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DHW help please - pics attached

OK, sorry in advance for the long post... The back story is that I am currently running a Weil McLain 68 Series (circa 1991) oil boiler with the tankless coil for hot water. When we bought the house in '03, it provided "enough" hot water in the Winter, but not enough to fill the tub when we had little kids. Flash forward, the shower water gets scalding hot for about 2 minutes with the shower handle about half-way on, then you keep turning it up as a shower progresses until you have it on full hot and the water is barely in the category of warm. I wanted to just drop a new coil and a thermostatic mixing valve (vs. the mechanical one there now) in there but the wife insists that we have never had enough hot water ever. So, she called our boiler maintenance company and they came out and said they couldn't/wouldn't touch the system unless we brought it fully up to current code, which is basically impossible, but that's a whole different issue...

OK, so, the wife insists that "we" are replacing the current tankless coil with an indirect DHW tank. I look around and settle on the Bosch Buderus SST250, which I now have sitting in my garage. Also, "we" are replacing it, which means "I" am replacing it. I am an avid DIYer and the only two jobs I don't do myself are cleaning my boiler and cleaning my chimney, so I have the skills necessary, but none of the knowledge.

The current set up is this



Literally every valve and component on this system has a degree of leakage, so I will be replacing a lot of stuff here. My current plan was to tee off where the single circulator pump is for my return line but there may be an easier option. For the hot feed from the boiler, I was going to replace an elbow with a tee up where the current zone valves split off for my 2-zones of heat. Piping in cold DHW and out hot DHW should be no problem. However, I find myself hesitating at the details of what I don't know...

So, the cover plate of the current coil is pretty rusted, so I was planning on removing that plus all the plumbing associated with it. I got a blank cover plate and gasket, which I assume is the correct thing. I was thinking of using the Taco 007e-F2 EMC on the tank return line back to the boiler. My original thinking was that I could just split off a third zone valve and return into the current 2-way tee return using the existing circulator pump, but the one thing my boiler maintenance company said, aside from, "No," was, "I suppose you could do that but we don't do it that way." In all the installation instructions, I see various references to needing check valves. I would think those would be on the boiler to tank side. However, when I looked carefully at the installation diagrams, it seems like they all have the circulator pumping INTO the tank and the check valve on the tank to boiler return side. So, I'm kinda lost. I know I need to buy a circulator, a few ball valves, copper pipes and probably some different iron pipes and tees to shorten up the circulator return on the heating side to tee off below that pump. I will also need a thermostatic mixing valve to replace the current (probably stuck and definitely leaky) mechanical mixing valve. I need a new pressure relief because the one I currently have isn't blowing when the water is at 40 psi. In case you're wondering, I think the water is at 40 psi because the hot water coil, I theorize, has a big hole in it, so I get full municipal supply pressure. Lastly, I assume, since I had over-high pressure, I probably need a new expansion tank and I definitely need a new air bleeder valve and pressure gauge (reads about 5 pounds too low, according to the furnace guy who last serviced my unit).

So, can anyone give me some guidance or advice? Is my plan sound? Are there any glaring elements which are way harder than I think the need to be? Is there some aspect which I am totally missing? Is there a totally different, much easier and/or cheaper route which I can take which will provide superior performance? Please, comments, criticisms, I can even take people calling me a dummy for my totally inexperienced (as far as heating systems go) perspective. I'm also looking for advice on what thermostatic mixing valve to use. I read some good things about the Honeywell one, but then I also read some bad things. Some installs, I see an expansion tank on the hot water heater. Do I even need this or will the one on the furnace suffice? Or is that on the potable side? If it's on the potable side, is that because there should be a backflow preventer valve on the supply and the hot water needs someplace to expand to?

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,355
    edited November 2020
    You might want to redesign the near boiler piping with the circulator on the supply side, pumping away from the expansion tank. I will work up a diagram shortly.
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
    RiBillHVACNUT
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,355
    edited November 2020
    Here is a slide from a class I taught on Hydronics. I added your water heater to the diagram.

    Since you mentioned that you are going to do a major refit because of various leaks etc. You may as well start from the beginning and do it right.

    The theory is explained in @DanHolohan's book, "Pumping Away", the practical application on your system would be to put both circulators on the supply pipe, after the expansion tank. also have the boiler fill valve connected to the same place as the expansion tank as indicated in the drawing.

    The zone valves on the space heating system will prevent the Domestic Hot Water (DHW) Circ from pumping heat thru the system backward if the zones are closed. You will need a flow-check on the DHW piping to prevent the space hearing circ from causing overheating in the DWH tank

    The control setup can be easy with a Taco SR501 or Honeywell R845 relay. set up the relay to power the circulator with contacts 3 and 4 (4NO on the Taco) and use 5 and 6 to power up ZR on the boiler control. I can draw the diagram if needed
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
    RiBill
  • ethicalpaul
    ethicalpaul Member Posts: 3,121
    Why do you want to have to keep your boiler hot all summer, heating up your basement and burning so much oil?

    Try this: https://www.homedepot.com/p/Rheem-Performance-Platinum-50-Gal-10-Year-Hybrid-High-Efficiency-Smart-Tank-Electric-Water-Heater-XE50T10H45U0/312742081
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
    RiBill
  • RiBill
    RiBill Member Posts: 8

    Here is a slide from a class I taught on Hydronics. I added your water heater to the diagram.

    I assume the blue oval represents the expansion tank and the blue rectangle is the water heater. What is the small yellow rounded rectangle?

    Currently, in my system, there is a feed coming out the top of the boiler which "elbow-tees" (looks like an elbow with a threaded hole on top) off with an air bleeder on top and a black iron pipe about 15" long to the expansion tank which is kind of crammed in there facing sort of upward at an angle. One time, it failed, filled with water and managed to drop down, unscrewing itself and water was pumping out slowly. I used a cable to strap the replacement tank to keep that from happening again, but, as I mentioned, I think it may be shot.

    As for the design you posted, I assume a Taco 007e (which has an integral check valve, according to the specs) would be adequate instead of a separate check valve and circulator? Is there any reason to replace the existing circulator with a second 007e or should I just reuse it?
  • RiBill
    RiBill Member Posts: 8

    Why do you want to have to keep your boiler hot all summer, heating up your basement and burning so much oil?

    Try this: https://www.homedepot.com/p/Rheem-Performance-Platinum-50-Gal-10-Year-Hybrid-High-Efficiency-Smart-Tank-Electric-Water-Heater-XE50T10H45U0/312742081

    I considered that, but for the "whole different issue" I mentioned in my initial post. Electric is SUPER expensive and climbing higher ever few months in Southern New England. Also, my experience with electric hot water heaters is that that only last 10 years, tops and sometimes as little as 5 years. Lastly, the "other" issue is that our boiler vents out the side of the house, directly underneath our deck. Worse, it's the South side of the house, so in the Summer, the exhaust fumes back draft into South-facing open windows. We could install a chimney, except the furnace is directly under the kitchen with no suitable walls to run it through. So, it would have to be external, up through our deck and soffit. It would require roof modification and carpentry plus it would tower far above the back side of the house to meet code. Oh, and the chimney work alone was quoted as $10k. The only other options are switching to electric heat or switching to propane. The propane company will give us a tank and let us bury it, but the only location we could put it would be in our front yard, which would require taking out some mature trees. So, the indirect water heater seemed like the most portable option and the unit we selected has a 10-year full warranty scaling down to a 25% warranty from 15 onward.
  • HVACNUT
    HVACNUT Member Posts: 4,187
    You would need to repipe the return regardless so pumping away is the way to go. The steel pipe between the boiler and circulator is just bolted to the block using a circulator gasket. 
    RiBill
  • RiBill
    RiBill Member Posts: 8
    HVACNUT said:

    You would need to repipe the return regardless so pumping away is the way to go. The steel pipe between the boiler and circulator is just bolted to the block using a circulator gasket. 

    Yeah, I'm experienced with that. One time, my heat went out. The boiler people came and said my circulator was not working at all and they replaced it. For some reason, they opted to NOT put in gaskets. About two weeks later, we had a power failure and the boiler cooled off to room temp. The iron-to-iron joints started leaking like crazy. Fortunately, the gaskets are something my mini-sized box store actually carries in-stock.
  • ethicalpaul
    ethicalpaul Member Posts: 3,121
    edited November 2020
    That's a heat pump unit, it's going to cost less to operate than a gas unit, and WAY less than firing up your massive boiler just to pull some hot water out of it. But you do you :)
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
    RiBill
  • RiBill
    RiBill Member Posts: 8
    That's a heat pump unit, it's going to cost less to operate than a gas unit, and WAY less than firing up your massive boiler just to pull some hot water out of it. But you do you :)
    My boiler costs roughly 3-3.5 tanks of oil per year. About half a tank lasts me from Apr/May when I turn the heat off until Dec. 1st when I turn the heat back on. In any case, I have the selected water heater in the garage now, shipped by freight, so it's the chosen way. I strongly teetered back and forth between electric and indirect. I figured I could offset the electric costs with solar, but the total cost of ownership was above the indirect unit.
  • MaxMercy
    MaxMercy Member Posts: 177
    RiBill said:

    Electric is SUPER expensive and climbing higher ever few months in Southern New England.

    Ain't that the truth. If prices get any higher it might be cheaper to build a small power plant for every house...
    RiBill said:

    Lastly, the "other" issue is that our boiler vents out the side of the house, directly underneath our deck. .......We could install a chimney, except the furnace is directly under the kitchen with no suitable walls to run it through. So, it would have to be external, up through our deck and soffit. It would require roof modification and carpentry plus it would tower far above the back side of the house to meet code.

    Yikes. At some point, this house will be sold (unless you've discovered immortality and, speaking for the group, we would be thrilled to know the secret!) and it will have to be brought up to code unless you sell to a flipper.

    I'm not a fan of mod/con boilers personally, but this might be the time to get it all done at once. If you follow the advice here and replumb the boiler to add your indirect, I'd like to submit that it might be a better idea to wait until spring and install a direct vent boiler. You're looking at almost the same amount of work anyway, and adding the cost of the boiler won't be a huge deal in the scope of the project. This will bring the house to code, will be safer, and you'll be all new. You also won't have to modify your home's structure and add a chimney.


    RiBill
  • Zman
    Zman Member Posts: 6,965

    Why do you want to have to keep your boiler hot all summer, heating up your basement and burning so much oil?

    Try this: https://www.homedepot.com/p/Rheem-Performance-Platinum-50-Gal-10-Year-Hybrid-High-Efficiency-Smart-Tank-Electric-Water-Heater-XE50T10H45U0/312742081

    Did you miss the part where his wife said there has never been enough hot water? :)
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    RiBill
  • Zman
    Zman Member Posts: 6,965
    The simple way to do this would be to just add a zone valve. A little Taco zone controller like this https://www.supplyhouse.com/Taco-ZVC403-4-3-Zone-Valve-Control-Module-with-Priority?gclid=Cj0KCQiAnb79BRDgARIsAOVbhRoVBdKBEBC8Hvzwb-5RPGpQSJPdNZl81HCgzRvMeN1TkxxosmaW6gkaAiUkEALw_wcB will give you domestic priority and eliminate the need for balancing between the heat loops and the indirect.
    You would not need any additional pumps or check valves.
    It would be a good idea to move the main circ or expansion tank so you are "pumping away".
    Unless it is leaking, you might just "let that sleeping dog lie" with the tankless coil. If it is not leaking, just leave it there. If you snap off those 40 y/o bolts, you will spend more time fixing that issue than the entire repipe.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    RiBill
  • RiBill
    RiBill Member Posts: 8
    Zman said:
    The simple way to do this would be to just add a zone valve. A little Taco zone controller like this https://www.supplyhouse.com/Taco-ZVC403-4-3-Zone-Valve-Control-Module-with-Priority?gclid=Cj0KCQiAnb79BRDgARIsAOVbhRoVBdKBEBC8Hvzwb-5RPGpQSJPdNZl81HCgzRvMeN1TkxxosmaW6gkaAiUkEALw_wcB will give you domestic priority and eliminate the need for balancing between the heat loops and the indirect. You would not need any additional pumps or check valves. It would be a good idea to move the main circ or expansion tank so you are "pumping away". Unless it is leaking, you might just "let that sleeping dog lie" with the tankless coil. If it is not leaking, just leave it there. If you snap off those 40 y/o bolts, you will spend more time fixing that issue than the entire repipe.
    Unfortunately, it IS leaking, internalĺy and externally. As of now, the external leaking is "sealed" with rust. The studs look clean and new, though. It might be possible to cap the ends and hope the rust stays sealed. I'd feel more comfortable with a gasket and a solid plate on there. 
  • Zman
    Zman Member Posts: 6,965
    Well that would be a problem. presoak the bolts with penetrating oil and apply heat if needed.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    RiBill
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,355
    edited November 2020
    RiBill said:

    Here is a slide from a class I taught on Hydronics. I added your water heater to the diagram.

    I assume the blue oval represents the expansion tank and the blue rectangle is the water heater. What is the small yellow rounded rectangle?

    Currently, in my system, there is a feed coming out the top of the boiler which "elbow-tees" (looks like an elbow with a threaded hole on top) off with an air bleeder on top and a black iron pipe about 15" long to the expansion tank which is kind of crammed in there facing sort of upward at an angle. One time, it failed, filled with water and managed to drop down, unscrewing itself and water was pumping out slowly. I used a cable to strap the replacement tank to keep that from happening again, but, as I mentioned, I think it may be shot.

    As for the design you posted, I assume a Taco 007e (which has an integral check valve, according to the specs) would be adequate instead of a separate check valve and circulator? Is there any reason to replace the existing circulator with a second 007e or should I just reuse it?
    The yellow rectangle represents a micro bubble air vent. When I made this slide the only two manufacturers were Spiro vent and Sparco vent. Both brass construction ... hence Yellow.

    Yes to the check valve question. If the pump has one built-in, you don't need to add another.
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
    RiBill
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,304
    Ahhhhhh, freaken tankless coil gasket leaks! 

    Never seen one.....nope....never.....
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    RiBill
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,355
    Look at this book http://media.blueridgecompany.com/documents/ZoningMadeEasy.pdf
    Starting at the bottom of Page 13 is a discussion on the piping design I mentioned. It is explained in easy to understand terms. Even I understand it
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
    RiBill
  • RiBill
    RiBill Member Posts: 8

    Look at this book http://media.blueridgecompany.com/documents/ZoningMadeEasy.pdf
    Starting at the bottom of Page 13 is a discussion on the piping design I mentioned. It is explained in easy to understand terms. Even I understand it

    My original thinking was to just add a third zone valve as a priority zone switched by aquastat on the indirect heater and add one additional leg for the circulator, replace all the leaky bits and replace the tankless cover plate. I was under the expectation that I might need to get a zone controller, as I don't know what I have for that right now. The original installer sent wires down and up and down and up again and then zip-tied them all together. One furnace tech, one time, said, "I hate when plumbers hook this sh*t up." When I asked what he meant, he said, "There's a right way and a lot of wrong ways. Whoever installed this, did it the wrong way." Of course, he left everything exactly as it was, so I'm not sure how "wrong" it could actually be.
  • RiBill
    RiBill Member Posts: 8
    I should reiterate that, as I said, aside from telling me 'No,' the only thing my boiler people said was that it could be done that way but they don't do it that way. Seems like it would be the least invasive, as the zone controller would ignore the call for heat and give priority to the hot water. It has a potential issue where a circulator going out would kill the heat AND hot water, but I would rather just keep a spare on the shelf and have the mechanically, electrically, and hydronically simple system.