Tankless with recirc?......(JohnNY)

Ed_26

Taco has recently released a flyer regarding piping an instant water heater with their d'mand system. Could apply in your case.

JohnNY

I've never had to do it!

This is my basic piping strategy.
I'm thinking the electric water heater will do a nice job of both buffering the temperature fluctuation from the tankless and provide a good way to allow for recirculation without having to fire up the 200,000 BTU appliance.
I would use a timer and aquastat on the recirc pump.
This is a 4-story single family home in NYC.

Am I nuts?

Over doing it?

Thanks for your input.

(same pic in two formats)

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A.J.

It doesn't sound nuts

A mixing valve and flow limiter would do wonders for temp. fluctions.

JohnNY

Mixing valve with tankless would likely increase my flow rate necessary to activate my tankless burner, wouldn't it?
Ever tried it? I'd be interested to know.

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Paul_11

I use rinnai's suggested version

John,
You want to be careful with how you set these recirculation loops up. I just finished my first one, but the gas isn't on yet. I used the suggested version from Rinnai. You can get it on their website. Let me know if you can't find it.
I've installed Rinnai's in the past, but on commercial restaurants the cold slug was a problem for the dishwashing machines. I've told the cooling help to turn on the hot water at the triple sink just before they used the dishwasher to get the cold slug out. That worked, but I wanted to do a better job so I'm now using a small electric hwh with a recirulation pump.

Respectfully,

Paul B. Shay
pshay@arealgoodplumber.com
LMP 1307
LMFS 654B
OUR MISSION: TO PROVIDE WORLD CLASS PLUMBING, HEATING, AND SPRINKLER SERVICE TO EACH AND EVERY CLIENT WE SERVE, FAR EXCEEDING THEIR HIGHEST EXPECTATIONS!

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Norm Harvey

Heres a system 2000 diagram, substitute plate exchanger for tankless coil





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Mad Dog!!!!!!!!

Absolutely NOT John

It is what the tankless manufacturers rec'd AND just makes good sense. In a NYC residence, people expect instant gratification...they don't expect to wait for anything - especially the hot water. Mad Dog

JohnNY

Any more input?

Sorry for the self-serving *bump*, but I was hoping for more input. Does anyone know of a better way to do this?

Maybe I'm just looking for validation.

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Mike T., Swampeast MO

Here's an alternative.

Note the addition of two check valves and how the DHW loop goes back only to the tank water heater.

Piped this way, the tank water heater will be the SOLE source of heat for recirculation--just don't forget to disable the recirculation circulator when the instant water heater is running!

That would also work fine under gravity if you return to the drain connection of the tank water heater instead of the normal cold water inlet and the piping layout is suited to gravity recirculation.

Forgot the drawing in the original post. Sorry!

Mike T., Swampeast MO

Here's an alternative.

Note the addition of two check valves and how the DHW loop goes back only to the tank water heater.

Piped this way, the tank water heater will be the SOLE source of heat for recirculation--just don't forget to disable the recirculation circulator when the instant water heater is running!

That would also work fine under gravity if you return to the drain connection of the tank water heater instead of the normal cold water inlet and the piping layout is suited to gravity recirculation.

Dave Yates (GrandPAH)_1

Here's

a drawing I did some time ago. No need to disable the recirc in this application and if just the recirc is added as shown, the warranties are not affected. The hydronic side, on the other hand, can affect a mfgr's warranty. As noted, professional design work is required to ensure a marriage between a tankless and a hydronic system will last withoit marital discord!

Mike T., Swampeast MO

Please bear with me a moment Dave.

The reason I suggested that the DHW recirculation circulator should shut down when the instant heater is running is to prevent flow through the storage tank and possible reduction of DHW supply temperature that cannot be seen by the instant heater. It would also prevent the instant heater from recharging the recirculation heater.

There's no physical reason why the DHW circulator can't run, I'm just weird enough to say that it's worth it to add a relay to prevent such.

Why? Unless ALL of your appliances are "European" meaning they heat their own water--either from "cold" or to the proper degree--the "instant" heater is going to have a rather high setting at least sufficient for "hot" in a clothes washing machine.

In the manner I suggested, you could run the DHW recirculation at a slightly lower temperature than provided by the "instant" heater--say sufficient for hand washing-- without the "instant" heater being forced to recharge the recirculation tank during longer (say a shower) call.

[ADDED] Are those tiny two-gallon tanks still available?

Dave Yates (GrandPAH)_2

no harm, no foul!

Nothing meant by the reference! In the drawing I did for a client, and used later in a moderated BB for FHB, I had been asked to come up with a recirc & hydronic tie-in where no checks (on the recirc loop) could be used.

Ariston had a 2.2-gallon wall-hung model, but it's been a while since I checked. No biggie as the storage volume isn't too much of a factor in smaller 115V models used for recirc.

Jack

Recirc & on-demand

When I intially installed my Rinnai I put it down by the boiler/indirect. Whoever plumbed my house eons ago put the master bath at the end of the hw line...so, I wait, with either the boiler or indirect. Having recently remodeled two of the bathrooms I took the opportunity to move the Rinnai right under the bathrooms and to re-pipe with a manifold system and 1/2" pex to each faucet. Basically I eliminated all the 3/4" hw piping. Shorter pipe runs and less vol equals better comfort, shorter wait and better economy.

My point is that when installing an on-demand wh, check out the whole system/house and do not simply install the on-demand where the old water heater was. Most water heaters/indirects are a slave to the chimney location. My dv Rinnai doesn't need the chimney. Go ahead and bid the original location (A). Go look for the best location for the new on-demand (B). Tell the customer that B may likely cost a bit more to install but will give the best performance, comfort and economy longer term. On new construction this works too as you can reduce the amount of HW piping dramatically, if you can find the "right" location.

We take recirc for granted as a solution, but it wastes a huge amount of energy. Copper pipe is just a piece of fin-tube baseboard without the fin. It is still an excellent hx, and our pipe insulation is not very high R value.

I vote to eliminate recirc whenever possible to get the best out of the on-demand wh.

I represent Rinnai and the jobs I visit are typically undersized gas lines and water heaters installed on the dark side of the moon.

JohnNY

Thank you.

I appreciate the input.
I especially agree with the idea of refiguring the heater location. In all the homes I've been in while traveling in Europe, I've noticed water heaters in the living space as opposed to in the cellars.
We have to change the way we think when we change the materials we use, don't we?

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