# Hot Water Storage Tank and Boiler



## SewerRatz

Well I had a call over the holiday where a storage tank sprung a leak. They have a A.O. Smith Burkay Boiler with a storage tank. I thought it was plumbed in a little weird, so when I looked it up on the A.O. Smith site my suspensions where part right.

The way its plumbed in is the hot out from the boiler goes into the top lower fitting of the storage tank. but the recirculation pump is on this hot side moving the water from the boiler to the tank, and just after the pump is the cold water supply.

The way A.O. Smith drawings show it is still with the cold water supply teeing into the hot feed from the boiler, but the pump is on the bottom piping of the storage tank moving the water to the boiler.

My question is the way they have it now is it right? The system been working like this for 30 years. Below diagrams is as follows. First one is how A.O Smith drawn it and the second is how its currently plumbed and how it has been plumbed for 30 years.

Another drawing I came across is showing the cold water supply coming into a tee right at the bottom fitting of the storage of tank which is a tee, then the circulator to the boiler. Then the boiler return to the top fittings at the bottom of the tank.

So a little input from you pro's would be appreciated. Thanks in advance.


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## SewerRatz

Here is the other drawing I found and its by A.O. Smith as well.


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## 1703

I've done a couple of these in nursing homes and the ao smith diagram is how I do them. Mostly cuz if there is an issue, the ao smith rep looks for any excuse to blame it on.

So if I understand what u have correctly, the cold feed will go into the storage tank when the pump isn't running correct?


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## SewerRatz

Colgar said:


> I've done a couple of these in nursing homes and the ao smith diagram is how I do them. Mostly cuz if there is an issue, the ao smith rep looks for any excuse to blame it on.
> 
> So if I understand what u have correctly, the cold feed will go into the storage tank when the pump isn't running correct?


Yep, thats how its laid out. This drawing below is how it is plumbed in when I got there and still plumbed in the same after I replaced the tank.









Now both of these drawings below are from A.O. SMith's site. The first drawing is from their piping diagram database. The second drawing is from a Burkay spec sheet. The difrance from the first drawing and the way its currntly installed is the location of the pump. Instead of pushing water into the boiler its pushing the water into the strorage tank.


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## plumber666

Personally, I'd go with the AO smith drwg with the pump pulling out of the boiler and pushing into the tank, but I don't like the location of the water makeup and expansion tank. I've always put them on the inlet side of the pump. With the makeup on the pump outlet, and usually factory preset to 12-15 psi, sometimes you have trouble moving water in upper stories or at the end of the line in systems with a lot of friction loss, IMHO


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## SewerRatz

plumber666 said:


> Personally, I'd go with the AO smith drwg with the pump pulling out of the boiler and pushing into the tank, but I don't like the location of the water makeup and expansion tank. I've always put them on the inlet side of the pump. With the makeup on the pump outlet, and usually factory preset to 12-15 psi, sometimes you have trouble moving water in upper stories or at the end of the line in systems with a lot of friction loss, IMHO


Thanks for the input. This set up is a single story building restaurant. It does not heat the building just domestic hot water supply to the kitchen.


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## 6th Density

SewerRatz said:


> Here is the other drawing I found and its by A.O. Smith as well.



This drawing makes more sense. However, I would add a swing check valve where that arrow points "Tee should be as close as possible to tank."
I would also make sure I had a vacuum relief valve located "above" the tank on the cold supply followed along with another swing check valve and expansion tank before i even hit that first "mixed water" tee. And of course, add ball valves and unions where you feel necessary as if you'd be the one having to service the system components.

JMHO!


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## 6th Density

The only way I like the first setup is if there was a circulation loop for the entire hot water distribution system.

http://www.hotwater.com/lit/piping/dg/AOSDG61002.pdf


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## 6th Density

I did find one code here in Florida that forces you to connect to the cold water inlet of a "water heater" (doesn't say storage tank), but only if you have a mixing valve.

"607.2.3 Recirculating pump. Where a thermostatic mixing valve is used in a system with a hot water recirculating pump, the hot water or tempered water return line shall be routed to the cold water inlet pipe of the 'water heater' and the cold water inlet pipe or the hot water return connection of the thermostatic mixing valve."


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## ironandfire

IMO the way it's done doesn't seem efficient to me. (cold supply placement) The last drawing would work well, inlet temperature being buffered by the heating loop (low). Pushing through, in this instance, would be better on this one.
Oh yea, I'd throw a check on that low heating loop between the tank and cold supply.


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## 1703

6th Density said:


> This drawing makes more sense. However, I would add a swing check valve where that arrow points "Tee should be as close as possible to tank."
> I would also make sure I had a vacuum relief valve located "above" the tank on the cold supply followed along with another swing check valve and expansion tank before i even hit that first "mixed water" tee. And of course, add ball valves and unions where you feel necessary as if you'd be the one having to service the system components.
> 
> JMHO!


 
If you mean a check between the tank and the tee, you can't as the water needs to be able to flow both ways.

If you mean on the inlet side of that tee, I might buy that.


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## 6th Density

Colgar said:


> If you mean a check between the tank and the tee, you can't as the water needs to be able to flow both ways.
> 
> If you mean on the inlet side of that tee, I might buy that.


Are you saying for the sake of a bypass? Why? It's a storage tank.
Don't forget, I'm here to learn more than anything else, by no means am I an expert.


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## 1703

6th Density said:


> Are you saying for the sake of a bypass? Why? It's a storage tank.
> Don't forget, I'm here to learn more than anything else, by no means am I an expert.


With the system full of hot water and the aquastat on the storage tank satisfied, cold water that is drawn into the system goes into the storage tank via that tee/bottom tapping and hot water exits the storage tank.

When the aquastat on the storage tank calls for heat, the pump turns on and then the boiler turns on. This will make the flow OUT of the storage tank through that bottom tapping, to the boiler and returned to the storage tank via the top tapping.

Think of the storage tank as a regular gas fired water heater, but instead of using fire to heat the water, it uses water that is heated by the boiler.

Clear as mud? 

I'm not very good at explaining stuff like this. Hope it helps.


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## Protech

I would think the cold water inlet should have it's own port on the tank so as to not dilute the heated water return coming from the boiler.

If the cold inlet has it's own port, and the heated water has it's own return port, the heated water will be able to stratify properly.

If the cold line ties into the boiler return line as in the first 2 drawings, won't teh heated water me mixed woth cold water during hot water consumption at the fixtures? This would make for luke warm water entering the tank and cause premature temperature fluctuation at the fixtures I would think.

My $.02


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## 1703

Protech said:


> If the cold line ties into the boiler return line as in the first 2 drawings, won't teh heated water me mixed woth cold water during hot water consumption at the fixtures? This would make for luke warm water entering the tank and cause premature temperature fluctuation at the fixtures I would think.
> 
> My $.02


Nope. The storage tank acts just like a regular tank type water heater- cold in the bottom, hot out the top.

When the mixing of the hot and cold at the bottom of the storage tank occurs (lowering the water temp) the aquastat calls for the pump to start and the boiler gets powered up.


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## 6th Density

Colgar said:


> Nope. The storage tank acts just like a regular tank type water heater- cold in the bottom, hot out the top.
> 
> When the mixing of the hot and cold at the bottom of the storage tank occurs (lowering the water temp) the aquastat calls for the pump to start and the boiler gets powered up.



Thanks Colgar! That makes complete sense now! I totally missed the practicality of it all. This little circ. loop isn't going to be running 24-7. It's only going to be running as demand and heat loss requires it to. The cold water pressure from the bottom is the only force pushing the hot water out the top even if the circ heat loop is not fired up. Who's to say that the boiler or circ. pump can even allow water to flow through it if it's offline. Why take the chance of not knowing.
I guess it just natural to want to try and separate the hot and cold as best/efficient as possible, but that doesn't make it right.
If I might add then, I would definitely add a heat trap to this system right before the first tee at the cold water supply.


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## Protech

I think you misunderstood what I was trying to say. Let me clarify.

Tanked water heaters separate the cold and hot water into a thermocline. An ideal thermocline has a sharply defined border between the hot and cold layers. 

If cold water is teed into the boiler return line as shown in the first photo, the hot water returning to the tank will become warm water when water is drawn out of the tank. This will be due to the mixing of the incoming cold water and the returned hot water from the boiler under high velocity in that section of common pipe entering the tank. As a result, you end up with a thermocline that has hot on the top and warm on the bottom (instead of cold). As the boundary layer rises in higher demand draw offs, it will rise to the top of the tank faster than normal because the hot water never stratified into the upper layer at full temperature. You will end up with a temperature gradient instead of a clearly defined hot and cold thermocline.

That was my point. Will it work? Yes. Will it be ideal? No.

That is all











Colgar said:


> Nope. The storage tank acts just like a regular tank type water heater- cold in the bottom, hot out the top.
> 
> When the mixing of the hot and cold at the bottom of the storage tank occurs (lowering the water temp) the aquastat calls for the pump to start and the boiler gets powered up.


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## 1703

Protech said:


> I think you misunderstood what I was trying to say. Let me clarify.
> 
> Tanked water heaters separate the cold and hot water into a thermocline. An ideal thermocline has a sharply defined border between the hot and cold layers.
> 
> If cold water is teed into the boiler return line as shown in the first photo, the hot water returning to the tank will become warm water when water is drawn out of the tank. This will be due to the mixing of the incoming cold water and the returned hot water from the boiler under high velocity in that section of common pipe entering the tank. As a result, you end up with a thermocline that has hot on the top and warm on the bottom (instead of cold). As the boundary layer rises in higher demand draw offs, it will rise to the top of the tank faster than normal because the hot water never stratified into the upper layer at full temperature. You will end up with a temperature gradient instead of a clearly defined hot and cold thermocline.
> 
> That was my point. Will it work? Yes. Will it be ideal? No.
> 
> That is all


No I understood completely, but.....

The problem is, there is no mixing of the boiler return water (or is it supply?) UNTIL the pump starts (and boiler fires). Until then, cold water enters the bottom of the storage tank just like a plain jane water heater.

Once the pump starts, you'll get the mixing that you speak of. Not really an issue unless the boiler is not sized properly for the load.


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## Plumbus

Unless hot water is being called the system is static and there shouldn't be any significant addition of cold water into the tank. 
I'm surprised that none of the diagrams posted have show a pumped hot water return loop from the various fixtures in the system tied into the cold water supply as in this drawing.
http://www.hotwater.com/lit/piping/dg/AOSDG61000.pdf


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## sfplumber

A few points that I remember having installed many Burkay boilers, and working with a company that was in business for 80 years. 1. install the circulation pump on the inlet of the boiler to keep pump temps down and increase longevity. 2. Install the cold water make up as close to the inlet of the storage take as practical. It should enter the storage to temper the cool/cold make up water. If this enters the heater it could cause condensation to occur (moisture from the flue gases)and this will plug the heat exchanger, causing all kinds of problems. 3. Have the circulation pump run constantly - reliability at the expense of power savings. You will replace fewer couplers, fewer calls for no hot water. 4. Tempurature differential should be around 15 to 20 degrees (boiler inlet and outlet). Higher cold mean an under performing pump or under sized. Lower could mean liming in coils, less heat transfer to water.


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## 6th Density

Much appreciated, SFPlumber.


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