Rinnai Heater Install Question

[Rich Lima]

Hello, I just had a Rinnai RUCS75IN installed in a storage room in the attic / second story of my home. It replaced an original tank heater. In looking at the install, I'm questioning if the he did it correctly. It has two options for venting on the unit. The hole in the middle is currently connected to metal pipe that extends through the roof of the home, about 10 feet long. The second fitting, to the left of the center, also has a metal vent pipe connected to it. It goes up about 4 or 5 feet and stops. To me, this looks like an intake and my guess is that it should also be vented outside to bring in air, not bring in air or worse, discharge directly into the attic space. Does this make sense? Installer said that the second one was there as a secondary vent in case the first one failed for some reason. Doesnt sound right....please help. thanks.

 

[Rich Lima]

also, the air intake is in an attic with cable vents so there is air flow in there.

 

[Sponsor]

 

[Dana]

If the attic room is vented to the outdoors, above the it doesn't really matter that the intake air is coming from the attic space, but if it's a storage room inside the pressure & insulation boundary of the conditioned space it's worth considering correcting that, since it's specifically designed to be drawing air from the outdoors, at outdoor air pressures, and drawing it from a tight room would require providing sufficient makeup air for the 160,000 BTU/hr burner.

According to the manual there are specifications for the minimum separation between intake & exhaust venting terminations to be met which vary depending on their relative elevations. The venting specifications begin on page 7.

If the metal of the exhaust vent is not stainless steel it's a code violation, and is counter to the installation instructions. These are designed to be vented with ULC S636 certified PVC/CPVC, which is tolerant of the flue condensation. There also needs to be a condensate trap and a means of disposing of the condensate.

It looks like a total rookie intallation, and there may be other errors that could be even more problematic, the most likely of which would be undersizing the gas plumbing. The connections to the unit are 3/4", but this has a 160,000 BTU/hr burner, which means if all of the gas plumbing is 3/4" the water heater needs to be less than 20 "equivalent feet" (with the equivalent lenghts of all ells & tees included) between the regulator and the unit, with no other gas appliances branching off from that run. That seems highly unlikely. Most homes need a dedicated 1-1/4" gas plumbing run between the tankless and the regulator to work properly & safely.

 

[Dana]

also, the air intake is in an attic with cable vents so there is air flow in there.

You need a minimum of 160 square inches of free opening in the gable vents (a square inch per 1000 BTU) to have sufficient makeup air for a 160,000 BTU/hr burner from a code compliance perspective. If the gable vents are more than big enough but the room is doored off from the gable vented space, you need to provide a make-up air path between that room and the fully vented space that has at least 160 square inches. This would be minimum of a 12.65" square hole (no grille), or a 14.28" round hole.

Pay attention to the height & location of the gable vents relative to the termination on the exhaust vent to ensure that it complies with the installation manual minimums too.

 

[Rich Lima]

thank you for the responses. Unit is not located in a closed off location and the attic room is vented to the outdoors, I just need to clarify the gable vents are large enough. SO far the unit is working well, minus one instance of the "cold water sandwhich" I've read about. I believe they used the old vent pipe for the gas fumes that was used for the previous gas tank heater. I dont know if its stainless or not, but will look when i get home.

 

[Dana]

The old vent pipe is almost certainly NOT stainless (which is quite expensive), and is guaranteed to fail quickly when used with a condensing appliance. (This is also a code violation.) The less expensive alternative to stainless that is most often used is PVC or CPVC plastic rated for the application.