booster on tankless

Home Depot Employee

I wouldnt say that's entirely true, even with an EF of .95 on an electric tank, you must factor in piping loss.
Those are both factors, but it is the significant reduction of the tankless EF that is firing with no DHW demand, yet maintaining a storage tank, plus circ energy required.

kpc_74

has anyone ever....

put a booster tank on a gas tankless water heater (Noritz, takagi, etc.) and used a bronze circ. to push it through for greater volume/storage? How did it work? What size circ(008 good enough)? I have a job where they really need to rid themselves of 3 atmospheric 40gal (1 brick unlined chimney, 2 oil boilers 3 gas water heaters- 1 leaking others soon to follow) and I am looking at cost effective options. ty,kpc

Unknown

Oops

Had to edit . I didn't see it was a tankless heater . Sorry . I did install a booster tank on a regular gas heater and it worked great .

Al Letellier_21

booster tank

Yes we have, several times. Rinnai suggests this when recirc can't be done with standard piping loop. I use a standard 30 gallon water heater and recirc though the heater..we use a Grundfos recirc system with the thermal tee under the furthest sink. It does take large pump to move the water thru the heat exchanger. Consult manuf. info for right size pump to use.

Marty_9

noritz says that you can on their products,and even provides a plumbing diagram

Marty_9

http://www.noritz.com/u/2a1_n751m_dhw_rec.pdf

kpc_74

thanks...

I got that. looked at Rinniai and takagi too. However what I am looking more at is the circulator.... Is there really 40 ft. of HEad? That is HUGE bronze circ. 008 won't get you very much flow... looks like 2- 0011 in series would be needed. thats $700 bucks.

kpc_74

30 gal electric?

Home Depot Employee

??

Adding a storage tank to a tankless defeats the purpose and benefits of going tankless.

kpc_74

yes and no....

if you have well insulated tank(s) the standby losses are low or none. the tanks buy you the storage that 13's apt need, yet not the price that 3 tankless units would cost... trying to find middle ground.

jimmac

is the bigger problem the initial cost or the chimney's condition? with the mechanical room full of three or four gas fired heaters if iam reading it right and two boilers the savings on fuel will be enough. not possible more of a teledyne unit with a storage tank? might be the most cost effective and guarenteed!but then again i have my own arguments with peoples money! figure your 13 baths,kitchens and what else d/w?or wash/m? or even an indirect(s) off the oil boilers?it is always differnet when your looking at the room though i know.

Larry Weingarten

welllll..

..maybe. It depends on the recirc control. 24 hour recirc can easily triple your water heating bill as it's heating a bunch of not-all-that-well insulated pipe. Add any buried line and it's worse.

Yours, Larry

Jack

Have done many

I represent Rinnai so note the bias. I have done many tankless with storage. While the preference is to do straight tankless sometimes the characteristics of the demand or lay-out of the floorplan preclude that possibility. I do prefer higher burner capacity to more gallons of storage.

In analyzing your pumping demands the GPM X Delta T X 500 = BTU is useful. For a single tankless unit I find a 008 or at most a 009 to be sufficient. Rinnai likes to size for the "max performance" which is the higher head pump. That works fine. Personally, I kinda prefer to back off on that a bit. A 008 will pump a Rinnai at about 4.5-5gpm unless you have a million 90's in there. The 009 closer to 6. Plug some numbers into the formula and see how it works out for you. Your choice on the pump! Systems do work very well with the bigger pumps. It causes no harm to the equipment.

In piping the tank (Aquabooster, for example)I have my own thoughts. Feed your CWS to the bottom of the tank, of course. Pump to the tankless off on the upper of the two low tank penetrations on an Aquabooster. Make sure you return to the top of the tank. Most Aquabooster piping diagrams were done when they were feeding these tanks off a boiler which gave a lower delta t and gradually raised the tank temp. Tankless on the other hand are set to only allow set point temp out of them and will regulate flow to do soozZLHPuh. Therefore every gallon exiting the tankless is ready to go to the building. You can pipe it either into the relief valve opening or the HWS opening before the temp valve. This piping arrangement gives a nice smooth operation of the pump and the tankless units. Returning the tankless outlet water to the lower portion of the tank can influence the A-stat and give varying supply temps to the tankless units which can make them ramp up and down. Give a 20F delta T between the tankless and the a-stat.

A local plumber did a restaurant here in town a bit ago with two Rinnai R75LSI's and an 80 gallon tank. He ran them at 160/140. He said it took him less than 12 minutes from a cold start to pick up the tank to 140.

kpc_75

jack...

thanks.... that is what I was looking for.