Thoughts on hybrid Rinnai RH180?

[Funkatation]

My house currently has 2 40 gallon NG water heaters that are 10 years old. They are losing hot water faster than before and since they are in the attic I'm thinking of proactively replacing them before a leak develops. I am also in process of getting a water softener installed. I have 3.5 baths and a jetted tub with 2 adults and 2 kids. I don't want the expense of a tankless but saw the RH180 installs like a tank water heater. Lowes has them for around a grand which is a bit cheaper than a plumber can get them. So I do t have to deal with changing plumbing I would get 2 of them. Has anyone run these before? Are they much harder to install? My only change I think I'd need to make is get an electrical connection.

 

[Dana]

The RH180 has about a 90,000 BTU/hr burner, or about 3x that of a typical 40 gallon tank, and you may need to upgrade the size of the gas lines to have enough capacity for it to operate correctly, and for TWO of them to operate correctly they would need to have their own dedicated gas supply plumbing (or a super-fat gas- pipe- 2" might do it) rather than daisy-chained with tees off a single gas supply.

Run the numbers on the total "equivalent length" and size of the existing plumbing, see if there's an even remote chance of getting it to work.

^^this is in 1000s of BTU/hr^^

^^^ be sure to add the fitting equivalent lengths to the straight line.^^^

 

[Sponsor]

 

[Funkatation]

Dana,

Thanks for the info!

In their literature it states one benefit is they can use existing 1/2" gas lines. Wondering if this is hogwash? I do have a 1" line coming in to where the existing ones are and then it breaks to 1/2" to each one.

Assuming this works, do you see 2 RH180 being better than one RUR98i?

I live in Central Texas so water temps should be ok for most of year I just worry around Christmas time when family is over and the water coming in is colder whether or not the 1 tankless can keep up. Everyone likes to quote the 9.8 GPM but even if the water is 62 degrees it won't hit that it seems. . Hence the idea of 2 hybrids.

 

[Funkatation]

The plumber that gave me a quote for the RUR tankless unit looked at my gas pipe and said it should be sufficient. I think that unit is 199000 BTU.

 

[Dana]

You'd be surprised how many plumbers look at the 3/4" connection to a tankless and assume that 3/4" gas plumbing is adequate, independent of the length. Measure it, and count every ell & tee between the regulator at the meter and the unit, and add that equivalent footage. Any branches off to other appliances need to be within the first foot or so of the branch to the water heater.

The half-inch gas line spec for big-burner Naviens is only up to about 25 equivalent-feet, not sure what it would be with the RH180, but you might get 50 equivalent feet out of a dedicated 3/4" line. It would have to be an extremely short & direct run to have from the meter/regulator to a attic-mounted water heater to be able to run two of them daisy-chain teed off a single 3/4" gas line. A pair of standard burner 40 gallon units would do just fine tapping off a single 3/4" line, but I would expect a pair of RH180s to interact with one another, potentially shutting down and spitting out error codes if configured that way. I have no direct experience with them though.

Almost every RUR98i installation would require a dedicated 1-1/4" gas line (no tees off to or from other appliances) between the meter and the water heater to run reliably under all conditions, though really short runs can take a dedicated 1".