Upgrade or not to tankless

[Eric Jones]

I am looking to switch over to a tankless water heater but want to learn more, real world info about transitioning from a 30 gal gas traditional to a tankless. I have researched some and know some about flow rate and temp rise desired from input temp to 115 deg f. My situation is that i will be needing to shower a house hold of 8 across two showers. My restrictions are that i
I cannot get a larger traditional style water heater because the closet size is tiny and I already have the largest size possible. Im expecting to have a flow rate of 6 gpm but have not tested my exact flow rate.

Id like to know what a good brand would be for use in north Oklahoma area. I only have natural gas available to use. I would also like to know some common issues to be worried about. Would getting the highest flow rate available (9+ gpm) be best for showering 2 adults 6 kids? Im thinking an hour of hot water constantly in demand. Any thoughts or experiences would be appreciated

 

[Jadnashua]

Those gpm numbers are related to the incoming, cold water being typically 50-degrees. How cold does your winter incoming water get? Mine literally gets to barely above freezing (I've measured it at 33-degrees during a cold snap). Those extra, nearly 20-degrees mean either the output of the tankless system instead of being 115-degrees might now be 95-degrees, which, for most people is not hot enough, or, some of them will slow the flow to maintain the set temperature, which may mean a lousy flow. In the summer, it would work fine.

They do require periodic maintenance or the performance will drop off, sometimes radically. For 8-people, a 30-gallon tank is (IMHO) woefully inadequate unless they are spaced out evenly throughout the day, not a typical pattern where everyone is trying to get ready in the morning.

In some places, they can work well, but not everywhere. You may need to upgrade your gas supply lines and maybe meter, potentially, all the way out to the main to be able to supply all of the needed gas volume.

One option is to run more than one unit, but that would likely more than double the costs and maintenance.

Personally, I'd search for a place to put a larger tank, but it MIGHT work for you. The standby losses of a modern gas WH would probably never cost more than the greater cost for tankless system's greater efficiency plus (significantly more) installed cost with the expected NG costs and efficiency.

 

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[Reach4]

My restrictions are that i
I cannot get a larger traditional style water heater because the closet size is tiny and I already have the largest size possible. Im expecting to have a flow rate of 6 gpm but have not tested my exact flow rate.

That sounds like you are a candidate for a tankless WH. You accept the maintenance and descaling and intolerance to hard water. You will learn your hardness, unless you have a water softener. You will learn your TDH (total dissolved solids). You will read the warranty restrictions information before buying.

The big tankless units will take a lot of natural gas. If you want to get many BTUs/hour through existing pipes, check with your gas company to see if you can get the pressure regulation from the company to get raised from 1/4 PSI to 2 PSI. Then each gas appliance will need a 1/4 PSI regulator near the load. That is not a big deal, I think, compared to putting in bigger gas pipes.

As to what brands are available to you, you will probably want to go with the brand that your installer is experienced with.

 

[Dana]

Based on average mid-winter outdoor temperatures the incoming water temp in Tulsa could run as cool as 40F or so. With 105F out of the showerhead that's a 65F rise. Six gpm is about 3000 pounds an hour, so that would take 3000lbs x 65F =195,000 BTU/hr, which the absolute theoretical limit of what you can get out of a largest-in-residential-class 199KBTU/hr 98% efficiency condensing tankless. You'd have to schedule other hot water draws to not conflict with simultaneous 2 x 3 gpm showers.

But at 115F out and 6gpm it's a 75F rise and 225,000 BTU/hr, which is more than the burner can supply. But nobody showers at 115F- it's a scalding hot temperature.

It's time to bucket-test the actual shower flow volumes against a watch with a second hand, and maybe go shopping for low-flow showerheads if the actual flows are north of 2gpm. With 2 x 2 gpm= 4 gpm of shower you would have at least a little bit of margin, just in case somebody needed to wash their hands or start the dishwasher when both showers are running.

If yours is one of the three houses in Tulsa that has a full basement, if you have at least 5' of vertical drain downstream of the showers, a showering family of 8 would do pretty well with a drainwater heat exchanger. A 4" x 48" or taller unit will return about half or more of the heat going down the drain into the incoming water stream, cutting the firing rate needed for the tankless to support the showers in half, giving you even more margin. It's like adding another big burner to the system, but it's a "burner" that doesn't use any fuel. For a 2 person house hold running one shower less than 20 minutes per day it won't have a very fast financial payback, but for an 8 person household and an hour's worth of showering time the return is pretty good.

The output of the heat exchanger needs to feed both the cold side of the water heater and the cold side of the shower. It's often easiest to just let it feed the cold water distribution to the whole house. Unless it's very tall one (have 10' ceilings in the basement?) the output water temperatures will be tepid- not much warmer than room temperature, but way warmer than the incoming water temperature.

They don't do anything for tub fills, since the drain isn't flowing when you're filling the tub.

The current best-in-class units on both efficiency and low pressure drop at higher flow is the fairly recently released Ecodrain's V1000 series. But Renewability's PowerPipe units (the previous best-in-class) aren't bad.

Recent price reporting on the V1000s showed up on this thread.

 

[Will Rogers Plumbing]

I install Rheem or Navien and I'm in your area. Navien has the best support in Oklahoma and are the most common installed. They have models with recirculation built in (A models) or cheaper models with out (S Models) There early models had a few issues, but last 5 years or so they have been solid as long as they are installed correctly. Navien is South Korean, and they make great product, but the Japanese companies have been around a lot longer. Rheem is made in Japan by Paloma. They are solid units, quiet, and reliable. They do not have recirculation built in, but can be added later.

I don't recommend a 6gpm unit. We get cold water in winter, and the flow on smaller units will disappoint you. IMO the lower flow rate units are for single homeowners or a husband and wife with no kids. You need a bigger unit, you got 8 in your house! Plus the units basically take up the same space, so upfront cost is the only thing you save by going smaller, but you will get worst function with smaller unit. Rheem RTGH-95DVLN-2 or Navien NPE-240A/240S is what you need.

What size gas line do you have?
Do you have a floor drain close for condensation?
Is it a single story home or two? You will need new venting for your tankless, can't use your B-Vent
Do you have room for a Tankless pan? Tulsa requires pans for ALL water heaters, Tank or Tankless

Good luck and if I can help, I'd be glad to!