Noisy Tankless Hot Water Heater

Prozze

I have a gas recirculating Rinnai Tankless Hot Water Heater, model# RSC199IN. Upon normal start-up, the fan and heating unit produce a loud low frequency drone sound and vibration from the unit. Since the unit is mounted in the garage on the other side of the kitchen wall, the loud sound and vibration carry into the kitchen and living area. It seems this is a known problem and there are bushings available to mount between the unit and the sheetrock/wall studs to buffer the vibration and noise. Does anyone know if these bushings are available and if so the product and source for purchasing? Thank you for your consideration.

HVACNUT

Vibration mountings aren't going to get rid of the droning sounds. I'd be more concerned with that.
How old is the water heater? When was the last time it was serviced? Is there a combustion report from the last service?

Mad Dog_2

Could be Air-gas mixture is off.  Mad Dog 🐕 

Prozze

In response to HVACNUT: the water heater is brand new and was just installed. I'm going to try adding bushings to the mounting of the unit and a sound abatement panel on the wall behind the unit.

Prozze

By the way, it's replacing a Rinnai RUR98iN which was a recirculating 9.6 gallon and this one is a 11.5 gallon so is a bit larger. The plumber doesn't find anything unusual about the unit and the noise. The problem is that it's mounted on 2x4 across the studs in the garage on the other side of the kitchen wall and the sounds carries into the kitchen and living area.

Larry Weingarten

Hi, Any chance a framework that sits on the floor could be made to attach the heater to? If the heater is behaving normally, I'd look for a way to decouple it from the framing.
Yours, Larry

Prozze

Hey Larry, that's a thought and I've been thinking about it. The garage floor is concrete so I'd have to come up with some way to pull the unit off the wall and affix the framework to the floor. Then of course I'd have to move the unit off the wall and make some plumbing changes...more cost added:-( I got some bushings and washers along with a sound abatement panel and will give it a shot and go from there.

HVACNUT

Prozze said:

In response to HVACNUT: the water heater is brand new and was just installed. I'm going to try adding bushings to the mounting of the unit and a sound abatement panel on the wall behind the unit.

That's all fine and good, but the new installation should've come with a combustion report. 

Prozze

HVACNUT, what does the combustion report tell me? How would I use it?

Stet

I do not see why there should be any type of droning noise. Why was the unit replaced?
Was circulation pump replaced also? I have had these make a droning noise if the circulation was not good.
Is there a buffer tank on this system?

Lance

Its new? Did you try contacting Rinnai tech support? You just may have a bad part, or perhaps another issue. Be in front of the unit, take a pic or record of sound and they will tell you if you have a problem that is warrantied or not. You should not have that type of sound when its running. Noises are tricky sometimes to diagnose. From gas flow in corrugated pipe to velocity in water pipes. I am a Rinnai trained service tech and I will tell you, you must read and follow their manual completely. Do not assume anything. I once saw a 38GPM pump installed for recirc when a 4 GPM should have been specified. It had to be replaced. A circuit board failure, a sensor failure, a bad fan bearing, a throttling problem on the burner gas air system. All can be suspect. At least register it and if there is a recall or it gets worst, it will be documented to support your warranty claim. Good luck. Bushings are not the answer. Ear plugs might work.

rick in Alaska

When ever I have a had a problem with a Rinnai making a vibration noise, which I am not sure you have, it was moths in the air fan causing an imbalance. You might verify that nothing got in to the fan.
Rick

Intplm.

Prozze said:

By the way, it's replacing a Rinnai RUR98iN which was a recirculating 9.6 gallon and this one is a 11.5 gallon so is a bit larger. The plumber doesn't find anything unusual about the unit and the noise. The problem is that it's mounted on 2x4 across the studs in the garage on the other side of the kitchen wall and the sounds carries into the kitchen and living area.

Some things I have found that can cause the issue you are having are:

The gas supply is inadequate. (It's a larger unit? Correct?)
Water pressure is low.
Water volume is low.
Fan obstruction.
Debris in the exhaust.
The dip switches are incorrect, for example...Lp gas but switched to Natural gas or vice versa.

Is the unit showing any error codes?

It should not be vibrating at all. Did the older one make this noise?
Adding vibration stabilization of some kind may help with the noise but it will not correct the issue happening in the unit.

Rinnai Tech support number 888-746-6347 is a good place to start.

SummitMechanic

There is no way to properly diagnose this without a combustion analysis to ensure your fuel/air ratio is set to the proper mixture. That's what the problem sounds like to me, however if it is in fact adjusted correctly, and the noise is not coming from the combustion chamber itself, I would predict some sort of flow harmonic situation is occurring which is usually fixed by flushing any debris out of the heat exchanger, or ensuring the orifice on your gas valve is correct for your elevation.