fresh air -Install carbon monoxide detectors and ensure regular maintenance of the water heater.
Malfunctioning Safety Devices-Causes pressure relief and relief valve malfunction.Unblock the exhaust to restore the proper functioning of safety devices -Contact a professional for inspection and potential replacement of damaged safety devices.
Fire Hazard-Cause the water heater to overheat, leading to a potential fire hazard-Unblock the exhaust and ensure proper ventilation in the area.

-Avoid storing flammable materials near the water heater.
Damage to the Water Heater-Cause the water heater’s components, including the burner, heat exchanger, and other internal parts, to overheat, leading to permanent damage.-Unblock the exhaust to prevent further damage.

-Have the water heater inspected by a professional to assess any potential internal damage.

Can I Use A PVC Pipe for A Water Heater?

No! Using PVC pipe for a water heater is generally not recommended.

PVC (polyvinyl chloride) pipes are commonly used for drain and vent systems but are not designed to handle the high temperatures and pressures associated with water heaters.

The pipes have a lower melting point than other types, such as copper or CPVC (chlorinated polyvinyl chloride) pipes, which are more suitable for hot water applications.

The connections of PVC pipes are made using glues or adhesives that contain toxic chemicals, such as vinyl chloride and acrylonitrile.

Since PVC pipes are not made for hot water applications, the glue used to fasten the joints can have a lower melting point than the pipe itself.

This weakens the pipe and can eventually cause the joints to fail. Also, if you use PVC piping in your hot water system, it may emit a distinct odor when heated.

State plumbing codes do not require using PVC piping in a hot water system.

However, local, state, and federal agencies have stringent product standards for plumbing products, and some of those may specifically disallow the use of PVC pipes as hot water plumbing products.

Residential water heaters are typically installed in basement or crawlspace locations.

Because the surrounding environment’s temperature can influence the water temperature from the water heater, use a metal pipe with a high enough temperature rating for your application.

Also, make sure you purchase an adequate-sized water heater for your household to avoid overworking your water heating system and maintain safe temperatures in all areas of your home.

Can Exhaust Pipe Start Fire?

No, An exhaust pipe in plumbing is not designed to start a fire. The exhaust pipe in plumbing systems is typically used to expel waste gases from a water heater or furnace to the outside of a building.

These gases are usually products of combustion or byproducts of various processes.

Plumbing exhaust pipes are constructed with materials that can withstand high temperatures and are designed to safely transport these gases without causing a fire hazard.

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They boast metallic materials, such as galvanized steel or copper, which have high melting points and can handle the heat from exhaust gases.

Note that while the exhaust pipe itself may not start a fire, there can be potential fire hazards associated with the devices connected to the exhaust system.

For example, a malfunctioning water heater or furnace can produce excessive heat; if it’s located near combustible materials, it can lead to a fire. In such cases, the fire is caused by the malfunctioning equipment, not the exhaust pipe itself.

To ensure safety, following proper installation guidelines and building codes is crucial when setting up plumbing systems and exhaust pipes.

Regular maintenance and inspections of the heating and plumbing equipment are also important for identifying potential issues before they cause a fire.

How Do I Know If My Pipe Is PVC Or CPVC?

ColorWhite or off-whiteYellowish or beige
Maximum TemperatureTypically, up to 140°FTypically, up to 200°F
ApplicationCold water supplyHot and cold-water supply
Chemical ResistanceResistant to most acids and basesBetter resistance to certain chemicals
CostRelatively inexpensiveSlightly more expensive than PVC
Common UsesDrainage, irrigation, cold water supplyHot water supply, residential plumbing.

Can PVC Pipe Get Hot?

Yes, PVC (polyvinyl chloride) pipes can become hot under certain conditions. PVC pipes have a melting point of approximately 176°F (80°C). The PVC material can soften, deform, and melt if exposed to temperatures above this threshold.

PVC pipes can get hot due to several factors, such as:

Hot Water: When hot water flows through PVC pipes, especially at elevated temperatures, the pipes can absorb some of the heat and become hot to the touch.

However, PVC pipes are commonly used to carry hot water in residential plumbing systems without issues.

Unlight: PVC pipes can become hot if exposed to direct sunlight for long. The high temperatures can cause the pipes to expand and restrict water flow.

If a plumbing system is designed with PVC pipes in mind, they should be sufficiently shaded to prevent them from heating up excessively.

Electric Wiring: PVC pipes can also heat up if they are situated near an electrical wire that produces heat. Electrical wires can heat PVC pipes even at ambient temperatures because heat is produced every time electricity flows through a wire.

Chemical Reactions: Certain chemicals can cause PVC pipes to become hot.

One example is chlorine gas, which can react with the chlorine in PVC to form dangerous compounds known as chlorinated solvents, such as dioxins and trihalomethanes.

These compounds have been shown to cause adverse health effects in humans.

Fungi: Fungi in the soil can cause PVC pipes to heat up. While this is a rare phenomenon, it is referred to as thermophilic fungus growth and can be mitigated by installing a protective layer of plastic coating on the pipes.

Does A Bigger Exhaust Increase Fuel Consumption?

Increasing the size of the exhaust system alone is not expected to impact fuel consumption significantly. The size of the exhaust system primarily affects the engine’s ability to expel exhaust gases and can impact engine performance.

However, the effect on fuel consumption is typically minimal.

It’s important to understand that fuel consumption is primarily determined by engine efficiency, vehicle weight, aerodynamics, driving habits, and road conditions.

While a larger exhaust system may slightly alter back pressure and exhaust flow, the impact on fuel consumption is usually negligible compared to these other factors.

There are a few notable exceptions to this. A system with a resonator or muffler can slightly increase fuel consumption because the system adds weight to the vehicle and can reduce power output;

However, these systems must be able to pass sound emission regulations in most areas.

A larger exhaust system made of lightweight material may positively impact fuel consumption since there will be less back pressure and more exhaust flow, resulting in better engine efficiency.

A larger exhaust system may also affect fuel consumption because the vehicle is heavier; however, air resistance affects fuel consumption more than weight alone.

For example, a one-percent decrease in aerodynamic drag can save up to 3% in fuel consumption.

Can I Use PVC For The Water Heater Vent?

No, You cannot use PVC for a water heater vent due to the following reasons:

Temperature Limitations: PVC is not designed to handle the high temperatures a water heater produces.

The combustion gases from the water heater can reach temperatures that exceed the maximum temperature capacity of PVC, causing it to warp, deform, or melt.

Slow Reaction To Temperature Change: PVC is a thermoplastic that cannot change shape quickly as metals when exposed to heat.

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If your pipes are made of PVC and the water heater malfunctions, then the pipes may need to expand or contract quickly enough to keep up with the temperature changes.

This means your water system can be compromised with dangerous hot or cold air pockets in your pipes.

Chemical Reaction: When heated, the chemicals used to make PVC expand, causing it to siphon off water from your pipes. This can cause corrosion and allow air pockets in the pipes, potentially leading to leaks.

Decreased Operating Temperature: Using PVC for a water heater vent pipe would reduce the heat dissipated into the air, which could cause the pipes to overheat.

Code Compliance: Codes for your area may prohibit using PVC for your water heater vent pipe.

What Kind Of Pipe Do You Use To Vent A Water Heater?

When venting a water heater, the type of pipe used depends on the fuel source and the specific requirements of your local building codes. Here are some common options:

1. Metal Vent Pipe: A category III or IV metal vent pipe is typically used for gas-fired water heaters.

These pipes are made of galvanized steel, stainless steel, or aluminum and are designed to safely vent the combustion gases the water heater produces.

The specific type of metal vent pipe required may vary based on factors such as the heater’s input rating and the length of the vent run.

2. Flexible Polyvinyl Chloride Pipe: Plastic flexible polyvinyl chloride pipes are often used for fuel oil-fired water heaters and certain gas-fired water heaters.

These pipes are safe for use inside buildings and can be bent to fit any pipe layout needed. The main advantage of PVC pipes for venting is that they are less expensive than metal vent pipes.

3. Steel Vent Pipe: Steel vent piping is the best option if you’re venting a propane- or natural gas-fired water heater. Because they are made of metal, steel pipes are strong and lightweight.

They can also handle the high and low temperatures the water heater produces.

4. Thermal Plastic Insulating Pipe: Building codes often call for an insulated type of pipe for a flexible plastic pipe used with natural gas-fired water heaters.

Thermal plastic insulation is made from epoxy Resin Thermoplastic Polyolefin (RTPO). It is typically lightweight and temperature-resistant, and it can handle high temperatures.


A PVC water supply pipe can be used for cold potable water, hot potable water, and low-temperature sanitary applications up to 140 °F (60 °C) with proper fittings.

You can construct potable water supply pipes from either a rigid plastic pipe or a rigid copper pipe.


Hi! I I faced many questions from customers about different products, and there was hardly any help on the internet. After learning all the things about these products as a manager the hard way, I decided to start a blog and help other people.

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