Tankless for each side of new build?

[econjon]

Hi,

I've read a few of the posts on this fourm and seen some of the wise comments Dana has left. I have a feeling this may turn to a non tankless recommendation, but nonetheless I seek advice on my new build.

I have a two story 4000 sf house for a family of 5. On one side there is 2 full baths (1 tub), kitchen, and laundry. The max hot run from water heater to furthest bath is ~ 25', while the remainder fixtures are within 10'.

On the other side of the house, 40' over, I have master bath, jack n jill bath and half bath. The master bath will have a 2 headed shower but no side jets or tub. All fixtures are approx 20' away.

My idea is to put a Rheem RTGH-95DVLN on the Kitchen side and a Rinnai V75IN on the master bath side.

My questions are:
1) Should I opt for one larger unit with a recirculating line (e.g. rheem rtgh-rh11dvln)?
2) If using two units does it make sense to split them strategically, or is there a better idea?
3) Being in san diego, I assume a water softener is desired. Should I put one in for the entire home water supply? Or just the heater?
4) I am generically opposed to tanked water heaters as

• a) we have very erratic schedules and will be gone multiple chunks of day
• b)would like to not chew up the space in the laundry room (my only option)
• c) would like to take use a hot water for long periods of time (eg. long sequential showers)

But given that, is there a better setup I should consider?

 

[Dana]

Are any of those tubs a soaker tub or spa? (If yes, nominal volume =???)

What is the maximum BTU capacity of your gas meter?

What are the flow ratings of the heads on the dual-shower?

Slab on grade foundation?

Regarding the objections to tanks:

• a) we have very erratic schedules and will be gone multiple chunks of day

So? What's the problem with that? Is the concern about standby loss? (They're pretty miniscule for a condensing tank.) Or maybe it's about something I'm not able to conjure...

• b)would like to not chew up the space in the laundry room (my only option)

Fair enough. In a San Diego climate it could conceivably go on a pad outside, but that could have other objections. By the total amount of space taken up by a pair of tankless water heaters is comparable to that of a tank.

• c) would like to take use a hot water for long periods of time (eg. long sequential showers)

At San Diego's temperate wintertime incoming water temperatures a smaller-burner (76,000 BTU/hr or higher) commercial condensing tank water heater would sustain a single 2.5-3 gpm shower 24/365 on the burner capacity alone, and would have lighting quick recovery after a tub fill or between showers compared to a typical 50 gallon atmospheric drafted residential unit. If the tank is sized for the biggest tub in the house it's not a problem until/unless filling multiple bathtubs at the same time.

The flow limitations of a tank is plumbing & water pressure, not burner size, and can fill the tub in half the time of a tankless. That's perhaps not a big deal for a standard ~35 gallon tub fill, but is an issue with soaker tubs & spas. At best a 199K condensing tankless is good for ~7 gpm at tub fill output temps at your wintertime incoming water temps.