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combi heat dhw gas

bluemoonbluemoon Member Posts: 36
Hello Wall....It's been a while since I've posted but I was hoping to get some insight on wall hung heat + dhw gas fired boilers. I'm in the Sandy storm ravaged area of long island. Many customers are requesting wall hung units in the event that we get tides that high again. If it happens once it can happen again,right? I've installed several Baxi Luna units but the plate heat exchangers only produce dhw 3.3 gpm. Also concerned about servicing them. Especially the expansion tank & plate heat exchanger. It seems the boiler will have to be taken down off the wall to replace them? I plan on getting trained on them when things calm down & I will have more time but can anyone shed some experienced light on them in the meantime? Maybe recommend a superior brand?


  • ChrisChris Member Posts: 3,056
    How Many GPM

    Of DHW are you needing? Viessmann Vitodens 100 CombiPlus will give you the same as the BAXI.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • SWEISWEI Member Posts: 7,356
    wall hung what?

    Plenty of wall hung condensing boilers out there, a number of which I feel comfortable recommending (Triangle Tube, Lochinvar WHN, Viessmann.)  If the DHW demand is at all significant, an indirect water heater is the best solution.  Keep the pump or diverter valve and associated wiring above the projected flood line and you should be OK.

    Combi boilers without a tank are going to suffer in terms of first hour delivery, and frequently end up significantly oversized for the heating load.  You can add a buffer tank, but a properly sized indirect with a properly sized boiler is best.  If there are giant soaker tubs or mega-showers involved, a second boiler or a tankless WH may be in order.
  • JackJack Member Posts: 941
    This is always the lead

    on combi's. You get a customer interested or they are interested initially and the conversation has to start with DHW production. You have to ask the homeowner how much hot water they need and you need to get ownership from them before proceeding with a combi. That my mean doing flow checks on fixtures. The other issue with a combi is water quality. A crapped up plate will not do you much good down the line. I like to see them installed with the same type service valves installed on tankless water heaters so they can be flushed.
  • SWEISWEI Member Posts: 7,356
    good point on ownership

    So much better to clearly define expectations before meeting them (and then being accused of not doing so.)

    A 199k tankless (or two) can support a soaker tub nicely when space heat loads are minimal.
  • Mark EathertonMark Eatherton Member Posts: 5,584
    Having had lived with numerous tankless instantaneous units...

    I relate my experiences to the consumer based on real life/real time experience.

    So long as you are willing to change your life style to accommodate the new equipment, you CAN have a virtually endless stream (~2 GPM) of domestic hot water. BUT, if two people, or one person and one machine try and go for the hot water at the same time, there will be some "issues"... and wet dissatisfied people.

    Honestly, unless you have a WHOLE bunch of people using the DHW with a limited number of bathrooms in a VERY short time frame, scheduling is not that big of a deal. If you do have a whole lot of people, then consider adding storage to help accommodate peak hourly loading.

    As others have stated, water quality is a must for ANY tankless type of heater. If the water quality is not addressed up front, then cost of operation, maintenance and reliability are all going to be on going issues of concern and will leave a bad taste in everyones mouth.

    These systems are not for everyone. If you have a large fixed volume tub that has to be filled, it is going to take TIME, especially if the tub user wants a real hot tub full of water.

    As long as everyone is aware of the limitations of these devices, and are willing to schedule their lives around its availability, they work as advertised. The first time the end users decide to see what happens if they force the system beyond its ability (more than 1 or 1-1/2 users at a given point in time) your phone will begin to ring. I'd recommend that you put all limitations, expectations, warranty requirements etc. in to writing, and have the end user initial these caveats so they can't bring them back to you and throw them into your face.

    Education up front is the best way to avoid future problems.

    If 1st hour demand exceed the capacity of the tankless, adding a tank isn't a deal breaker, and when the tide rises again, you really don't need to replace the tank. Just dry it out, replace any control components that got wet and start over.

    Hanging the boiler on the wall is no guarantee that the next storm might not dump water to a higher level and submerge it as well.

    As I heard a famous weather professor say on TV last week, these weather "events" and "extremes" are the new normal. Get used to the new norm. Learn how to adapt, or be prepared to get run over again, and again, and again...

    Happy New Years!

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • bluemoonbluemoon Member Posts: 36
    As I knew

    Thanks all for your replies....knew all that but was hoping that across this land of ours someone had built a better mousetrap....happy new year to all
  • HDEHDE Member Posts: 142
    edited December 2012
    Bear in mind

    Many tankless can provide more first hour water than tanks and smaller boilers with indirect tanks.

    A tankless or bigger combi can deliver 5 GPM, that's 300 gallons per hour, what it can't do is give you 50 gallons in 6 minutes.
  • Mark EathertonMark Eatherton Member Posts: 5,584
    At what rise....

    As you might know, this is one of those ares that sticks in my craw.

    Your first hour ratings are probably not based on the same degree F rise as my first hour ratings are. To level the playing field, lets assume a 100 degree F rise. Now, how many first hour gallons will you be able to generate?

    As you well know, there are no "standards" to which the different equipment manufacturers can do a cross comparison to allow the consumer the opportunity to evaluate one system over the other, and the marketing department gets to tell the engineering department what they want to see, and the consumer only looks at the bottom line.

    A BTU is a BTU is a BTU, and it can only do so much to water, in a given period of time. Doesn't matter wether its gas, electric nuclear or solar, it still only does the same thing, raising one pound one degree fahrenheit.

    The need for 50 gallons in 6 minutes, is pretty typical of a person with a bath tub. They want it filled with hot water NOW, not an hour from now.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • HDEHDE Member Posts: 220
    edited December 2012
    Tankless standards

    The standard testing rise is 77 degrees. However the popular temp rise numbers published is usually 35 & 70. There are two manufacturers in their quest use different numbers than the rest to try to look better, which is 20 & 30 degrees. Both ridiculous numbers to try to use except maybe the 30 midsummer in southern Texas.

    70 works well for most being that 70 degrees takes the water from 50 to 120 degrees, suitable for most residences. The average condensing tankless will produce 4.9 to 5.2 gpm @ a 70 degree rise. Hint that's how one unit got the model number 94. But it's at 30 degrees to look just a bit better than the rest that use a 35 as the lower number.

    That being said its somewhere in the 6 gpm range at a comfortable and safe bathing temp.

    As far as tub filling goes here's my thoughts- if a large enough tank can fill a soaking tub in 6 minutes, then a single tankless may take 10-12 minutes, which is 4-6 more minutes of opportunity to view my beautiful wife disrobed. Not only that but if I wish to shower at same time to be in the bathroom longer with the nice view as the shower has clear glass, I will have bountiful hot water available to do so.
  • bob eckbob eck Member Posts: 565
    Combi condensing gas boiler

    Take a look at using a Triangle Tube Prestige Excellence (has built in SS indirect water heater that delivers 180 GPH) or their Challenger Combi boiler and water heater that delivers 3 GPM domestic hot water. With both of these boilers you could use a 50 gallon electric water heater with the elements connected and then when you start out you should have a full 50 gallons on hot water. Elements in the water heater will only come on when needed to keep water in the tank at temp. You can also look at using a Delta 1.5 GPM water saving shower head.
  • Bill_MarBill_Mar Member Posts: 5
    combi heat dhw gas

    You might want to consider System 2000. They're not wall hung but they are mounted several feet off the floor.
  • Bill_MarBill_Mar Member Posts: 5
    edited January 2013
    combi heat dhw gas

  • Bill_MarBill_Mar Member Posts: 5
    edited January 2013
    combi heat dhw gas

  • HenryHenry Member Posts: 726
    100F rise

    Our standards are for 100F rise: 40F to 140F. The need for 140F is to be certain that there cannot be any issues with legionella. I have the average temperatures per week for the Montreal waterworks. By the end of January and all the way to March, the aqueduct system can be down to 34F. So now it is 144F rise. 199,000 BTU will only provide 199 GPH or 3.3 GPM at 100 F rise. One regular shower head during the winter will use 3 gpm of hot water. Wash the dishes at the same time, and you are out of hot water! Don't forget about the prepurge and post purge of some of the units which will give erratic temperatures! We have refused to install any combi units since 2007 as the claimed performance was not realistic to Canadian situations. They might work in Germany, Japan, China and Texas, but they don't work in the Great White North. They are also very time consumming for any maintenance or repair.
  • icesailoricesailor Member Posts: 7,265
    Repeat that:

    Repeat that.

    I've been saying that for years. If you have a big load, you need a reserve.

    If you are driving your car down a hill at 60 MPH, and you start up the other side, you don't give it more gas when you have slowed to 45 MPH, half way up the next hill.

    Storage tanks give you  inertia. Those of us who dealt with boilers with tank-less heaters only knew this full well.
  • HDEHDE Member Posts: 142
    how can that be?

    Given the per capita poulation, more combis are sold in Canada then in the states, so I dont understand your reasoning or statement Henry

    Besides thats 3.3 GPM + showerhead in Canada? You guys that wasteful up there? Besides that I doubt anyone showers under 3.3 GPM of 140 degree water. You forgot the mix factors required.

    All over the county users see lower water temps for a few months, its just a adjustment to lifestyle. Constantly you hear the argument of showering wont allow dishes or wash to be done. Whens the last time you started the washer and dishes while taking a shower first thing in the morning? Just sayin
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