New Indirect Water Heater: Plumbing/Heating101 Questions

seized123

My new indirect hw heater arrived yesterday. After weighing a lot of good advice on another thread about what kind to get, I decided to go thermoplastic with the Burnham Alliance AL55LT (55 gals). Now I have to install the thing. Another learning curve!

Below (in the next comment) is the installation diagram from the manufacturer. Pending further input (please comment on anything that follows here), my current plan is to follow the diagram as closely as possible. One immediate difference however is that unlike in their picture my expansion tank (for the closed boiler loop) is located on what the diagram labels the "Boiler Return" just before the circulator and just after the pressure reducing feed valve - but my understanding is that's okay, so I plan to leave it there unless I hear otherwise.

Note that they recommend another expansion tank on the "Cold In" line to the tank (domestic water from the well). On the phone Amtrol recommended their Therm-X-Trol ST-5 for this, which I think comes precharged to 50 psi, and since the switch at the well pressure tank keeps pressure at 30-50 psi I guess I would leave it that way?

In the manual text the manufacturer also recommends another T&P valve on the cold water input for systems with a well or with hard water, and I have both. I figure it should be with the same settings as the one on the DHW outlet, which was included with the heater?

Also, I know there's something called a heat trap, do I need to build those into the lines? If so, where?

And I know there's something called a mixing valve. If that's the thing that makes sure the hot and cold water are balanced so you don't get scalding water, I think there's one at the upstairs bath/shower but not on the downstairs. Is that something I should be putting on at the water heater? If so, where, and recommendations?

seized123

Jamie Hall

You have, I assume, an expansion tank already on the heating system? If so, you don't need the extra one on the feed line to the indirect. One is plenty.

And, since your system is a well, there is also a pressure tank for the well? If so, you don't another one for the hot water heater. Again, one is plenty.

If you do need one for the domestic side, it must be pressurised when it is empty of water and disconnected -- open to the air or the water side -- to the cutin (low pressure setting) of the well control -- in this case, 30 psi -- not the cutout pressure.

HVACNUT

That diagram is shown using zone valves. Is that what you have?

EBEBRATT-Ed

Your expansion tank location on the boiler return line on the suction side of your circulator is fine

The expansion tank for the indirect as shown in the diagram is "optional" If you have a well tank which you must have the DHW expansion tank is probably not needed if there are no check valves between the indirect and the well tank. The well tank has a pressurized bladder to absorb expansion.

The mixing valve also is an option. Some locations require it if the indirect is heated above 120 degrees. You can heat the indirect to 140 and use a mixing valve to keep the hot water at 120 and it will increase your hot water capacity if you want.

You only need 1 T&P valve on the indirect

seized123

Very helpful points.

HVACNUT said:

That diagram is shown using zone valves. Is that what you have?

Yup, that's what I have.

Jamie Hall said:

You have, I assume, an expansion tank already on the heating system? If so, you don't need the extra one on the feed line to the indirect. One is plenty.

I do have an expansion tank on the heating system, but it's on the closed loop through which the boiler water circulates through the zones, including the zone for the hot water heater, all of which is isolated from the domestic water (pictured at the top of the diagram, though mine is on the return side). The second expansion tank they recommend (besides the one I just described) is for the separate domestic water system, since that water can also expand, so the way I see it the first one doesn't preclude the second. Nevertheless, there is still the question whether I need the second one for my particular system, and as you mention:

Jamie Hall said:

And, since your system is a well, there is also a pressure tank for the well? If so, you don't another one for the hot water heater. Again, one is plenty.

EBEBRATT-Ed said:

The expansion tank for the indirect as shown in the diagram is "optional" If you have a well tank which you must have the DHW expansion tank is probably not needed if there are no check valves between the indirect and the well tank. The well tank has a pressurized bladder to absorb expansion.

Yes, I have a Pentair well pressure tank, and what you guys said made total sense to me. So I did call Amtrol back, and they said while technically it is optional (so you were right), it is better to have a dedicated expansion tank for the domestic water at the hw heater so that the well tank doesn't take on the task of expanding to accommodate hot water expansion, possibly skewing things, and can just do its job maintaining the 30-50 psi normal pressure. He even added that it would be a good idea to put in a check valve just before the second Extrol tank to really isolate the hot water side from the cold water side; thought it's optional that sounds like a good idea to me, so I'll probably do it. But also, something I didn't think about when I posted, is that I have a neutralizer (like a water softener but for pH) between the well pressure tank and the rest of the house, and that probably has some kind of backflow prevention at least when it does its daily circulating thing, so as you say with that possible check valve action the second Extrol would be good to have.

Jamie Hall said:

If you do need one for the domestic side, it must be pressurised when it is empty of water and disconnected -- open to the air or the water side -- to the cutin (low pressure setting) of the well control -- in this case, 30 psi -- not the cutout pressure.

This I didn't understand; it seems to me I wouldn't need or want my second Extrol to start expanding until the hot water caused expansion beyond 50 psi. If it was set to 30 then it would be working almost all the time whether or not the hot water was causing higher pressure, since house pressure is always 30 or over. So I asked Amtrol about that too and they said it should be set to the higher pressure - the Therm-X-Trol ST-5 comes pre-pressurized to 50 psi so I can just leave it alone. (Unless you meant the well pressure tank, that one's set to about 28 psi.)

EBEBRATT-Ed said:

Your expansion tank location on the boiler return line on the suction side of your circulator is fine

Phew!

EBEBRATT-Ed said:

The mixing valve also is an option. Some locations require it if the indirect is heated above 120 degrees. You can heat the indirect to 140 and use a mixing valve to keep the hot water at 120 and it will increase your hot water capacity if you want.

You only need 1 T&P valve on the indirect

Yeah, I could always splice in a mixing valve later if I decide it's needed. T&P valve, yeah, I don't know why they want it for hard water, can always add that later if needed.
All these observations have been very helpful, now I have a better idea what's going on with all these expansion tank possibilities.

Jamie Hall

At the risk of pointing out the obvious, if your hot water pressure tank is precharged at 50 psi, and there is no check valve between it and well tank, it will never do much, if anything. The only time it would begin to do anything is if the water started to heat when the system was already at its maximum pressure, and then it -- and the well tank -- would absorb the expansion. Otherwise it will just sit there.

now. If there is a check valve somewhere between the hot water heater and the well tank, then, yes you will need the extra tank. Between its action and the action of the check valve, the hot water pressure will eventually get to around 50 psi -- its set pressure -- and hold there or slightly over -- until you open a hot water tap, when the pressure will abruptly drop to whatever the well tank is holding before water will flow through the check valve, and won't come back up to the 50 psi for quite a while,,, It will be interesting behaviour...

Perhaps the confusion is in how an expansion tank operates? Below its precharge pressure, there is no water in it at all. The bladder is plastered to the tank wall. If the pipe it's attached to goes over the precharge, water will flow in, compressing the air until the air pressure reaches the water pressure. There is no upper limit to it (unlike you pump pressure switch) except the strength of the tank itself, which is probably rated (for drinking water) at well over 100 psi.

seized123

Should I put in “heat loops” or “heat traps” or “thermal loops” in the domestic hot and cold piping? If so, what should they look like? I picture these things as piping going up from the tank, across some, and then down, like a facing-down rectangular  “C”, then going up into the house. If so, what dimensions? (The tank manufacturer’s diagram, above, shows no loops.)

Sorry about the late reply, @Jamie Hall. I see your point. I do have the neutralizer, so I’ll go with the theory that it can act as a check valve. And the manufacturer was pretty firm about setting the Therm-X-Trol at the cutoff, so I’ll probably do that.

seized123

… So I saw a few things on the internet leading 
me to think heat trap nipples at the domestic inlet and outlet on residential hw tank's may be standard, so these loops may not be necessary. Anybody know anything about that? (Nothing in manual.)

Larry Weingarten

Hi, I prefer the loops of pipe as they create less flow restriction when done right, and they are 100% rather than somewhat leaky, as built in heat traps often are. If you're dealing with a one story building, a six inch deep trap is good on both hot and cold lines above the tank.

Yours, Larry

seized123

Got it, thanks @Larry Weingarten. It’s a two-story but with tank in the basement really three. I figure I’ll try for as much height as I can get in a tight space, maybe 12”-18” or even more …?

seized123

… Now I’m reading minimum 27” rise! It’s the internet, but I’ve seen it several times now.

Larry Weingarten

Hi, I'm a bit of a skeptic of internet facts. Is there a reputable source quoted for the information? It would be a little work, but not too hard to make some traps and see what really works. It would be nice to "see" the results in IR. I'm remembering results of a study from long ago that did use IR and a shallow trap depth. I don't think they tested for different building heights though.

Yours, Larry

seized123

I’ll look,  but I actually found very little information (googling hot water heater heat loops) that wasn’t about recirculating loops.

I might end up taking the “it-can’t-hurt-and-I-have-this-extra-pipe” approach.

hot_rod

Of course a government agency tested various heat trap methods.

Look like a standard Sioux Chief type 270 trap, for one test, trapper nipples for the other. No actual dimensions for the pre-made traps

Siggy has an article discussing heat traps on primary secondary take-offs

As Larry mentioned, vertical distance and temperature gradients are what drive the tendency to induce that hot water movement.

Some light reading for you🤓

https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nbsir84-2851.pdf