Hot Water Storage Tank Piping

sreja

I've gotten such amazing advice and suggestions from HeatingHelp steam pros, I thought i would take my chance and post a question about the mystery domestic hot water system in my building.



First some quick background: This is a 1929, 5 story brick building which is now a 14 unit condo, in Illinois.



The hot water heater is from 1987, works relatively well, is 80gal tank capacity and 199k btu.



It connects to a giant insulated hot water storage (booster?) tank that is about 20 ft away; i'd estimate that at maybe 120 gallons.  (ps. overhead is what looks like a truly huge decommissioned asbestos covered old water tank that has to be 300 gallons or so, which is no longer in service).  have no idea how old the storage tank is.



The 40ft of pipe (20ft in each direction) between the hot water heater and storage tank are insulated.



The storage tank does not have a built in thermostat -- the thermostat and thermostat controller valve (or pump?) is about half way between the tank and the heater, inline with the pipe going from the tank TO the hot water heater.  It is currently set for 175 degrees.



The hot water heater is set for 135, so I'm guessing that the 175 degree thermostat connecting the hot water tank output to the hot water heater isn't actually doing very much, unless i am misunderstanding.



SEE ATTACHED DRAWING.



The hot water in the building actually is fine -- it gets hot enough, we never seem to run out of heat.  Some locations in the building do take 15 minutes to get hot water while others are instant, but i'm guessing there is nothing we can do about that.



So I guess my questions are:

Does this setup from the diagram make sense?  It doesn't look like the piping layouts i see in new booster tank installation guides.

It just seems a bit excessive in terms of capacity and in terms of circulating water 20 feet in each direction between the how water heater and the storage tank.

Does the thermostat setting on the boster-to-heater valve make sense?

I don't think the storage tank has been cleaned in decades -- does it make sense to do so?

If and when the hot water heater or the booster tank FAIL and need replacement, should we consider changing the setup, and maybe just using a larger capacity hot water heater?

Any other thoughts?



Thanks in advance!

icesailor

Hot water storage tank:

I consider that set-up to be piped wrong. The domestic outlet should cone from the storage tank. Let the boiler be as hot as you like. Let the storage tank be the controller.

That's my opinion.

There are other "issues" with it but that's another discussion.

icesailor

Hot water storage tank:

I consider that set-up to be piped wrong. The domestic outlet should cone from the storage tank. Let the boiler be as hot as you like. Let the storage tank be the controller.

That's my opinion.

There are other "issues" with it but that's another discussion.

sreja

re: Hot Water Storage Tank Piping

It is unusual isn't it?



Especially given that thermostatic valve seems to be set at a temperature that the system will never see..



I suppose in a way if that's true it's just simulating one giant shared tank (mixing the booster and main heater tank at all times).. But i'm not sure..



---



This is another one of those cases where i know enough to know this isn't how such a thing is normally piped -- but not enough to tell you why or what the drawback of it is..



Still hoping someone can shed some light on that..

Mark Eatherton

Treat the water heater as a heat source...

If the water heater were a copper fin tube boiler, you would have a check valve in the cold water inlet line between the bottom of the big tank, and the heat source. Cold water would be forced by a check valve to have to go to the large storage tank and drive the hot water out of that tank to the load. When the tank (big) gets cool, as sensed by an immersed aquastat, the pump and heat source wold turn on and move heated water back into the tank.



Not sure if you have enough tappings on the big tank to make this work, or not.



Here's a drawing of how it should be piped. Just consider the gas fired tank you have as the copper fin tube boiler shown. Same difference.



ME

sreja

re: Hot Water Storage Tank Piping

I'm not really follow the details, though i think i understand basically what you are suggesting.



I guess my situation however is still that:



I understand that one wouldn't pipe a new system like this, and that it's probably the way it is because it has evolved this way over time.



But I do not understand what if anything is actually "wrong" about the way it is set up now.  To me the tank to heater valve thermostat being set at 175 is a red flag telling me that something is fishy.. But I couldn't explain what if anything is inefficient or wrong with the current setup.



Im obviously not going to recommend we repipe everything just because it feels wrong -- I need to know what if anything is *actually* wrong/inefficient with this setup -- especially given that we have good hot water supply.



At this point it is as much about curiosity as anything else -- i'm curious why it is piped the way it is and *why* its "wrong", if it is.



Any thoughts on that?

Mark Eatherton

In re-reviewing your drawing....

It is piped OK, but you don't show a pump to move water between the two vessels. The aquastat is controlling what?



If it is controlling a pump between the two tanks, then it is supposed to be acting as a high limit. You would be better served by putting the aquastat into the booster tank to cycle the extraction pump. Otherwise, with it set the way it is, you are wasting electricty keeping the pump running 24/7/365 when in reality, the real time DHW loads are less than 3 hours per day, plus system standby losses.



I assume the heat source has its own control/aquastat.



ME

sreja

re: Hot Water Storage Tank Piping

Thanks for your time Mark.



It appears to me that the storage tank is just a pure dumb tank with NO controls on it of any kind.



What there is however is an old standalone small electrically powered thermostat controlled valve half way (10ft from each) between the line that leads from the tank to the how water heater.    It's possible that this is a pump not just an electrically controlled valve, but if so it is only about 6 inches by 3 inches by 3 inches and piped inline with the pipe, and this is an old thing so i doubt it.  The thermostat on it is set to 175 degrees.

rlaggren

The pump between the HWH and the booster tank

needs to run all the time or the booster tank would stagnate, go cool, but the HWH would never "know" it. Assuming you have all the components in your diagram there is no way for the HWH to sense the temps in the booster tank which has your domestic-in and domestic-out lines. _Maybe_ there could be a thermal siphon active between the two, but it's not something that can be counted on - so the pump runs continuously and makes the booster tank effectively a part of the HWH tank so the HWH aquastat knows when to fire up and make the water hotter. IOW, w/out the pump, there would be no reason for the HWH to ever do anything - except keeps it's own tank warm. There would in effect be two separate tanks which did not exchange any water (except maybe a small thermal siphon). The HWH would have no way of heating the booster tank and no control of the water temps in the booster tank w/out the pump running continuously.



Rufus 

Mark Eatherton

Got pictures????

That would be extremely helpful in determining if its right or in right field :-)



ME

sreja

re: Hot Water Storage Tank Piping

I'll take some photos and post today.



Went down and listened to it this morning and i think it may in fact be a tiny little inline pump there, between the tank and the heater, still chugging away 24/7 for all of these decades..



I also spotted something quite strange -- what appears to me to be an additional "hot water" line leaving the boiler room, taken directly off the line that recirculates between the tank and the hot water heater.  I could be wrong, or it could be the result of some questionable plumbing evolutions that have taken place over time.

sreja

re: ot Water Storage Tank Piping

Ok here are the photos -- it's cramped in there so i labeled things as best as i could.

I also included photos of the mysterious out-to-building line that takes off from the recirculation line.



Note that the hot water heater and booster tank are in opposite corners of the room and that the recirculation pipe from the heater to the booster tank goes across ceiling, while the pip from the booster to the heater travels on wall at waist height.

sreja

re: Hot Water Storage Tank Piping

I should mention one other reason, other than the pure strangeness of this layout, that i am trying to understand this piping, is that there is at least one unit (mine; probably others) where it takes 15 minutes to get hot water in the kitchen (other rooms are fine); i'm starting to wonder if it's not possible that this mystery line being taken off the recirculation line could actually be feeding a few hot water pipes in the building luke warm water from the bottom of the booster tank..

Mark Eatherton

The red thingy with the screw...

Is a pump, and that screw is not an adjustment. It is a vent to make sure there is no air in the can of the pump because the pump is water lubricated.



The mystery take offs are more than likely gravity circulation returns. They assist in getting the hot water up to the furthest points of use. Normally, those would have their own small circulators on it, and their own aquastat.



Based on the way it is piped, the circulator that is moving water between tanks is also most likely moving water between the tanks and the furthest point of use, which then becomes the circulation return for the building.



This means that the pump HAS to run ALL the time,. hence the reason the stat is turned so high.



The hot water line serving your unit that is slow may very well be connected to this return line.



Does the hot water temperature remain consistent while showering or do you constantly have to make adjustments?



Is the hot water faster at certain times of the day compared to others?



ME

sreja

re: Hot Water Storage Tank Piping

makes sense about the pump -- so now we know one inefficiency of the current setup is that that pump has to run 24hrs a day; the booster tank and the main water heater are basically acting like one single giant tank constantly being kept at the water heater thermostat temperature of 135.



now as for the mystery takeoffs being gravity circulation returns.. i'm afraid my ignorance is now showing since i dont understand what that would mean -- can you elaborate what you think they might be? they go across the ceiling and then exit the boiler room.



you asked about the water line that takes a while to get hot. the water is very hot once it gets hot.  but it can litterally take 15-20 minutes to go from room temperature to hot.  it doesnt seem like time of day has much effect on it -- or anything really.



the bathroom seems to get hot water very quickly (less than a minute); once hot the water never gets cool again.. it seems it can keep up the temp forever.

Mark Eatherton

Sounds like your supply line is not circulated.

The circulation return lines are essentially an extension of the hot water mains, and usually start at the furthest end of the hot water supply main.



Your system appears to be an older system, with steam heat, which is pump less. The DHW was probably also originally powered off of the steam boiler, and the hot water was also circulated by gravity.



Gravity for circulation of DHW will work, but you need some means of making sure that entering cold water will not back up into the circulation return main, otherwise the water temperature is all over the place.



I have set up these systems on new homes, using a nickel ($0.05) with a 1/4" hole drilled in it, inserted into the socket of a pipe, so that the water has a natural path of least resistance when it is being drawn. Works like a champ, and use NO electricity for circulation.



ME

sreja

re: Hot Water Storage Tank Piping

I think your idea that the boiler originally may have heated the hot water in the storage thank makes some sense.



Regarding your theory of gravity circulated hot water.. I can't say that i understand it, but i will try to go read up.  I will note that I think i may have seen a check/gate valve (?) in that takeoff pipe which would make sure water only flows in one direction.



Still, i do not see how what's there now can possibly be serving any useful function.. but i shall try to see what i can find on the web.  I just dont see where this luke warm water from the bottom of the boostertank-to-heater line could be going..

sreja

re: Hot Water Storage Tank Piping

OK wait.. maybe i was just demonstrating a key lack of understanding about hot water plumbing.



If all our domestic hot water distribution occurs as a loop.. then things make more sense -- these "takeoff" lines are the returns from the main hot water loop, feeding back into the hot water heater (mixing with the water coming from the bottom of the storage tank).



I guess that makes sense -- if the returning hot water has to go anywhere that seems as good a place for it to go as any.



That wouldn't shed any light on the 15 minute time to get heat at the kitchen sink of course.

rlaggren

Go to the head of the class

Reverse flow in the recirc loop (the return line from the end of your main DHW supply) is quite possible and can cause that kind of problem. Whether that is the sole or main cause of _your_ problem is hard to say from this distance. It's slightly strange (only slightly) that your bathroom and your kitchen receive different hot water service but quite possible.



Putting a working check valve in the recirc loop (from the building) is the obvious solution, however... Depending on the characteristics of the check valve, it might 1) reduce or stop the flow in the recirc loop to the point of being ineffective; 2) Not close tight enough to solve the existing problem, under the relatively minimal draw your KS represents vs. the size of the DHW piping. The fact that your kitchen sink (a relatively small draw) can reverse the flow in the recirc loop means that the pump (and gravity) doesn't flow much water through that loop; ie. the flow in the recirc loop is very small and slow without much "pushing" it. It is also possible that you are pulling some water from the other return loop, as well. You may want to consider installing small pump on the recirc (from the building) line as well as the check valve. Which  of the two branch recirc lines is yours (your pics showed two, right?... No data for that call and it may not matter providing the pump on the main return moves enough water to keep both return branches flowing in the right direction.



Rufus

sreja

re:Hot Water Storage Tank Piping

Thanks for taking the time to look and advise.



Knowing what to look for now, i think there may in fact be a check valve in that mystery line piping, leading further weight to the theory that it's recirculation from the building merging with the recirculation line between storage tank and hot water heater.  Now whether or not the check valve is still functioning i don't know.



You asked which of the two mystery recirculation lines are mine -- to which i have no idea -- i can't even see where one of them is coming from.



I wonder if it could be the case that over the years certain hot water RETURN lines in the building simply got disconnected (or blocked, etc.) from the return circulation loops, while still being fed from the main hot water supply -- resulting in slow hot water delivery to those lines, while those in the recirculation loop would benefit from the speedy hot water.

Mark Eatherton

I see dead pipele...

You have galvanized pipes. They are subject to corrosion and eventual block off/failure. So your scenario is entirely possible.



ME

RDSTEAM

this may help

have a recirculating pump installed on your recirc piping. really good pumps are very inexpensive to constantly run.  have your recirc line tied into your cold to temper it and install that line into your hot leaving the heater. that line should be dumped into the upper tapping on your storage tank. your lower tapping is where your colder water will sit and should be heated first. by having your cold water inlet freely piped into the bottom and the supply for the heater directly above it you could cause your heater to condense. make sure your delta t isnt higher than 20 degrees. pump between heater and tank can run constantly and set aquastat on heater to 140. this will maintain your tank temp at 140 near the bottom which will give you a few more degrees on your outlet.