dhw bphx loop plumbing question

varadhammo

Hi all,

Hope everyone had a nice holiday.

Yesterday I drained the hot water tank to replace the bottom drain with a nipple & tee for my HX loop and I couldn't get the drain out (it's one of those cheesy plastic ones, it felt like the drain would snap before it would let go). So I'm thinking of this alternate way of plumbing it (drawing attached). There's an extra tapping at the top of the tank which I'd use for the HX loop return, and rather than the send coming from the drain tapping, it would share the cold port and dip tube with the cold makeup supply. Will this work ok? One thing I thought of is that if the tank is being drawn from and the HX loop running simultaneously, the cold makeup water might short circuit the tank and go straight to the HX but as far as I can see this shouldn't really be an issue, BTUs are BTUs. Otherwise, the HX loop will draw from the bottom of the tank through the dip tube and return to the top of the tank. Are there any issues with this that I'm missing?

Thanks!

varadhammo

Oh, one thing i missed in my sketch is that the thermomix valve on the top of the tank has internal check valves on the H and C side.

icesailor

If the bottom plastic drain is now leaking when it closes (they usually do) you will need to get it out. The hack saw blade trick works well. A plastic one is far easier to get out than a bad brass one. If there is a flow check ball inside the cold water fitting, it is technically illegal unless there is a bypass in the fitting for the excessive thermal expansion to go through. Unless the installation Manual requires a thermal expansion tank which the installer didn't bother to read the Install manual.

If it is electric, and has screw in elements, you can use the bottom element tapping which is 1" NPT. Its easier to use the bottom drain.

kcopp

cut the drain out flush. Then either work an " easy out" into the drain or heat it up w/ a torch and work it out. You can run a 3/4" tap into the hole to assure its in good shape. How old is the tank?

varadhammo

Kcopp,

Thanks for the suggestion. I actually got it to screw out fine today, took an 18 inch wrench but it finally let go... Tank's not old, just a year or so.

Ironman

The "extra fitting" is probably the anode rod. You need to get the plastic drained out.

Are you connecting the HX to an outdoor wood boiler?

varadhammo

Ironman,

It's actually an optional t&p relief valve location. The anode is another tapping.

Yes, connecting HX to garn boiler.

icesailor

varadhammo said:

Hi all,

Hope everyone had a nice holiday.

Yesterday I drained the hot water tank to replace the bottom drain with a nipple & tee for my HX loop and I couldn't get the drain out (it's one of those cheesy plastic ones, it felt like the drain would snap before it would let go). So I'm thinking of this alternate way of plumbing it (drawing attached). There's an extra tapping at the top of the tank which I'd use for the HX loop return, and rather than the send coming from the drain tapping, it would share the cold port and dip tube with the cold makeup supply. Will this work ok? One thing I thought of is that if the tank is being drawn from and the HX loop running simultaneously, the cold makeup water might short circuit the tank and go straight to the HX but as far as I can see this shouldn't really be an issue, BTUs are BTUs. Otherwise, the HX loop will draw from the bottom of the tank through the dip tube and return to the top of the tank. Are there any issues with this that I'm missing?

Thanks!

As drawn, it won't work very well.

Its bass ackwards.

Ironman

As someone who sells and installs ODWBs for a long time, may I give you a little advice?

I would not pipe it the way you're attempting. Your making it too complicated and your method will actually cause the HX to foul up much more quickly from any minerals in your water.

All you need to do is mount the HX on top of the water heater. Do NOT put a circulator on the domestic side. Instead, simply disconnect the cold line from the water heater and connect it directly to the HX. Then, connect the outlet of the HX to the cold water inlet of the water heater. This way, the HX pre-heats the cold water to about 140 - 150* and puts it into the tank. No circ is needed on the domestic side because house water pressure will cause flow through the HX anytime a faucet is open.

The boiler side of the HX requires constant circulation so that the HX is hot at all times.

It's that simple. That's the way it is on mine and I've done countless others like that. I've also seen it done the way your proposing and it caused the HX, the lines and everything to lime up in short time.

You may want to install an isolation/purge valve on the domestic inlet and outlet of the HX so it can be de-scaled when necessary since that is likely to be needed eventually - but your method will cause it to happen about 100 time quicker. No exaggeration.

varadhammo

@Ironman,

Yes, thanks for the advice, I appreciate it. I did consider the method that you describe, and down the road (after I see the scale problems you describe...) I may replumb it that way in the end. I did consider doing it that way, and the reason (for better or worse) that I decided against it was:

I'm drawing from storage (1800 gallons feeding radiant floors and DHW), where the minimum usable water temp from storage for the radiant floors is 120* or so and at that point I'd still like to be able to move some heat to DHW. With the "single shot" cold feed through the HX, if storage is on the cooler side, you've only got that one pass to move BTUs from boiler side to domestic, so the electric ends up shouldering more of the load. My goal was to keep the electric off as much as possible. With a circ and multiple passes I should be able to get more heat and still be ok with a relatively small and inexpensive HX.

This is my reasoning; of course if it scales up as quickly as you indicate, then that would probably cancel out any gain (real or imagined) in efficiency in my approach, so I guess time will tell.

That said, I have indeed used Webstone purge valves on both ports of the domestic side of the HX, and have wye strainers in place on both boiler and domestic sides as well, and a Caleffi dirt separator next to boiler/storage.

icesailor

@Ironman:

You may have done more 3rd world storage tanks that I have, but probably not longer than I have been doing them. I've done them about every way that someone else said to do them that didn't work anywhere near as well as another way.

First off, if a HX coil is going to "lime up", it doesn't matter where you put the HX. It can be 100' away. Its the hot water on the hot side that caused the mineral rich Potable water to change and insulate surfaces. Or, why you are regularly supposed to flush water heater tanks to get the debris out of the bottom to stop that popping and hissing as the water boils inside the pile of crap in the bottom of the tank. If you are going to have limed up HX's or coils, you need filtration like Water Softeners to get rid of the hardness.

Its my experience that you ALWAYS feed the tank in and out with street pressure. And circulate the heat source through the tank. So you always have full street pressure in the hot side of the tank. As soon as you try to start running the cold street pressure through a restricted place like a HX, you drop the entire hot water pressure under higher flows. I've used gas and oil fired hot water heaters as heat sources with added tanks as storage tanks, where the pressure into the potable water system was full and unrestricted.

Where I worked, I worked on a large hotel. Designed by a registered Mechanical Engineer, it had two large Smith 2500 series boilers with tankless coils. 3/4", increasing to 1" CTS, A 400 gallon concrete tank over the boilers. The Potable water fed the tanks on the cold and hot, full sized. The coils were on a separate loop with a bronze circulator. They didn't run out of water. They weren't trying to "blend" cold water through the coils. Every large storage tank I have ever seen had the cold and hot piped direct through the tank. Anyone that had the attempt to "blend" the water in a coil didn't perform as well as one that didn't. A number of years ago, they did a Renovation and removed the old DHW system. But a couple of oil fired water heaters in. They ran out of hot water constantly.

In the case of storage tanks in residential use, most of the time that the circulator pump is running to make hot water, there is no hot water draw.

If you have a high recovery storage tank that "Stacks" like oil fired water heaters, put a recirc. on it. It mixes the water and stops stacking.

And if you don't put a circulator on it, connected to a thermostat, how do you control the tank temperature when the tank has no draw for 24+ hours?

Been there, done ALL of that.

Do you have any idea of how many plate HX'ers I have seen in scrap barrels that the person that took them out said they were JUNK? And all they needed was to have the plates cleaned of calcium insulation build up with some acid.

icesailor

Like this:

From a Top Performer, where the hot boiler water reacts with the mineral rich tank water. How do you clean it without removing the coil?

Ironman

Ice,
My point was that by constantly circulating hot water through the HX, it will foul many times quicker than just making one pass through it.

The ODWB distributor that I do installs for had an installer that insisted on doing it the way that Varadhammo has diagrammed in spite my specifically telling him not to. He was trying to assure that the elements would never come on. Something that was not necessary and would have probably used more energy from the extra circ running 24/7 than the element coming on occasionally after 24 hours due to no draw of hot water. The poor fellow accidentally killed himself being careless with a loaded pistol. Any way, I had to go behind him on a lot of installs and re-do them they way I described above. Some of them had to have lines replaced because the were fouled so badly that no flow was coming through. On one, we had to replace two 3/4" x100' underground lines that were completely plugged for their entire length.

Using a large enough plate HX (usually a 5x12" 20 plate) will cause virtually no appreciable pressure drop on either circuit and with 170* supply water will usually give 140 - 150* output on the domestic side.

@‌varadhammo
I would highly recommend that you use a large enough HX to minimize any delta T between the circuits with one pass rather than constant circulation on the domestic side. A water softener would also help greatly, but I don't like the idea of your body taking in all that salt that doesn't get flushed during regeneration.

icesailor

@Ironman:

If you've never read me, the only reason I use electric tanks is because they are CHEAP!!!!!. The cheapest insulated tank you can buy on the market. The circulator only runs long enough to satisfy the demand. The fact that the cheap electric water heater comes heavily insulated with thermostats already installed is a plus.

Everyone here (including you) can't get it though your understanding that the electric elements are not connected to any energy source and contribute absolutely NOTHING to the cost of heating water. NOTHING!!!!!

You think that I haven't installed Indirects, Mod/Cons, gas boilers with gas water heaters, gas boilers with Indirects, Oil Boilers without Tankless, oil boilers with tankless, instantaneous wall hung DHW. I've done them all. If an ingenious way to provide hot water someplace was needed, I figured out a way to do it.

If you have someone that doesn't want to get a new Mortgage on a new State of the Art heating system, and has a working oil boiler that is working with a tankless, connect the coil to the tank like a 1920's sidearm heater with a circulator, connect the bottom thermostat with 110 volt power, acting as a switch, and let it rip. If you can do it any more effectively and cheaper, knock yourself out.

My last house, I had completely hired out. The Contractor supplied the Plumber/heating company which I approved. They did NOT want to do what I wanted with a water heater storage tank. They connected it up to my Weil-McLain WTGO-3 and it didn't work to my wife's satisfaction. They followed the instructions that J.R Woods gave. I changed it to how I do it. It worked fine. Until it started leaking 8 years later. I replaced it with a A.O. Smith electric water. Which was the exact same water heater as the J.R. Woods heater that would have been a special order and hundreds of dollars more in cost. The only difference? The elements were not installed and they had 1" NPT plugs in place.

Don't try to lecture me on how another way is better and cheaper, I've done and considered them all. You still don't understand where I come from. Simplicity is my game. If it would EVER been more financially been more advantages to do it another way, I would have. Even when my power company was giving electricity way for $015 per KWH, the large amount that my electric bill would have gone up. didn't come close to equaling how much my oil bill might have dropped. It would have cost me more to heat water. And the boiler runs on Standby at 140 degrees until there is a heating call. 365 days a year. The only electrical power comes from am extension cord to run a Taco 006 BT circulator. Less than an amp to run. A few hours a day and all the hot water that a family of 6 could ever use.

Oh yeah, I almost forgot. My wife never ran out of hot water when giving her horse a nice warm bath. If the water went cold during a horse bath, that was grounds for a division. My old house, we had up to 22 horses on the property. All getting hosed off with warm water after being used. Horses aren't stupid. You could let them go and they would walk right into the wash rack for a warm hosing. Just like my Australian Shepherd dog. If the water was cold, he wouldn't stay there. If it was warm, as long as the hose ran, Martin was there. Martin needed it. He slept outside. Never went inside. He slept on top of the manure pile, guarding the property from interlopers and intruders. Sometimes after it snowed, all you saw was the top of his head where the snow melted.

Ironman

@icesailor‌
I have no idea how this last rant of your has any connection with my comments about Plate HX fouling more quickly because constant circulation is being used.

First of all, you have no idea what I think and second, I'm not lecturing you about thing: that would be an exercise in futility.

Much to the contrary, it is you that try lecture. Anyone that reads your posts can see that clearly.

icesailor

I'm not "lecturing" anyone. Especially you. Only posting my experiences.

YOU brought up the issues of liming up and that of you didn't pump the way YOU did, that the coil would lime up. I only said that in my experience with the area I worked in, some places in the 50 sq. mile isolated area, you could get severe liming and others, you didn't, but that it didn't matter how you piped it. If the raw water came in contact with a hot surface, that the Lime (or whatever it is) will precipitate out onto the hot surface. Like on the coils I posted, and in the bottom of direct fired water heaters. If anyone is being lectured, it is me. That what I have done for many, many successful years is wrong and I should know better. I never ripped any out. OBTW, those old 30 gallon storage tanks they used to sell? They were gas water heater tanks without the gas burner and the hole for the gas valve was where you put the other water connection. They worked. I found a better way to make them work. And they DID work better.

You're way smarter and more experienced than I am. Where you are NOT more experienced in is being the single guy, given a problem that everyone else has walked away from, and I'm now on my own. When I would call Tech Support about some complicated issue, that I have already gone over everything, I get the same bored support, Until they realize that I have an understanding of the physics involved and how it is supposed to work. Including enough electrical to understand the concept. Then WE fix it. 90% of what I was presented with was not of my own doing. Someone called me in. I used to "fix" things just to get the opportunity to look at it. Then fix it for the experience and learning.

I have this concept I developed years ago. About "learning" is like a pyramid. Its easy to learn a lot about something at the beginning. The more you learn about something, the harder it is to find the pearls. The higher up you get on the pyramid, the harder it is to find them. You never find the one at the top. Because the pyramid keeps growing. We all have our own personal learning Pyramids. How we use them is up to us.

At 71 years old, I can't keep it. I can't work and use it. So I give it away.

If you don't like what I say, don't read it. One of these days, you won't be reading it anyway. Unless you read archives.

BobC

The pyramid concept is a good one, the higher you build the pyramid the more you know and the more you know the easier it gets to connect the dots.

When I left my last job and wandered off into retirement one of the new guys paid me a nice compliment. He said he was grateful that I never talked down to him and always listened to his opinion about what might be wrong with a broken piece of mail sorting equipment. I told him I always welcomed another mans opinion because they saw the problem different then I did and that difference often pointed the way to a solution.

I never met a man I couldn't learn from, it wasn't always something I wanted to learn but even that has a value.

Bob

icesailor

"" I never met a man I couldn't learn from, it wasn't always something I wanted to learn but even that has a value. ""

Often, the people we learn the most from, have no idea what they taught us. Sometimes, the most complicated situations we deal with have the simplest solutions. You never know who will give you something you need. Over 40 years ago, I was plumbing this house for a guy with 5 daughters. His youngest must have been 10 years old at the time. She was watching me get ready to caulk a 4" closet flange. She said to me matter of fact ally, "That pipe is cracked". I ignored her as a comment from a 10 year old girl. She then said "That fitting is cracked". So I looked. It was. Had I poured the lead, it would have been a SOB to get out.

jonny88

Bob,Ice please continue to share your war stories,there is some of us out here who still respect the "old timers" when plumbing was a real trade.

icesailor

I remember hot that the fitting was an XH 4" Wye & 1/8Bend with a 4" X 3" copper Manoff and an End Cleanout to go out through a foundation wall. It was the hub of the branch of the 4" Wye that was cracked.

Failing memory.