Help with storage plumbing

Used to do this for domestic hot water in 30 floor apartments with electric boilers....Parallel can work IF you can balance them (start with "reverse -return" piping) but series systems are a lot easier to monitor and stratify, especially with horizontal tanks.
I like the crawl space idea provided you insulate the walls and the tanks....

I would go from boiler to top of tank 1, then bottom of tank 1 (opposite end) to top of tank 2, then bottom of tank 2 (opposite end) back to boiler.

warno said:

Today I did some measuring and thinking about the whole system. It turns out with a little work I can put my storage tanks vertical in my garage. But it raises a few more questions I would like help with. In order to do vertical tanks I will have to do pressurized storage with my open boiler. Which I know requires a heat exchanger.

So that leads me to my first question. How do I size a heat exchanger to heat storage tanks? Everything I'm reading gives me DHW or radiant floor or snow melt options. But I couldn't find anything to help me get a plate count for heating storage.

The other potential problem with my storage in my garage is the tanks will be about 120 feet one way to my furnace HX and my DHW sidearm. I wanted my DHW to have consistent flow and my furnace HX was going to run with call for heat. So my next questions are, how do I plumb my HX and my sidearm to run like I wanted them to? Could I put manifold in my crawl space then have my pumps pulling from that manifold? Or how is the best way to do this? Is it ok to constantly pump water underground from storage to house to run my sidearm? I'll be running 1" thermopex for my underground lines.

Any help with this new idea would greatly be appreciated.

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This is a hybrid series/ parallel piping with loads and input as a "two pipe" method.

The tank connectors need to be large and short as possible, 2" pipe perhaps. same for the S&R headers off the tank.

The concept is heat from the boiler can go directly to the loads without first heating the tanks. as the load drops and tanks get to temperature heat is drawn from the tanks.

I would still run the DHW on a thermostat, no need to allow DHW to get to 180 of hotter by running continuously.[

Do you have anything planned for return boiler protection? With storage you will have extended time periods of low return temps if you don't have some way to regulate the return temp.

If you use a always on with a side arm for DHW you will be mixing your tank to one temp. Not really what you want with Forced Air exchanger in the system. Probably better to have a flat plate with on demand pumping. When doing that you might want to consider having a small buffer tank near the DHW.

A few difficulties with remote storage and DHW.

1. You don't want to mix main storage tank so circulate on demand is best.

2. DHW you want near instantaneous heat. Pumping on demand will cause a delay, especially on low demand space heating days.

3. Use of small buffer tank and demand style flat plate will require more controls to compare main storage to buffer temps and replenish when needed.

Another option would be to have a DHW coil in the small buffer tank. Make sure your Domestic water is stable quality if you choose this route. Not an option where I live as water is slightly acidic and aggressive if thermo-siphoning through cooper pipes.

IMO any pumping of water from storage, when it is not needed, will end up decreasing the usefulness of storage. It messes up your stratification, and decrease how long you can effectively heat off the storage. I have manifolds, 5 zones each with a zone valve, and one pump (Alpha) that gets started when any of the zone valves open on a call for heat. It pumps slow to maximize stratification - but how slow you can go would depend how much heat your loads need over a certain period of time.

Will you be trying to heat DHW with the sidearm off storage in non-heating seasons?

Yes, any time you have a pressurized system, you need expansion. Amount of water in that system determines how much expansion.

www.flatplatselect.com for a free sizer program
www.amtrol.com for an expansion tank sizer

warno said:

I plugged in some numbers on the HX on came up with this

View attachment 176212

I did a quick test on my boiler. I'm running about 3 gpm through it now with about 150 gallons in the system and I picked up 10 degrees in 7.5 minutes. So could someone smarter than me tell me if my boiler could keep up with 6 gpm?


The expansion tank calculator said I only needed around a 10 gallon tank. That seems really small, but then again in still new to all this.

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If you invest in a steel expansion tank in that size bracket it will have volume of 15 gallons in total-10 for water and 5 for the air cushion and you will be very happy with the five gallon air cushion.

They work perfectly when they are plumbed properly with the airtrol valve which removes the micro bubbles and holds them in the tank forever. Mine is working very well and providing another 10 gallons of water to add to the water mass of the boiler.

You can install a bigger steel expansion tank with no issues and you will be glad you did.


Yes Warno, you will be glad you invested in a steel expansion tank; OH, and you can buy a much larger steel expansion tank and add that much more water-thermal mass to your boiler and your circulators will be quiet and not create water fall sounds in your heating system and you will be glad you did. I did it and I am glad I did it and I wish I had done it 33 years ago.

AND you will never have to worry about the rubber bladder failing as there is no rubber bladder in the steel expansion tank.

my fathers bladder expansion tank failed after five years and caused the boiler to have blow offs until they changed it and it will fail again in five years.

If you can park that expansion tank above the water supply to take advantage of the height to maintain a lower pressure on the system(attic preferred or at ceiling height hung above the tanks in the room where the trap door is all the better otherwise you will have to deal with a bladder tank and air scoop=YUCK = more plumbing

warno said:

Couple more questions,

With the airtrol fitting is an air separator needed or is it simply plumbed into the tank and tied into the system?

probably a dumb question but, where does my pop off valve go in the sealed system? In the expansion tank?

And what happens if I don't put in a big enough expansion tank?

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First question;

The airtrol fitting goes in the bottom of the horizontal steel expansion tank.
The Inline Air separator comes off the top of the boiler and the tapping on the top
of the inline air separator being 3/4" is piped upward to the steel expansion tank.

An IAS can be used with a large commercial air separator but the steel expansion tank
and airtrol valve installed in the lower tapping are much less trouble and have no moving parts.

Your relief valve is installed in the top of the home boiler steam chest nowhere else, and the system pressure
should not be higher than 12 pounds Per Square Inch with the boiler operating.

Your expansion tank is sized based on the size of the interior boiler and heating loop volume.

My 15 gallon expansion tank is more than adequate for my total volume of 54+- gallons which is the boiler volume + the 10 gallons in the expansion tank and the 7 gallons in the heating loop.

If your tanks are fully open to the interior boiler feeding the steel expansion tanks from one IAS you could use 2 15-gallon tanks plumbed in parallel with 2 airtrol valves being plumbed into a common header pipe connected to the two airtrol valves in the base of both tanks.

The B+G folks have sizing charts for expansion tanks.

warno said:

I don't have a boiler in my house. This is all plumbing from my pressurized storage in my garage. My boiler is an open system OWB. I'm charging storage through a plate HX.

So with that said, in what location should my popoff valve go?

Also all the calculators I have found and plugged my numbers into come up with me needing 30-40 gallons of expansion. That doesn't seem like much For 750 gallons at 190 degrees maximum. Could someone double check for me on that size.

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The only place you need and want a pop off valve is the steam chest of the fossil fuel boiler or wood and coal boiler. with an unpressurized boiler you have the expanse of air above the water level.


In the sealed portion of the system:

You need to install the tanks the pair or triple of the steel expansion tanks goes in the highest point in the system by hanging the tanks in garage ceiling using a common header pipe to the two or three steel expansion tanks outfitted with an airtrol valve in each steel expansion tank.

you can simply mount a single circulator for the heating loop above the storage tanks and pull the water up from the tanks and avoid a lot of issues with trapped air bubbles.

Is there any real reason besides expense you cannot run a second DHW insulated pex tubing line from an external DHW coil the garage with a simple watts mixing valve in the home to keep the water at 120 degrees before entering the fixtures???

Its so much easier to run second pair of lines for the domestic hot water in this way in the same trench eliminating all the extra plumbing in the home.

warno said:

So on my pressurized storage I don't need a pop off valve at all?

I'm already running about 90 feet of thermopex to the house from garage and at $11/foot it adds up real fast so a second line underground is out of the question on cost alone. If it comes right down to it I'll just not heat the DHW off the boiler and simply heat the house. Our DHW heater doesnt use alot of gas anyway so if I'm saving money on just heating the house I'd still be happy.

I'm planning on only having 1 expansion tank. If I can't find a used propane tank to suit my needs I'll build a tank to fit. So I only need one airtrol fitting.

Another question here, if I put a fitting dead center of my storage tanks, could I plumb that to the airtrol fitting instead of using an air scoop in the line? Wouldn't any air bubbles that get pushed into my storage tanks from the system go to the top then move into the expansion tank? Or would I still have air bubbles getting into the loop?

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You cannot use and should not use an air scoop along with an airtrol valve and tank as the tank with its air cushion is what
controls the pressure in the heating loop and boiler.

Building a tank is not a good idea or proper plumbing code/legal.

It would be much simpler and safer for you to invest in either a 30 gallon B+G tank and the proper size B+G airtrol fitting for your system. You may find that all you need is the fifteen gallon tank and airtrol valve as your heating loop system is not that
large to begin with and you can use lower temperature water to its advantage as you can only provide so many BTU per gallon of hot water for heating no matter the temperature.

Once you purge the system of air you will have no air bubbles or waterfalls.

Great questions warno. Bob Rohr has given you fantastic advice. I echo all his comments. Make sure you put the DHW circulator on an aquastat. Side arm style heat exchangers are commonly installed with continuously running circulators which destroy the thermal stratification in the buffer tank. Vertical tanks with thermal stratification are critically important for efficient operation.

Here is a link to a general schematic showing one possible location for the expansion tank.

http://www.biothermic.ca/assets/printouts/FHG Typical.pdf