I added a hot water recirculating pump to an existing dedicated hot water return line. Does the setup look acceptable?

[Plumbum1234]

You are getting close but tying into your cold-water line there is still wrong. You need to tie the warm water return to the cold-water inlet of the water heater below the valve on the water heater. You should also install a check valve in the cold-water inlet to the water heater above that tie-in point so you don't pump warm water backwards into the cold-water line.

I didn't look up the pump, but SHEPLMBR said these pumps are for well tanks. And as most hot water circulating pumps are line mounted and do not need to be mounted on a joist with a vibration pad, I'm thinking this isn't the correct pump.

Below is closer to what I think you're saying (I hope).

There is a check valve built into the pump (I know this doesn't address you question - just an fyi).

Since the pump is such low flow and it should be creating a slight negative pressure on the water heater, wouldn't it be hard for it to overcome the force of the cold-water supply and therefore a check valve isn't absolutely necessary?

She was referring to the tee I was originally suggesting for the tank drain (not going down this route). This is an AquaMotion, Model AMH3K-7 pump which was originally designed to go under a sink, but I am repurposing it since I already have it and a dedicated return line. I also asked the OEM if this is acceptable, and they said yes.

 

[MicEd69]

Water flows in pipes based on pressure differential and not based on pipe sizes. Flush a toilet while you take a shower, and the water temperature changes because the pressure in the cold-water line is reduced at the shower head by the friction drop of the increased flow of water to the toilet. Without a check valve in the cold-water line between the block valve and the tee where the circulating pump enters that line, you will get some warm water going to the hose bibb. And because that will create a closed confined volume system, you will need an expansion tank.

 

[MicEd69]

Below is closer to what I think you're saying (I hope).

There is a check valve built into the pump (I know this doesn't address you question - just an fyi).

Since the pump is such low flow and it should be creating a slight negative pressure on the water heater, wouldn't it be hard for it to overcome the force of the cold-water supply and therefore a check valve isn't absolutely necessary?

She was referring to the tee I was originally suggesting for the tank drain (not going down this route). This is an AquaMotion, Model AMH3K-7 pump which was originally designed to go under a sink, but I am repurposing it since I already have it and a dedicated return line. I also asked the OEM if this is acceptable, and they said yes.
View attachment 33863View attachment 33864

Actually, the pump will be producing a positive pressure at the cold-water inlet to the water heater. The pump's suction is from the dedicated return line and flowing back into the water heater. So, the pressure at the cold-water inlet to the water heater is higher than the cold-water line pressure. And yes, it is a low flow, and yes most of the water to hose bibb will be coming from the main line, but some will come from the warm water circulation pump without that line check valve. The check valve in the pump is to keep cold water backflowing through the pump. Without that pump check valve, you would get cold water flowing backwards through your dedicated circulating line to your hot water faucets if the pump was off. And as Twowaxhack said, you need an expansion tank.

 

[Plumbum1234]

Actually, the pump will be producing a positive pressure at the cold-water inlet to the water heater. The pump's suction is from the dedicated return line and flowing back into the water heater. So, the pressure at the cold-water inlet to the water heater is higher than the cold-water line pressure. And yes, it is a low flow, and yes most of the water to hose bibb will be coming from the main line, but some will come from the warm water circulation pump without that line check valve. The check valve in the pump is to keep cold water backflowing through the pump. Without that pump check valve, you would get cold water flowing backwards through your dedicated circulating line to your hot water faucets if the pump was off. And as Twowaxhack said, you need an expansion tank.

I follow now, I wasn't really considering the hose bibb. I was more so looking at the cold water supply line.

Could I install a check valve and just drill a small hole in it in lieu of an expansion tank? Or is this far from best practice?

And if I were to forgo the check valve, am I still compliant? Would an inspector/plumber like you all say anything?

And if I understand this all correctly, if I'm not using any cold water, then the hose bibb will be mostly (of not all) supplied by the cold water supply. If I'm using some cold water in the house, then the hose bibb will have some hot water from the return line, but most will be from the cold water supply. At the end of the day, is this a big deal? Just wastes mkney on heating water?

 

[MicEd69]

The very first question you asked in your post was, "Does this setup look acceptable or a very obvious DIY job?"

It already has the look of a DIY job by repurposing a pump meant to sit on the floor. But let's overlook that since you have the pump already.

If you do any kind of installation other than a check valve and an expansion tank, it will further the look of a DIY job. The fluid dynamics of a house plumbing system can be hard to absolutely determine without a computer simulation which is hardly ever done for a regular single-family home. But the use of upstream fixtures like toilets, bathtubs, showers, washing machines, etc., can result in some strange issues caused by incorrectly installed hot water circulating systems. Drilling a small hole in the flapper of a check valve would result in relieving any thermal induced pressure increase in the hot water loop provided there is no check valve or other device upstream that prevents the cold-water pressure from floating on the city water line pressure. However, that hole WILL seal itself with calcium deposits or some type of crud over time and is absolutely against every code in the books. Note that without an expansion tank, anyone with just a basic understanding of plumbing will see that as a glaring error. It would definitely not pass any plumbing inspection, nor any general house inspection if/when this house is ever sold.

Sorry, but that's how I see it.

 

[Plumbum1234]

The very first question you asked in your post was, "Does this setup look acceptable or a very obvious DIY job?"

It already has the look of a DIY job by repurposing a pump meant to sit on the floor. But let's overlook that since you have the pump already.

If you do any kind of installation other than a check valve and an expansion tank, it will further the look of a DIY job. The fluid dynamics of a house plumbing system can be hard to absolutely determine without a computer simulation which is hardly ever done for a regular single-family home. But the use of upstream fixtures like toilets, bathtubs, showers, washing machines, etc., can result in some strange issues caused by incorrectly installed hot water circulating systems. Drilling a small hole in the flapper of a check valve would result in relieving any thermal induced pressure increase in the hot water loop provided there is no check valve or other device upstream that prevents the cold-water pressure from floating on the city water line pressure. However, that hole WILL seal itself with calcium deposits or some type of crud over time and is absolutely against every code in the books. Note that without an expansion tank, anyone with just a basic understanding of plumbing will see that as a glaring error. It would definitely not pass any plumbing inspection, nor any general house inspection if/when this house is ever sold.

Sorry, but that's how I see it.

No need to apologize, I'm looking for honest, sound advice. And by no means am I trying to argue with you, just learn. I understand and appreciate that you're taking time out of your day to respond to me.

I didn't realize repurposing the pump looks DIY. Bummer. At least it's not against code, correct?

Good call about the hole getting plugged overtime, I definitely can't argue with that.

So as one last double check, here's my (hopefully) final drawing:

 

[Twowaxhack]

Don’t put expansion tank on the return line. Install it between the water heater and check valve on the cold water side.

 

[MicEd69]

Don’t put expansion tank on the return line. Install it between the water heater and check valve on the cold water side.

Except for a couple of fittings, that is where it is located.

 

[MicEd69]

No need to apologize, I'm looking for honest, sound advice. And by no means am I trying to argue with you, just learn. I understand and appreciate that you're taking time out of your day to respond to me.

I didn't realize repurposing the pump looks DIY. Bummer. At least it's not against code, correct?

Good call about the hole getting plugged overtime, I definitely can't argue with that.

So as one last double check, here's my (hopefully) final drawing:
View attachment 33872

Yes, I think this will be just fine. And the pump you have looks quite new, so I wouldn't worry too much about it looking like a DIY project. Retrofitting these systems, even with a line mounted pump, always require a bit of imagination and compromises even for professionals. Just be sure to support the expansion tank. It can go in any direction, so put it where it fits best. Good luck.

 

[Twowaxhack]

Except for a couple of fittings, that is where it is located.

it should be installed so that hot water doesn’t fill the tank if possible.

I only install them in the cold supply line per the manufacturer

Preferably away from the heater if I can. that’s my preference.

There are also other methods for thermal expansion control other than tanks.

 

[MicEd69]

it should be installed so that hot water doesn’t fill the tank if possible.

I only install them in the cold supply line per the manufacturer

Preferably away from the heater if I can. that’s my preference.

There are also other methods for thermal expansion control other than tanks.

That is best practice. But the Watts brand tanks are rated for 200 degrees F and retrofitting this system into Plumbum1234's existing layout appears difficult without dismantling all the piping and starting from scratch.

So, you earlier mentioned that an expansion tank is required, and now indicate that, "There are also other methods for thermal expansion control other than tanks."

Please provide Plumbum1234 with your other thermal expansion control methods as I'm sure he would be interested in weighing them against your earlier expansion tank recommendation.

 

[Twowaxhack]

Yeah it’s best practice to get a longer life out of the tank. Most tanks can be subject to 200 degrees or more.

There are ballvalves available with thermal expansion relief valves integral.
https://www.homedepot.com/p/Zurn-3-...KErGzRyKcxbW4b2GWVhoCRiAQAvD_BwE&gclsrc=aw.ds
If it was my personal system I would drill an 1/8 hole in the check valve.

 

[Twowaxhack]

You can always cut a tee in between the tank and the check valve then extend piping to a suitable location for the expansion tank. At the water heater is not always possible.

 

[MicEd69]

No need to apologize, I'm looking for honest, sound advice. And by no means am I trying to argue with you, just learn. I understand and appreciate that you're taking time out of your day to respond to me.

I didn't realize repurposing the pump looks DIY. Bummer. At least it's not against code, correct?

Good call about the hole getting plugged overtime, I definitely can't argue with that.

So as one last double check, here's my (hopefully) final drawing:
View attachment 33872

So, there you go Plumbom1234.

Twowaxhack first said an expansion tank would be required, but then a thermal relief valve (which can be integral with a valve or purchased separately) would work, and finally that if this was his house, he would drill a hole in the check valve. But as he is a professional plumber, I really doubt that his last statement is correct.

Many municipalities now REQUIRE expansion tanks for new installations of potentially closed water heating systems, and I don't see anywhere that a relief valve can be substituted for the expansion tank. I'm not sure of the Cleveland area requirements, but an expansion tank is definitely best practice. And I would not be concerned at all about running a tank with a design temperature rating of 200-degrees F at between 125- and 140-degrees F all day long.

Totally your choice, but in my book, the most professional looking installation would be the expansion tank. And as this is a retrofit installation and where you have to install the pump, the least amount of plumbing redo, the better the installation will look.

Again, it's your choice and good luck with whatever direction you choose.

 

[Twowaxhack]

Most places require thermal expansion Control, not thermal expansion tanks. Most any local code department or state code authority can amend the codes though.


I’m not aware of the model codes specifically requiring a tank. It’s just usually the default method. It doesn’t waste any water and doesn’t require a suitable location to dispose of the water.

All methods fail at some point, I find tanks that are as old as the heater and water logged on a regular basis. I find the relief valve type that don’t open.

I would definitely drill the hole in the check valve at my house. I do a lot of things at my house I wouldn’t
do for a customer.

 

[MicEd69]

Most places require thermal expansion Control, not thermal expansion tanks. Most any local code department or state code authority can amend the codes though.


I’m not aware of the model codes specifically requiring a tank. It’s just usually the default method. It doesn’t waste any water and doesn’t require a suitable location to dispose of the water.

All methods fail at some point, I find tanks that are as old as the heater and water logged on a regular basis. I find the relief valve type that don’t open.

I would definitely drill the hole in the check valve at my house. I do a lot of things at my house I wouldn’t
do for a customer.

Yes, in a LOT of places the AHJ insist on tanks, as they have no moving parts, for thermal expansion control.

Using a relief valve for thermal expansion begs the question, "Won't the PT valve on the water heater itself suffice for the concern of thermal expansion?" Yes, it will burp when required just like a second pressure relief valve will, but that would relieve the pressure that has built up due to the heating of the water. in the closed system.

Personally, if I was a plumber instead of a Professional Engineer, I would not suggest anything on this forum that I wouldn't do for a paying customer without first clearly explaining it is against best practice and against code.

 

[Twowaxhack]

The problem with using the T&P valve on the water heater for thermal expansion control is that it’s set point is 150 psi. Well above the 80 psi max of pressure of the potable system.

This can also cause mineral deposits on the T&P valve outlet, that’s undesirable. It’s not meant for thermal expansion control.

There are adjustable pressure valves available. Some are not listed, some are.

Technically the expansion tank doesn't have any mechanical parts, but it does have one part that moves, The bladder. Schrader valves can also leak.

 

[Twowaxhack]

I’ve worked in 5 states and no authority has ever required any specific type of thermal expansion control in a closed potable system. But sure, any local code can amend the model codes or make their own code. I know in some jurisdictions tanks are required, even for tankless heaters.

I could get hired by a local code authority and make all kinds of stupid rules. . The inspectors only make 24k a year

Where the plumbing Union has a strong presence you’ll find all kinds of rules that make little to no sense.