Venting a Hot Water Heater: What You Should Know

Properly venting your hot water heater is crucial for safety and efficiency. As experts in home plumbing, we want to provide you with a comprehensive guide on everything you need to know about venting a hot water heater.

How Water Heater Venting Works

The venting system on a hot water heater serves a very important purpose – it removes combustion gases and moisture from the water heater and vents them outside. Here’s a quick overview of how it works:

  • When the burner inside your water heater ignites, it produces hot exhaust gases as a byproduct of burning fuel. These gases contain carbon monoxide, which is deadly if allowed to accumulate indoors.
  • The ventilation system provides a pathway for these gases to be carried outside of your home through the chimney or vent pipe. This helps eliminate the risk of carbon monoxide poisoning.
  • As the gases exit through the vent pipe, the lower pressure created inside the pipe draws fresh air into the water heater through a separate intake pipe. This fresh air ensures proper combustion.
  • Moisture is also produced as a byproduct of combustion. The ventilation system removes this moisture to prevent corrosion inside the water heater.

So in summary, the venting system is vital for removing combustion byproducts and allowing your water heater to function safely and efficiently.

Choosing the Right Venting System

There are a few main types of venting systems used for residential water heaters:

Natural Draft Venting

This is the most common type of venting used. It utilizes the natural buoyancy of hot gases to vent through the chimney. No additional mechanical assistance is used.

Direct Venting

This system utilizes a twin pipe design – one pipe to vent combustion gases out and a separate pipe to draw fresh air in. It can vent directly through a sidewall since no chimney is needed.

Power Venting

Uses a fan or vent motor to assist with the exhaust of combustion gases. This aids in proper venting for high-efficiency models.

Condensing Venting

Used for condensing water heaters which produce acidic condensate that requires a corrosion-resistant stainless steel or plastic venting material.

When choosing a venting system, you’ll need to consider the type of water heater, where it’s located, venting codes, and manufacturer requirements. Our experts can help select the right system for your specific needs.

Key Steps for Vent Installation

Proper installation of the venting system is critical. Here are the key steps involved:

Selecting Vent Pipe Material

The most common options include stainless steel, PVC, CPVC, and Polypropylene. Material choice depends on type of water heater and building codes.

Determining Correct Vent Size

Vent size is based on the water heater’s BTU rating. Undersized vents can lead to blockages and backdrafting.

Maintaining Proper Vent Slope

A slight upward slope is required to allow drainage of moisture out through the vent.

Venting Vertically and Avoiding Horizontal Runs

When possible, vent vertically to allow for optimal airflow. Long horizontal vent runs can accumulate moisture and restrict airflow.

Connecting Individual Sections Properly

Choose vent pipe designed with tapered ends for easy twist-locking. Seal joints properly to avoid leakage.

Maintaining Proper Clearances

Follow minimum clearance requirements between vent and combustible materials.

Providing Support Structures

Use wall straps, guy wires, hangers or other means to provide support and prevent sagging.

Terminating the Vent Properly

Terminate the vent at the correct height and distance from openings. Install a proper cap.

Following manufacturer specifications for vent installation is highly recommended to avoid safety hazards.

Venting Safety Tips

It’s critically important that your water heater venting system operate safely. Here are some key tips:

  • Have your vents inspected annually and cleaned if necessary to prevent blockages. Signs of blockage include backdrafting or carbon monoxide leaking into the home.
  • If converting from natural draft to power venting, ensure vent lengths and sizes still meet code. Power vents allow longer vent runs which could be improperly sized.
  • Use venting designed for your specific water heater type only. Do not mix vent components from different manufacturers.
  • Look for signs of corrosion and deterioration on older vents and replace immediately if found.
  • When installing direct vent systems, be extremely careful to properly isolate exhaust and intake pipes. Prevent recirculation of exhaust.
  • Avoid running vent pipes through unattended or infrequently used spaces like garages or crawl spaces.

Following venting safety protocols is the best way to prevent serious hazards like carbon monoxide poisoning, fire hazards or exposure to flue gases. Contact a professional immediately if you have any concerns.

Signs You Need New Venting

If your water heater venting system is outdated, deteriorated or improperly installed, it can seriously impact the safety and efficiency of your water heater. Here are a few key signs you need new venting:

  • Corroded, cracked or damaged venting pipes. This allows dangerous exhaust gases to leak.
  • Evidence of condensate drainage problems like water spots or drips. This can lead to corrosion and blockages.
  • Soot residue around the vent terminal indicating a possible blockage.
  • Rusting or deteriorated vent pipes or chimney flue.
  • Improperly sloped vents that allow condensate buildup and impede drainage.
  • Vent piping that was previously painted, which can flake off and clog the pipes.
  • Excessive moisture collecting in the water heater combustion chamber.
  • Signs of backdrafting like soot inside the burner compartment.
  • Evidence of improper installation that violates code requirements.

Replacing defective venting ensures your water heater performs safely and efficiently. Our professional technicians can inspect your system and recommend venting repairs or replacement if needed.


How often should water heater vents be inspected?

Experts recommend having your water heater vents professionally inspected annually. Routine inspections can identify corrosion, blockages or other issues before they become serious hazards.

Can I run PVC vent pipe inside the house?

PVC pipe should only be run vertically in conditioned indoor spaces when allowed by code. It should never be used in unconditioned attic spaces or other hot areas. Consult a professional before installing.

What causes water heaters to backdraft?

Backdrafting occurs when combustion gases flow back into the home due to a blockage or improper venting. Common causes include nests in the vent pipe, kinked pipes, improper vent sizing or burned out vent motors.

Why does my water heater need ventilation?

Proper ventilation serves the critical functions of removing deadly carbon monoxide gas as well as moisture from the combustion process. It allows your heater to operate safely and efficiently.

How do I know if my water heater needs a power vent?

Power vents are usually required for high-efficiency heaters with lower combustion temperatures. They may also be needed when code requires specific vent lengths or vertical rise. Check manufacturer guidelines.

Can I increase the length of my water heater vent?

Any alterations to venting must be done to code. Improperly lengthening vents can impact proper drafting and venting of gases. Consult an expert before modifying vent length.


Proper installation and maintenance of your water heater’s venting system is one of the most important aspects impacting safety and performance. Our comprehensive guide reviewed key topics like how venting works, choosing vent systems, installing vents correctly, troubleshooting issues, and important safety tips. Be sure to have your venting inspected annually and contact a professional if you have any concerns. Taking steps to ensure your water heater vents properly will provide peace of mind and prevent potential hazards.