Need Input on tankless option

[Will Butler]

Hi all,

I've done quite a bit of reading around here and other websites and would welcome feedback. I currently have a 50 gallon hot water tank for a family of 6. Plain and simple we are running out of hot water and are looking at three options. I would really like some feedback on options.

Current Information:
-50 gallon hot water heater
-Current hot water heater 11 years old
-Located in North Texas
-High pressure gas line 1" - From the 1" line it's cut down to 3/4" low pressure lines for all the gas appliances in the house. (see pics attached)
-Less than 10' from high pressure 1" gas line to hot water tank

1) Add another traditional hot water heater and run them together in parallel. I know this will work to nearly double our availability of hot water.

2) Go traditional tankless.

3) Go hybrid tankless.

Option 3 appeals to me most because of the availability to circulate hot water within the house and have instant hot wanter along with possibly endless hot water. Option 2 may work as well, but it appears not all vendors support a recirculation pump. I figure I need around 10-11GPM so two showers and another appliance can run at the same time along with figuring out the cold factor in winter months.

I'm looking at two hybrid vendors currently. Rinnai (RH180) and Westinghouse (WGRGHNG199).

Do I want condensing or non condensing?

Being a total newb at this and trying to learn before I purchase and have something installed that won't work properly, I want to educate myself ahead of time. Feedback is appreciated.

Thanks,

Will

 

[Dana]

Make sure your gas line lengths include the additional "equivalent lengths" of all the ells and tees along the path- it make a real difference. Every ell or tee of 3/4" adds another 0.3-o.8 "equivalent feet"

A 199K burner on a dedicated 3/4" line has to be within ~15 equivalent feet, and the line can't be shared by other appliances. A 91K burner like the Rinnai can take a much longer run.

What are your goals here- never running out of hot water? Having higher flow capacity? Instant hot water?

The WGRGHNG199 has recirculation designed in, but it's not a hybrid. The water volume is miniscule, comparable to other tankless units. Your mid-winter water temps may be too low to get two full-flow showers out of a 199,000 BTU/hr tankless without disruption should somebody start a load of laundry, but it'll be just fine with low-flow showers.

The RH180 has a 40 gallon tank, but a burner ~3x bigger than most standalone water heaters, but only half that of the WGRGHNG199. It's burner is big enough to run one full-flow shower 24/365 but not two, but the recovery time at depletion of the 40 gallons would be pretty quick.

If yours happens to be one of the 17 houses in Texas with a full basement, you can get nearly continous showers out of a standalone 50 gallon gas burner by adding a sufficiently large drainwater heat exchanger downstream of the showers to pre-heat the water going to both the water heater and the showers. A 4" x 48" or 3" x 60" unit or larger (fatter & longer is better). But it only works on a vertical section of drain, with almost no heat exchange if it's mounted horizontally.

The nice thing about this solution is that the additional BTUs don't use any gas- it's just taking heat that you are literally pouring down the drain and returning it to the incoming water stream. It works great for showers, but does nothing for tub-fills, since the drain has to be flowing at the same time as the water is coming in for the heat exchange to take place. (These are pretty common in parts of Canada, where the incoming water is barely above freezing in January/February.)

 

[Sponsor]

 

[Will Butler]

Sorry I didn't get back sooner. Our #1 goal is unlimited hot water. Instant hot water would be a bonus, but not a requirement. I'm not sure what distance I'm supposed to be measuring. The main high pressure line runs approx 38' from the city dropoff to where the pressure is lowered for the other gas runs. The low pressure line to the current hot water heater is about 10'. No basement unfortunately.

 

[Dana]

There relevant distance is from the low-pressure side of the regulator, including the "equivalent length" of every ell & tee and valve along the path.

Unlimited hot water isn't the same as unlimited flow. A tankless solution gives you unlimited hot water, but a well bounded maximum flow rate determined by the burner size.

Replacing a standard 50 gallon tank with a condensing tank that has a ~76,000 BTU/hr burner has enough burner for an unlimited 2gpm shower, but at much higher maximum flow rates.

Bumping up the storage temp to an existing 50 gallon tank and installing a thermostatic mixing valve to keep the water at a safe temperature has about the same max flow rate as a bigger-burner tank, but with increased apparent capacity, but only a modest increase in first-hour gallons after the tank's temp has dropped to ~120F. This is the cheapest and first thing to try. The absolute maximum storage temperature of most standard tanks is about 180F, but the controls shipped on residential units don't usually go that high.

Don't crank the temp to the max before first installing a thermostatic mixing valve or tempering valve limiting the water delivered to your hot water distribution plumbing down to 120F or lower. These will mix cold water and the high-temp water at the tank/distribution plumbing interface. Using a faucet or shower mixer to deliver the lower water temp at the far end is not a code-legal solution, due to the highly increased scald risk.

 

[Will Butler]

I'm willing to try the mixing valve and was actually looking at those. I have another issue in that the hot water tank seems to be colder in the mornings; meaning it's not reheating during the night? Once the first shower is taken in the morning, then it seems to work fine. Any thoughts on what could cause this condition?

 

[Dana]

Part of the cooler AM water may be due to the amount of stratification that takes place overnight, so only the top half of the tank might be fully hot initially. The turbulence of the continuous flow of a 5-10 minute shower induces enough motion & momentum inside the tank that the water keeps mixing a bit, taking hours for the motion to damp out completely. If that's the cause, it should be less obvious once you've raised the storage temp and tempered the output.

 

[Will Butler]

So I'm not going tankless. However, I would like your opinion on the Vertex line of hot water heaters. Seems like it's the best of both worlds? If I don't go Vertex, I'll probably just end up getting a Rheem traditional hot water heater. Something like the XG55T12EC50UO model. Thoughts on this model?

Again, my goal is to not run out of water and/or recover quickly.

 

[Dana]

The Vertex is just another glass lined tank, but with a condensing 76,000 BTU/hr burner, that delivers over 70,000 BTU/hr into the water. That is enough to run a single 2.5 gpm shower 24/365 at N. Texas type incoming water temperatures. Reliability wasn't great in the early years shortly after model release, but it's been out there for something like a decade now, and any of those issues should be fixed by now.

For a few hundred USD more money (~$2100 instead of ~$1800) you can get the 50 gallon version of the Phoenix Light Duty (model PH76-50), "light duty" only as compared to large commercial water heaters. Unlike the Vertex it is all stainless, and should be good for 20+ years in any residential application. (The identical water heater is also sold under a Westinghouse name plate, model #WGR050NG076 ). It too has a 76,000 BTU/hr condensing burner, but unlike the Vertex it modulates, with a 3:1 turn down ratio, which adds up to slightly higher as-used efficiency and effectively zero chance of short-cycling under any use patterns. It's well worth the upcharge if this is your "forever house", maybe not if you're moving out in short years.

A standard 50-55 gallon unit with a 50K burner only delivers 40,000 BTU/hr to the water (the rest goes up the flue), which is not enough to run a 24/7 shower in the middle of winter, even at 2 gpm (unless you have a heat recovery heat exchanger boost). A condensing 76K burner delivers over 70, 000 BTU/hr which is substantially more. A 50 gallon tank with 40K of burner output might be able to cover your needs/desires for pretty much endless hot water, but it's not obvious that it will.

 

[FullySprinklered]

Couple of things to consider after all is said and done.

1. There's no such thing as a free lunch.

2. There's no such thing as a free lunch.

So, take a shower, put your pants on, and go the hell to work.