Can I use a PVC vent pipe for the exhaust when installing a Rinnai RU Model Series tankless water heater, such as the RU180iP?

When installing a Rinnai RU Model Series tankless water heater, like the RU180iP, it's essential to use the appropriate venting materials and follow the manufacturer's guidelines to ensure safe and efficient operation. Rinnai provides specific recommendations for venting options, and in many cases, PVC (polyvinyl chloride) venting may be suitable for the exhaust. However, there are several factors to consider when using PVC vent pipe for a tankless water heater exhaust:

1. Rinnai Approval:
Check the manufacturer's documentation and installation manual for the specific model, such as the RU180iP, to determine whether PVC venting is approved for that unit. Rinnai may specify the use of PVC, CPVC (chlorinated polyvinyl chloride), or other approved venting materials, depending on the model and installation requirements.
2. Venting Material and Size:
If PVC venting is approved, ensure that you use the correct type and size of PVC pipe as recommended by Rinnai. The diameter of the vent pipe, its thickness (schedule), and its suitability for venting high-efficiency condensing appliances are important factors to consider.
3. Venting Standards and Local Codes:
Comply with local building codes and regulations regarding venting materials and installation. Local codes may have specific requirements for venting materials, clearances, and termination points. Always follow the most stringent code requirements.
4. Proper Installation:
Proper installation is critical for safety and performance. Ensure that the PVC vent pipe is installed correctly, sloped appropriately to allow condensate to drain back into the unit, and securely connected to the tankless water heater and termination point.
5. High-Temperature PVC:
In some cases, high-temperature PVC (HTPVC) or CPVC may be required for venting. These materials can withstand the higher temperatures of the exhaust gases from condensing tankless water heaters. Be sure to use the appropriate type of PVC if required.
6. Condensate Drainage:
Condensing tankless water heaters produce acidic condensate that must be properly drained. Ensure that the venting system incorporates a condensate drain to safely remove this acidic water, as it can corrode standard PVC pipe over time.
7. Venting Length and Termination:
Follow the manufacturer's guidelines for the maximum allowable venting length and termination requirements. The length, configuration, and termination point of the venting system can impact the unit's efficiency and safety.
8. Professional Installation:
It is highly recommended to have a licensed HVAC technician or plumber with experience in tankless water heater installations handle the venting. Professionals are familiar with local codes and manufacturer recommendations, ensuring a safe and compliant installation.
9. Maintenance and Inspection:
Regularly inspect the venting system for signs of damage, blockages, or deterioration. Perform any necessary maintenance tasks as specified in the manufacturer's manual, such as cleaning or descaling, to keep the venting system and the tankless water heater operating efficiently.
10. Warranty Considerations:
Using non-approved venting materials or improper installation can void the manufacturer's warranty. Ensure that your installation choices adhere to Rinnai's guidelines to maintain warranty coverage.

In summary, when installing a Rinnai RU Model Series tankless water heater like the RU180iP, you should consult the manufacturer's documentation and installation manual for specific venting requirements and recommendations. If PVC venting is approved for the unit, it can be a suitable option when installed correctly and in compliance with local codes. However, always prioritize safety, follow the manufacturer's guidelines, and consider professional installation to ensure the tankless water heater operates safely and efficiently.