Tank less Water Heaters

[Instrument 41]

To the plumbing gurus here I am about to do a restoration on a house. Looking at the tank less water heaters. I know nothing about these but I like the space savings. I have heard they provide hot water quickly but how would it handle shower/dishwasher/ washing machine simultaneously? Any drawbacks, issues, warnings?

[Por_sha911]

Cost is higher. Repairs are outrageous and it can be tough to find someone that will work on one. I was warned that if air gets in it burns out the unit. I live at the highest point in our sub division and every time there is a water main break anywhere near us we get air in the lines for an afternoon.

[unclebilly]

We,vet been running ours on crappy well water for 8 years with no issues. We can have 2 showers going, the dishwasher and laundry on at once and it’s perfect. We feed ours with a cistern and a 3/4 hp jet pump and the rinnai is 26’ higher.

Just do it.

[Instrument 41]

I see that they are sized by flow rate. So is it acceptable to size one for max flow rate??

[Jolly Amaranto]

I installed an electric one in a vacation cabin where there was little space for a tank heater. It automatically shuts off if the flow rate drops below a certain point so that it will not overheat the water. I started out with a low flow, "water saver" shower head. It was found that if too much cold water was turned on, it would back up in the shower head and impede the hot water flow through the coils in the heater causing it to shut off. Things got real cold real quick. With water supplied from a well with a pump and pressure tank, the water pressure would vary from 20 to 40 PSI causing all kinds of challenge maintaining a constant temperature at the shower head. By switching to a higher flow shower head, temperature control improved greatly.

[dad911]

Originally Posted by Instrument 41

I see that they are sized by flow rate. So is it acceptable to size one for max flow rate??

Flow rate, and input water temp. Have one in Florida & NJ. Need less power in Florida, as temp of public water(in fl) is warmer than our well water in NJ.

For example:


In florida, this model will 3 showers (5 gpm) in NJ 2 showers (3.1 gpm)

No problems for us. Florida unit is about 8 years old.

[look 171]

Yep, float rate. Assuming your shower heads and faucets are 2.6GPM. Call mfg and they will get you the right unit. I usually like to go bigger due to tubs in the house. Keep in mind that with a instant hot heater, the hot water will take longer to get to the faucet compare to the traditional tanks. There are ways to wire up a re-circ. pump with a timer and a temp sensor to turn it on and off accordingly. Trick is to flush it yearly and install it with a scale filter and change that yearly. It will save your heater as they can last a long time. I personally like Takagi. Its the Lexus and just works and works. AS far as I know, its still all made in Japan.

[HarryD]

I have mixed feelings about tankless water heaters.

PLUS
-Unlimited hot water
-If installed very close to the point of use, the water is hot right away
-Compact

NEGATIVE
-If someone likes to hang out in the shower, you will spend a lot on hot water. A regular water heater runs out and makes them stop.
-Must be sized to match the demand. If too small you will not have enough hot water. If to large, it will not heat properly.
-If far from the point of use, it can take a while to get the hot water to where you need it just like a tank type heater.

Personally, except for a hand sink in a remote bathroom or lacking adequate space, I would go with a standard tank type water heater.

[dad911]

Plus - No energy unless demanded. Size allows it to be located closer to point of use.

Too large/not heat properly has not been an issue in our experience.

[HarryD]

Originally Posted by dad911

Plus - No energy unless demanded. Size allows it to be located closer to point of use.

Very true and good points

Too large/not heat properly has not been an issue in our experience.

My experience: At work we installed a large tankless unit to help clean equipment and service a bathroom. Over time the equipment went elsewhere leaving only the need to service the one hole bathroom and shower. The unit was unable to provide adequate hot water for the lower flows. When we replaced with a unit sized for the demand, much better.

[look 171]

When we install these things in larger homes, we always like to separate the house in two and put them near the baths or kitchen. Two small ones are more efficient then one large unit. We found that the largest unit only need little flow to get it going. It does require more float then the smaller units.

[Bill Douglas]

Around here Rinnai https://www.rinnai.us/tankless-water-heater/catalog are very popular. I've been in various holiday homes and friend's houses where they are installed and I can't think of anything I don't like about them.

The retailer can tell you the size to use so you don't get temp/flow problems.

[Evans, Marv]

I have two in my house where just the two of us live. Both are Rinnai (sp.?) rated at 6 gpm. The one in the back serves three bathrooms. The one on the other side serves the washer, kitchen, & garage half bath. They're both propane. I considered electric but after finding out one ate up 160 amps at full tilt, I chose gas. Mine are nine + years old. I have a circulating pump for the bathrooms to get hot water there faster. The only down side I've noticed is the delay in getting hot water, but it's a minor thing you get accustomed to. I will confess I've only flushed them once at three years after install. I have a good 80K grain water softening system and had the water tested before & after the softener. The hardness & ph are in good ranges. They serve us well & I'd make that choice again. I think though I should flush them again even though I don't seem to have any trouble with mineral deposits.

[911boost]

I had one installed a few weeks ago so I could get rid of the exhaust flu in order to move a wall and remove the floor to ceiling chase above the old water heater and furnace.

We also installed a recirc line to the master bath and before it would take 3-4 minutes to get hot water, it is instantaneous now. I have a filter in mine and am very happy. It is a Navien.

[pete3799]

I use one to heat my garage floor (radiant heat). It's a Takagi and have had no trouble with it in the 11+ years it's been in service.

[NY65912]

I've got a Navien NPE-240 and it provides endless hot water. 2 showers, whirlpool and 2 kitchen sinks.

As a professional plumber/engineer, I love the fact it is as big as a suit case and super easy to plumb.

I would never go back to a tank.

[flatbutt]

Been using one for 9 years with no problems.

[Nickshu]

My Dad installed a Rinnai in a house he built about 10 years ago. After a couple years he added a small electric water heater, fed by the Rinnai, and a circulating pump that was set on a timer. This pump would circulate hot water (heated first by the Rinnai, then kept warm by the small electric tank heater). During the times he needed hot water at the far end of the house (dinner, shower time, etc) it would circulate hot water so it was available on demand. The Rinnai would only run when the small electric tank heater called up for hot water, so it would not run the tankless all the time. He did have to run a return line or two in the house so the hot water plumbing was a loop for circulation purposes.

I thought this was pretty ingenious. Dad's plumber thought so too and he has installed this setup on several houses in the area since then.

[vash]

the only thing i miss about the house i sold was the fast appreciations in value and my Rinnai water heater. my house was tiny, so that water heater covered it easily. fast hot water, forever. i remember my gas bill went down. it favors the folks that take fast showers. i was lucky back then. i had the option to mount it outside the house, so we bought the exterior model. i miss hearing it turn on when i flip the switch for hotwater.

i am counting the day when my tank heater in my new home fails. i will go tankless for sure. but this time, i will have to suffer the cost of the expensive double wall exhaust stuff, i think. it will be indoors.

i already had my electrician put an GFI-elec outlet near where i guess we can install the thing.

[Deschodt]

Lots of good posts an clever ideas above.... Used to have one in our FL house, did not rush to buy another in CA house... That's not a lack of endorsement but i really depends on application and reasons...

- Our WH was upstairs, if it failed that would have caused a lot of floor/ceiling damage. That was a big reason to go tankless... On new house it's under the house so it can fail and not cause an issue... the price difference is big in favor of a tank too...

- Depends where it's located... our tankless was on the only side of the house where it made sense to connect to gas (otherwise big expense to connect - this was a big house, all blocks, with bathrooms all over the map) - as a result it took a while for hot water to reach its preferred destination, over a minute for sure.. I suppose in the smaller CA house made of papier maché and popsicle sticks, one could route gas closer or reach all piping easier...

- Tankless is endless, good if you have more guests visiting, bad if you're hoping to time out your wife on shower duration. Unless you lose gas or water, then you have nothing... A tank will at least contain some emergency warm water in a no-utility situation

- Running cost: in FL gas was nearly free, and it replaced a $$$ electrical... in CA gas is expensive, I'm almost better off with electric power at my rates (EV car rate plan), so it's less of a savings here than it was there and haven't felt the same urge to cut the electrical bill...

- Hygiene factor: Empty an old water tank on occasion and weep.... The tankless is guaranteed clean "just heated" water... I wouldn't drink from my old tank ;-)

- climate temp diff: In FL water coming in was never that cold. It heated up fast (though it took a long time travelling through the pipes) and was mostly consistent in output temp... in other places there might be temp differences to the inlet winter/summer, and in winter you may have to wait even longer for warm water (wasting water and time), or adjusting the output temp more often (depends on model I guess)

All in all I think the applicability varies greatly on your personal circumstances... they're fine overall...