potable hot water expansion tank question

leonz

Greetings fellow board members,

I am going to order a potable hot water expansion tank so I can use the domestic coil on my coal stoker.

Yes, it should have been done 11 years ago but in January I was making many parts runs to town for what the plumbers needed as they did not have everything they needed let alone a pipe threader and black iron pipe.

I have a mixing valve already plumbed into the system from the original installation and I need to know where I should park the expansion tank.

The propane dealer stuck me with a 40 gallon Bradford White propane fired water heater instead of a 30 gallon unit like I wanted saying that they no longer make a 30 gallon tank and they lied to me about that as I found out later Bradford White still made the 30 gallon propane fired water heaters. I need to know what size expansion tank and where I should have the new expansion tank plumbed in.

Hanging it on the wall close to the domestic coil connections would be ideal.

I want to avoid having the fittings and pipe blow apart like they did 11 years ago when they used propress fittings on the domestic coil connections as the fittings blew apart and ran my well dry in the middle of the night making a mess that took 2+ days to dry out.

Would I be out of my tree using 3/4"stainless braided steel washing machine hoses for the hot water connection from the 1/2" domestic coil in the stoker to the expansion tank hung on the wall that would be reconnected to the hot water heater feed from the domestic coil or should I stick with 1/2" k copper pipe and fittings and new bronze male to male connectors at the 1/2 inch NPT domestic coil fittings. My plan is to use a 5 gallon potable hot water expansion tank just out of caution in any case and hang it on the wall and use 3/4" copper to feed the blended/mixed(cooler) hot water to the propane hot water heater.

I never had a bit of trouble with the 3/4 inch external domestic coil that was installed with the hand fired wood and coal boiler I used for 33 years before this. The hot and cold water copper pipe feeding the home from the old connections is all 3/4" copper and I would use 3/4" copper from the expansion tank to the hot water heater.

Thanks much for the help in this matter.

Larry Weingarten

Hi, I'd like to see a schematic of the system, so I could offer up good advice. Normally, on the cold supply to the tank heater is good, but I'm not clear on where the coil is, or any check valves might be. 😉

Yours, Larry

EdTheHeaterMan

One thing to consider is that the water inside a potable-water expansion tank may remain there for a long time. It may never reach a temperature high enough to control microorganisms that can grow in stagnant water at room temperature.

In fact, some manufacturers of potable-water expansion tanks have designed special connection fittings or flow-through designs to reduce stagnation. The idea is that normal water movement past the connection can create some movement in the tank, allowing at least some of the water to be exchanged instead of remaining stagnant.

Using a piece of hose to make the connection, as you suggested, may defeat that feature and create a stagnant dead leg.

Just something to think about.

hot_rod

In Amtrol speak

ST 5 = 50 gallon

ST 8 =80 gallon

ST 12 =120 gallon

Amtrol also has a Venturi type fitting in the tank to encourage “stirring” of the tank, as water moves in or out

Thermal tanks will work on hot or cold, but on the hot side they can hold a cold slug of water. The tank cools after the heater goes iff and may cool to room temperature

leonz

Good morning Mr. Weingarten, Ed the heater man and Hot Rod/Bob

The kaa-4-1 and larger coal stokers use a circular copper coil to create the domestic hot water in thier coal stoker boilers.

I had so much trouble with this boiler in the beginning because of the chinese hydrolevel controls that allowed it to overheat and go to steam.

Replacing those 2 sets of defective controls with the mechanical Honeywell L8124L triple aquastat, Bell and Gossett RB-122-E low water cut off switch and the Marsh Instruments Triple Gauge solved that control problem for me with absolutely no help from keystoker.

I can safely run and have run the stoker at 150 Degrees Fahrenheit Low Limit Temperature; 170 Degrees Fahrenheit High Limit Temperature all winter long with no issues.

In my opinion with my past 22 years of using mining machinery manuals for maintenance my opinion of their installation manuals and drawings are extremely poor based on thier schematics.

Each model stoker boiler should have its own manual with its serial number.

According to the keystoker boiler installation manual on pages 24 and 25 they want you to use 1/2 adapter fittings which I find odd to begin with and the female coil tapping's are 3/4".

I believe 3/4" bronze nipples could be used safely to connect the 3/4 k copper pipe and fittings could be used.

This keystoker requirement required the clown car plumbers I hired to run 1/2 copper to the 3/4 inch copper cold and hot water domestic hot water lines already in place. I will need to buy a new 3/4 mixing valve as I would want to run 3/4 copper in any case replacing what keystoker insisted must be installed.

The Keystoker direct vent boiler manual applies to my boiler except that I do not have a direct vent draft inducer on my stoker.

Pages 5 and 6 of the keystoker manual for direct vent boilers applies to my stoker boiler.

My keystoker KAA-4-1 stoker boiler is not equipped with a direct vent draft inducer, it is piped to my 16 foot tile lined block chimney.

Their schematic drawings with regard to the installation of the PH-5 expansion tank leave a great deal to be desired.

I will do whatever is required and suggested by you all.

keystoker-direct-vent-boiler-k2-k4-k6-with-6-inch-stack.pdf

I have decided not to attach the other keystoker boiler manual to my post to avoid further confusion.

I suggested to the owner of Keystone who is Dan Snow that they should provide the buyers of thier stoker boilers with copies of "CLASSIC HYDRONICS", "PUMPING AWAY and "HOW COME" to the buyers of thier stoker boilers, whether his did this or not I do not know.

As far as I know they still provide the hydrolevel 3250 plus triple aquastat in thier ready to install wiring harnesses.

At the time I returned the defective triple aquastats to the local keystoker dealer keystoker had 66 of these units returned as defective. They bench tested these units and they stated they were not defective.

I sleep very well at night knowing the Honeywell L8124L and Bell & Gossett RB-122-E are protecting my coal stoker boiler during the heating season.

Leon

hot_rod

Ideally the thermal DHW expansion tank would be on the cold feed in this pic. (domestic cold water input) As long as tnere are no check valves between the boiler DHW coil and the expansion tank connection.

No harm in oversizing the thermal expansion tank, the 8 gallon DHW tanks are not so common, so a #5 or #12, 50 or 120 gallon tank size, should be adequate.

Corrugated copper flex lines rarely fail, braided EPDM probably a safe option, although they do have a temperature limit. Another reason to have the tank on the cold inlet, keep it operatig in a cooler temperature water for extended life.

leonz

Hello Bob,

thank you for your comments, they are most welcome. What bugged me about the whole thing is my external domestic hot water coil that was mounted on top of the Switzer CWW 100 had a huge 3/4" copper coil that served us for 33 years before this with no issues.

My initial plan was to use a 5 gallon domestic expansion tank for this new installation attached to the wall with 3/4" K copper pipe and fittings.

I will mount the new 5 gallon tank on the wall and connect it to the cold side of the domestic hot water coil per your suggestion.

Larry Weingarten

Hi, Where is the 40 gallon tank in relation to this? Is the boiler preheating/feeding that tank? Are there any check valves? Can you take some photos of the setup as it is now? I just don't want to give ideas that could be damaging. 🙀

Yours, Larry

leonz

Hello Larry,

The stoker would be preheating the domestic water and mixed with cooler water before it enters the 40 gallon Bradford White propane fire hot water heater.

The new (3 year old) propane fired hot water heater is 12 feet+- away in a direct line from the stoker boilers domestic coil. There are no check valves in the domestic coil but I believe the 40 gallon Bradford White propane fired hot water heater has a check valve in it.

Thanks much,

Leon

I will use my wife's smart phone to take pictures and upload the rats nest of piping I have. I may have already uploaded pictures of this with my previous stoker boiler posts on the forum too.

leonz

Hello Larry and Bob, I have to correct my error, there are two 3/4" flap check valves on the hot(out) and cold(in) lines that fed the old electric water heater which was removed when the first 30 gallon propane fired water heater was installed in 1987.

Perhaps I should just leave well enough alone now that the stoker is working the way it should with the mechanical controls as I sleep very well at night now?

hot_rod

You could always install a "lazy hand" indicator gauge like this to see if you get expansion related pressure increases. It's really the only way to know IF and how much pressure increase you are getting.

Spring checks without some good differential are not a "bubble tight" seal, so some expansion could slip by.

leonz

Hello and good evening to you Bob,

The hot and cold swing check valves have no springs. I am going to assume the check valve in the 3-year-old Bradford White water heater has a spring.

You are right Bob, installing a pressure gauge in a tee with a lazy hand would be a good idea, I have more to think about before changing the piping.

hot_rod

I don’t know that the BW tank would have shipped with any check valves?

It probably has heat trapper nipples which have a rubber flapper, sometimes a plastic ball. The intent is to slow any potential thermosiphon, keep the hot water in the tank. These are not a tight sealing check valve.

They are also the dielectric nipple for the tank connections.

A swing check is intended to be closed and sealed by pressure differential

Think of a sump pump that pumps water out of a pit. When it shuts off, the water flowing back closes and seals the check. So pressure on one side only.

In a hydronic system or domestic recirc, when the circ shuts off, pressure is the same on both sides of the check. So a swing check is not an ideal hydronic check.

leonz

Hello Bob,

I guess I better cut both of those swing checks out as well.

hot_rod

a pic or sketch might help see if there is a reason or need for them. There maybe a reason for a check.

As I understand you are circulating from a tankless coil to a storage tank?

Or is the tank in series with the coil? Water just flows through when a faucet opens?

Anything used for potable needs to be low lead also.

leonz

Good morning Bob,

The domestic coil in the coal stoker would be plumbed in series with the hot water heater again. The swing checks were there to stop ghost flow from the old electric hot water heater that became plugged with colloidal clay before it was replaced with the first 30 gallon Bradford White propane fired hot water heater.

I sent an e-mail to the keystoker people asking for well defined pictures of the domestic coil and the potable hot water expansion tank as the drawings they have in thier installation/owners manual are extremely poor; so I am waiting on them now.

Finding that the coal stoker was not level from the hopper to the flue breech was very disappointing as they did not shim the boiler with enough shims and only adds to the work I need to do, the concrete slab is level.

Larry Weingarten

Hi, I'd be looking at putting the expansion tank on the cold feed to the water heater tank, after the pre-heater and any check valve. This way, thermal expansion pressure can make it's way to the X tank and it wont mess with hot water delivery. Clear as mud?

Yours, Larry

hot_rod

Is this what you have? No circulator puymp, just flow through the coil to the tank?

With a boiler tankless coil it is wise to have a thermostatic mix valve. AngleMix 520 is an excellent valve for tankless water heaters or coils.

The tank most likely has a heat trap nipple on the hot discharge, no need to add another check

leonz

Thank you Bob and Larry,

Both of you have explained it in great detail for me. I learned today that the domestic hot water coil is a 1/2 inch copper coil; I originally thought that they used a reducer bushing in the coil plate but that is not the case.

The coal stokers domestic hot water coil depends strictly on the water pressure in my wells storage tank system to move cold water through the domestic hot water coil using 20 PSIG low and 40 PSIG high limit only.

They also told me that the cold water feed is the longer tube in the coil and to double check by inserting a pencil in the coil to make sure which side is which.

I have a thermostatic mixing valve in the piping when they installed the boiler 11 years ago.

I will place the 5 gallon expansion tank on the cold water side of the coil when I have the tank bracket attached to the wall near the boiler as you both have suggested. I am waiting on pictures of the coals stokers plumbing with the domestic hot water coil now.

Thank you both very much for the help. All I have to do is start saving a little money for the pipe, fittings and the expansion tank.

Larry and Bob thanks for explaining how putting the expansion tank on the cold water feed side of the coil would work as the hot domestic water expands and can expand through the coil back to the bladder tank and not cause any burst pipe issues.

Respectfully,

Leon