Dan and fellow wallies

Unknown

Been a while since i posted, guess i just got tired of getting my brains bashed in. I got my unlimited electrical license. I got a question about a tankless 169k btu water heater. I put this in my own house.. Using all 3/ 4 pipe. I am using my old water heater as a storage tank, could this cause a big pressure drop,



PEACE BE WITH YOU MY FRIEND



DAVID C. BROOME

Mark Eatherton

Hey there Sparkie...

Welcome back.



Are you circulating between the heater and the storage tank or are you just using water pressure to move water between the heater and the load?



Welcome back.



ME

Unknown

This content has been removed.

Mark Eatherton

Unless it has some of those anti-thermosi[hon nipples...

I wouldn't think it would cause that much pressure drop. But tankless heaters in and of themselves do have an inherently high pressure drop.



ME

Jamie Hall

I can't imagine

why a tank should cause a pressure drop -- unless there is some kind of strange baffle in there somewhere.  Unless I'm missing something.  Which I've been known to do.



I don't suppose there is a valve in their which is supposed to be open and seems open but isn't all the way?  I found that happening in a system recently -- old globe valve, the kind with the rubber washer, and the rubber washer had come adrift inside the valve.  Cut the flow way down.

icesailor

Tankless, storage tanks and pressure drop:

There is a way to do this that I do all the time but you all here seem to think it is stupid and can't be done. But I do it all the time.

I've never had the opportunity to do it with an instantanious gas tankless water heater but there is no reason I can envision that it wouldn't work. If your goal is to use the storage tank. You feed the storage tank like it was, a water heater with full size 3/4" piping to the cold and hot inlets. The tankless is connected as a sidearm heater.

I know, it doesn't work. I've been doing it for over 30 years and it always works for me. Maybe it won't work for you. It's always worked for anyone that did it my way but it might not work for you.

Recently, a plumber friend had to change a leaking water heater/storage tank I had installed like I do about 20+ years ago. He was going to use an indirect as a replacement but realized it would turn into a two day job. He couldn't understand how my application worked. I explained and drew him drawings. He still couldn't figure it out because he didn't need to re-pipe anything. He asked me to stop by and show him. When he saw how it worked and what he simply had to do, the light went off. This works on any tankless doesn't it. Yup. Sure does.

You can do it with any water heating source. At least I can.

Mark Eatherton

Chris....

I think I've read every post you've written, and I don't remember ANY one calling you or your ideas stupid.



You are more than welcome to express your case here, and if someone disagrees, then that is their right as well. Just like you get to express your dislikes, but we always do it in a civil manner. We don't roll that way.



Now, if you are talking about installing a high head, high GPM pump between the tank and the tankless, then say so. But don't think that everyone here thinks its stupid. And with hydronics, ANYTHING is possible. Maybe not cost effective, and maybe not the best thing in the world to do, but we can do anything with enough pump power and fire power.



Chill out my friend, no one thinks you or your ideas are stupid. State your case and answer the questions. That's all you can do.



ME

Larry Weingarten

So, a question about the old storage tank.

Is it gas or electric?  If electric, you'll have less standby loss (no flue to lose heat all the time).  I like the sidearm heater application as it's a simple, proven way of doing things.  You get the benefits of having a tank (quick hot water, no cold sandwich and ability to do low flow draws) and the recovery rate of the tankless.



So, to David's question; If you plumbed it the way Chris suggests, all domestic flow would only go through the tank-type heater, not both heaters in series.  You could track down where the pressure drop is with a pressure gauge between the tank and tankless heaters and likely one downstream of both. 



This is a civilized place these days.  Your head isn't likely to get bashed much.  :~)



Yours,  Larry

LarryC

Confused Non Professional

Icesailor,

 

I'm trying to understand.  You plumb a "tankless" to a standard water heater as a sidearm heater.  As I am seeing it, using an Electric WH tank, CW comes in at the top, is pushed down to the bottom of the tank thru the internal diptube.  The HW is pulled off of the top via the exit fitting.  The side arm is connected between the bottom drain out port and the upper element port.

 

What flow turns on the tankless heater ?  The only flow I "see" is natural convection when the sidearm turns on.  But when does the sidearm turn on ?

 

When HW is drawn from the tank, CW comes in thru the diptube and can flow either up thru the tank or go thru the high resistance path of the sidearm.  I would expect that almost all of the flow will go up thru the tank.

 

Please explain.  Thanks.

World Plumber

Tankless Water heater

 There is a big pressure drop through the tankless water heaters they need to slow the water down so it will heat up. The 19 I have installed at the camp work great but there is a noticeable pressure difference between the hot and cold water from the same faucet.

Gordan

Not sure what icesailor does...

But I would have the aquastat on the tank turn on a circulator. The circulator pumps through the tankless. Maybe there's a more elegant way to do it, but this seems straight-forward enough.

Mark Eatherton

What I THINK he is doing....

Raypak, Teledyne Laars and others have been doing this for eons. The path during draw is cold water comes into the circuit piping between the heat source and the storage tank. There is a check valve that causes the water to have to go thru the heat source, and then into the bottom of the heated tank. The hot water in the tank then flows to the point of use.



And as you suspect, there is an aquastat or a solid state set point control sensor on the bottom of the storage tank, that upon call will cycle a high head, high GPM pump to move water between the source, and the storage tank. Absolutely NOTHING wrong with this design, other than parasitic cost of the large pump to move water between the two, and the increase surface area stand by loss of the storage tank.



Tankless purist might sneer at the design, because it somewhat defeats the purpose of having a tankless heater, but the standby loss of a well insulate storage tank (Not gas fired with a large hole going directly through the middle of the stored hot water) is so minimal (1/2 degree F/hour) that it is worth it to not have to wait to fill large dump load soaking tubs, and not having to live with the cold water sandwich, as Larry so eloquently pointed out.



But, as I stated above, I THINK this is what Chris is doing. Hopefully I didn't piss him off and he will come back and splain himself... ;-)



Chris, what say ye?



ME

Gordan

The way I was envisioning it...

The circulator would draw from the bottom of the tank and discharge to the top. Then:



- there would be no direct circulation through the heat source; only forced circulation - so, no pressure drop in the path from supply to fixture

- dilution of hot water in the tank would be minimized

- you could select the circ to match the capacity of the tankless - in other words, to provide the gpm for which the tankless can produce the biggest delta T you expect to see - so you don't over-pump (by much) and feed lukewarm water to the top; ideally, a single pass through the tankless would suffice to bring the water to temp

- as mentioned, no cold water sandwich and you've got the added buffer capacity (of untempered hot water at the top) for large draws.



What's my mind's eye missing?