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Why would i want a mixing valve for my indirect hwh?

recently installed Buderus WS-4 and S32 indirect.

the indirect's heat demand is being driven by it's Honeywell aquastat which I had them set to 140 degrees.

why would i additionally need a mixer off the boiler to feed the indirect? does that save fuel usage? does the lower temp used with the mixer reduce the recovery?



  • SWEI
    SWEI Member Posts: 7,356
    The mixing valve

    should be installed on the DHW output of the indirect, to make sure the outgoing water does not scald.
    Jean-David Beyer
  • BarryNY
    BarryNY Member Posts: 13
    Ok - understood

  • matt_sunwaysolar
    matt_sunwaysolar Member Posts: 61
    In addition:

    Heating the tank to 140F will also kill any/all legionella bacteria.

    Additionally, a thermostatic mixing valve will effectively increase the volume of available hot water.
  • Aaron_in_Maine
    Aaron_in_Maine Member Posts: 315
    Anti scald

    State of Maine just made it code for a anti scald mixing valve to be installed on all indirect water heaters.
    Aaron Hamilton Heating
    [email protected]
  • icesailor
    icesailor Member Posts: 7,265

    Because ( EPA) water heaters aren't supposed to be set to deliver water greater than 125 degrees to a faucet. If you set an indirect to run at 140 degrees, you can get overshoot to 150 degrees under certain conditions. That will definitely ruin your day and skin.

    Installing thermostatic mixers on the hot water outlets will give you more 125 degree water at the faucet by mixing more cold with less hot.

    If you have a jetted tub (Whirlpool), and you turn on the hot and cold water and mix the water at the faucet and fill the tub to the correct temperature, you will have hot water to spare in the tank when filled. If you turn on just the hot and cool it to what you want when it is filled, you will run out of hot water on a "normal" tank.

    That's why the mixers are called "Hot Water Extender Valves".
  • Steve_210
    Steve_210 Member Posts: 591
    What make and model

    Do you guys use

    I have had my fair share of problems with mixing valves.
  • heatpro02920
    heatpro02920 Member Posts: 991
    I am still looking

    for the perfect mixing valve, as soon as I commit to one they bite me in the @ss.. I am back to watts 70a {I know, don't say it}, they are my old trusty and seem to work for the longest amount of time.. They come in 1/2 and 3/4, I mostly use them for oil tankless apps... I just ordered a few of the webstone mixers, says dhw and heat, and I spoke to the rep he said they are nice {of course, lol} time will tell, I will try one in my office and let a few customer beta test them. The price looks very attractive...

    In the higher end, taco, caleffi, honeywell {I had a few fail fast}, and Zurn all make products worth looking at.... I have stopped using the honeywell, I haved used the zurns for a few higher temp installs, the caleffi is expensive but seems to be decent, and with the Taco I had one bad out of the box and one that was hard to adjust {could have been the customer, I ended up taking it out, installed it at my sisters house and she never mentioned anything negative..}. But I have installed a bunch of Taco's, but dollar for dollar the watts is simple inexpensive, not as fancy flashy, anti scaldy, but its works...
  • icesailor
    icesailor Member Posts: 7,265

    They are all "Hot Water Extenders.

    They aren't really considered thermostatic mixers.

    I think that Taco and older Califfi valves are related when Taco had a relationship with Califfi. They had a divorce.

    The only problem I ever saw with the higher end mixers were that many were used in the wrong applications and not checked or heat trapped like it shows on the installation instructions. #70A's will burn out if not heat trapped.

    Supply houses usually stock 80* to 180* valves which aren't designed for potable water. Or they use 60* to 120* valves that won't accurately mix at 120* so you get water too cold complaints. If you get a 130* or 140* valve with checks, they work for a long time. I never ever had one fail.

    I never installed as many as you have though.

    They must be heat trapped or checked. You can actually buy the checks and use them in place of the gaskets to stop off use circulation which ruins the valve parts. If you have aggressive water that is reactive to hot water, the quality valves can start sticking in the bore. 70A'a won't do that because their is no bore to stick in. They really are just cheap junk with very little sensitivity. But cheap and reliable when installed properly. Which means, follow the instructions and heat trap it.

  • heatpro02920
    heatpro02920 Member Posts: 991
    edited March 2014
    You hit the nail on the head Ice...

    Follow the instructions and install it properly.. I see SO many tankless installs with no heat trap, no flow restrictors, ect. I installed a OWT4 yesterday, I used a 3.5gpm flow restrictor, a 70a with a 12" trap , unions, a t&p valve 2 drains, and a gauge after the mixer and I am confident there will be no issues for a long time.. But I have gone to many service calls where no flow restrictor was installed no tp, no heat trap, just a tee in the cold line the hot rite into the mixer and the mixed with a st 90 going to the house, there is too much that can go wrong, the mixer will cook, the unit will empty too fast, ect. Just do it rite, follow the instructions and only go back for the tune ups, then the customer will have you change it in 40 years...
  • icesailor
    icesailor Member Posts: 7,265
    Getting smart:

    You'll never know how smart you become when you read the instructions. You'll never know how smart other people will think you are because you read instructions.

    Especially if they don't read them themselves.
  • heatpro02920
    heatpro02920 Member Posts: 991
    edited March 2014

    is that from a fortune cookie? LOL

    I see so many guys {pros} that just do it how they do it and fix it later if its wrong.... I admit I do things certain ways that I like them done, like I still put my circ on the return, water feed under it into the return, others see it and say Im doing it wrong, but they work and I have no problems...
  • icesailor
    icesailor Member Posts: 7,265
    Breaking old habits:

    "" "I admit I do things certain ways that I like them done, like I still put my circ on the return, water feed under it into the return, others see it and say Im doing it wrong, but they work and I have no problems..."  ""

    I do the same.

    Is it easier to tell (when purging) if the return water gets hot, and the bubbles have come, if the system is purged? Or is easier to just get cold water and decide?

    My systems were designed with the idea that I would never have to open any air vent on any baseboard. That I could stand in front of the boiler and fill and purge the whole system.

    #1 thing I always kept in mind was that the fill valve would be out of the way of the door opening so I could get at the chamber. And offset so the return didn't stop the door from opening.

    Simple things in life. My old life.
  • SWEI
    SWEI Member Posts: 7,356
    On the return

    Membrane expansion tanks and circulators both live longer when their lives are spent exposed to lower temperature water.  Fire-tube heat exchangers have allowed us to return to this "old" way of doing things.
  • heatpro02920
    heatpro02920 Member Posts: 991
    edited March 2014
    I find

    the circs last longer, the piping is easier to locate on the pip coming from the low return vs jumbling it all on the supply side...

    As far as purging goes, I like it rite above the circ, so when I purge a zone I can feel the cold water leave it and when it comes out hot that means I have gotten the water all the way from the boiler... If the zone is already hot, I can still tell when the water is all the way from the boiler...

    I had a tech working for me that strongly disagreed, he believed that the circ should be 4" from the boiler on the supply line and the water feed should be piped into the bottom of the air scoop on the supply side. I used to say "that is fine and a lot of people do it that way, it works, but I don't"....

    When I pipe an oil williamson for example, I already know my parts list for all of the near boiler piping {a multi zv single circ system for example..},a bushing for the boiler, 1 1/4" x 4" nipple comes out of that to a 90 pointed left, a 5 1/2" nipple to another 90 pointed up, a 6" nipple, a 1 1/4 x 1/2" black T pointed back, another 6" nipple to a 1 1/4" NPT webstone circ flange, to the circ, to a 1" swt webstone circ flange with purge to the header splitting to each zv zone, then a couple 1/2 x 3" brass nipples a 1/2 npt ball valve, 911s feed, 1/2 sweat ball valve, and your water feed and supply is done.. Then just a simple hi vent on a bell coupling and 8" nipple next to the supply, and black pipe to the supply {used to need a tee there for the lwco, but now they built into the control}....

    So all of my installs look the same, I actually put all the fittings minus the top circ flange in boxes so when I get a williamson install I just grab a box and its all made, I do the same for Utica sf3's. I dont do it for gas boilers since I use so many different ones and some times the tappings are different sizes for different output boilers of the same series...

    I guess we all do it different, I can not say which way is rite, but I know what works for me...

    And ice, that is one of the things that aggravates me to no end, when I go to a boiler and the return is blocking the chamber access, I would say it is this way on 90% of the old installs I see, the only thing worse is when they pipe something so you can not get to the cleanouts, I see a lot of units like this, if its a top cleanout they put the expansion tank 3" from the top of the boiler so you cant brush and vac it, or a side cleanout there will be a 1/2" pipe screwed to the side panel.. That pisses me off, and then you go to an 8 year old boiler that is sooted up at 10 pm pn a 9 degree night and you need to drain and repipe it before you can clean it... I hate that..
  • icesailor
    icesailor Member Posts: 7,265

    Or electricians that mount 4" square boxes with assorted amounts of EMT and greenfield onto the jacket covers that cover boiler cleanouts.

    And they develop an attitude when you tell them you have to get in there to service the boiler. And YOU get an attitude when they tell you how easy it is to just disconnect everything.

    And you have to re-wire the system because they did it wrong in the first place.

    And after explaining for the 4th time, how the control wiring works, you get down to the toddler level.

    Look, see, that 20 amp breaker you put in the panel? That one wire, goes through every control and switch on the system. At the end of that wire, is the burner. When the Sun is in the 7th House, and ALL the starts are properly aligned, the burner will start. But all that has to happen first. If it doesn't, it won't start.

    I've explained that on the phone and some figured it out, some didn't.

    There was once a woman in my area who gave astrology reports on the radio. Her name was Gerri Gianandrea. She called herself "The Sister Of The Stars". I once told someone to call her to understand about the Stars lining up.

    I wired it myself.

    Then, there's the guy who cut off that special plug from the control/on-off switch to the burner so you don't have to disconnect the wiring when you want to swing out the door for cleaning. His reasoning was that he preferred to not have any splices between the switch/controls and the burner. He just liked it that way.  Cluckers.
  • heatpro02920
    heatpro02920 Member Posts: 991
    Yes you are in Mass,

    You need an electrician to wire your boilers, here we do it ourselves..... I remember the first boiler I did in attleboro, at the time I didnt know any mass master electricians and called a company out of the yellow pages, what a mistake that was, romex running from the fireomatic down the wall and to the boiler control, the LWCO was wired but he didnt know to connect the white wire to the probe so he grounded it to the chassis, instead of putting a piece of 18-2 to extend the thermostat wire to reach the control is was stretched across the boiler so tight you could play stairway to heaven on it... I redid the entire job, literally 100% of it, he reused the old firomatic so I went from the firomatic to finish... The worst part was he charged me $850!!!!!!!!!!!!!!!! I was upset to say the least..
  • icesailor
    icesailor Member Posts: 7,265
    edited March 2014
    Quality Tradesmen:

    Like all trades, there are good ones and there are bad ones.

    I spent my career in a small, isolated location. You knew everyone and what they could do. The only times we ever say that hackaroo stuff was from people who brought their hackaroo work with them for display. They were one time Charlies. Usually brought in by out of State contractors and these were their subs. So that gives you an idea of the standards.

    They sort of stand out like a spaghetti sauce stain on the front of your white dress shirt. If that's acceptable, what else is acceptable?


    The way you describe the wiring of the boiler doesn't meet Mass. code of any other code that I know of. Its probably their own Code. The Code of Hack. But their are varying levels of Hack. Like the codes require that the service switch be "In arm's reach when viewing the flame" so you don't have to get up and run across the room to shut it off when it goes BOOM. The Service Switch, mounted on the ceiling next to the Firomatic is NOT within arms reach. But it is mandatory in the World of Hack to connect the convenient receptacle that they added so you have power to work on the burner or around the boiler. But, when you turn off the service switch, your lights go out. BRILLIANT. 
  • hot_rod
    hot_rod Member Posts: 14,879
    Check with local plumbing codes

    I'll bet many, most? require an ASSE listed valve be installed now a days.

    An ASSE 1017 is installed at the tank, a 1070 is intended for point of use, at a tub, shower, or faucet. A 1016 could be a shower valve with an ASSE approved mixer inside. High end Grohe shower valves and others are listed to ASSE standards.

    Not all the extender type valves are listed to ASSE standards. This could put you in a bind, and/ or expensive soft tissue lawsuit, if someone were to get scalded, it can happen in a few seconds!.

    The hotter you run the HW tank, the more mineral precipitation. In hard water conditions, and excessive HW tank temperatures, you may need to de-lime the valve every six months or so. Depends on how many gallons you flow thru them, also.

    I'd estimate

    90% of thermostatic mixing valve failures are due to the valves scaling up. Keep a spare cartridge, soak the scaled one in vinegar or CLR for a few hours and the valve will work troublefree for a long time. Rarely do the wax pills inside fail.

    To build an accurate valve that regulates quickly, 2.7 seconds or less, and accurately, within a degree or so, which the ASSE standard requires, takes tight tolerances. Tight tolerances requires maintenance to maintain smooth, free operation of the spool.

    Remember also, you need a 20- 27 degree difference between the mixed outlet temperature, and the hot water supply. Fall below that ratio and the accuracy of the valve drops.

    So don't expect the valve to mix accurately to 120F if the tank is set at 130F, it needs the 27F or higher delta T for the valve to mix and respond properly.

    AND the pressure between the H&C needs to be 2-1 ratio or less for the valve to regulate properly. Sometimes when check valves are installed, or mis-installed :) No thermal expansion provision, typically on recir pump piping, you might see much higher pressures on the hot side compared to the cold, until the pressure balances the valve will not mix properly.

    Quite a bit of engineering goes into those simple looking 3 way thermostatic valves to make them accurate and dependable.

    Tankless style DHW heaters and thermostatic valves don't always get along either. The valve and the heater keep "hunting" against one another as the wide delta T comes and goes with the burner on/ off cycles.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • icesailor
    icesailor Member Posts: 7,265
    Good Information:

    I've said that for years. That's my experience.

    It made me an a$$hat.

    Welcome to the Truth In theory and application club. It can be lonely.
  • Weezbo
    Weezbo Member Posts: 6,232
    thats my idea of humor,' too

    it is for want of a better word "Manic ..

    The Fireman's house i just did a small one bath basement finish has a boiler setup built to fail.

    i explained a lot to him about anti scald , return water temps , piping bypasses types of by passes a number of minor technicalities in combustion ....

    he calls my idea of manic

    Gallows Humour .

    i somewhat agree with that assessment , lol...

    *~//: )

    even the way i speak sometimes has a very circumnambualative colour.

    so some of what i say does not leak right out the other ear in a conversation ....: )
  • icesailor
    icesailor Member Posts: 7,265

    I was once told by a friend that I had the ability to say the most outrageous things with an absolute straight face, that for years, he thought I was serious. After years, one day, he realized it.

    I considered that the be a compliment. My friend was the driest person I have ever known. So dry that I used to offer him a bottle of water after him saying something outrageous.

    If you can't find something humorous to think about or say, life isn't worth living.