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gas fired water heater vs indirect

ed wallace
ed wallace Member Posts: 1,613
need to show a customer which would be better a 10 yr warrented gas water heater vs an indirect whats the pay back time on the indirect have all ready gone over the warrentee issue


  • $$

    Depending on size I'd bet price wise the indirect would cost about the same (maybe alittle more) as a 10 year. Lots of variables there. My money would go with an indirect, without a doubt.

    Robert O'Connor/NJ
  • Rich Kontny_2
    Rich Kontny_2 Member Posts: 24
    With the

    Indirect,one less gas line,one less stack pipe and one
    less worry about combustion air.My pick is the indirect as

    When money is not a object..Whats that like?
  • jeff_51
    jeff_51 Member Posts: 545
    the normal water heater

    runs about 75% efficient, your boiler is prolly 82% or better. One power plant instead of two. Less to go wrong. Don't know the % of savings but I bet that is in the literature. Go to the Rheem web site or somesuch and see what there comparisons are on there own product. My choice would certainly be the indirect.
  • Michal
    Michal Member Posts: 213
    indirect without a doubt

    depending on models and where you are a indirects initial cost upfront is a bit high lets say 1500 for a amtrol model 47hp installed lets say indirect was 750 with pipe and 750 to install (for arguements sake only). the heat loss is 1/4 degree per hour and recovery is high if not better then a 10 year 40 gallon hwh. Also lifetime warranty on the amtrol unit. Like some one else mentioned there is only one powerplant and honestly the extra fuel to heat water indirectly is very competitive compared to gas or oil fired heaters. You have to look at each manufacturer differently and price it out and compare $/cfh of gas or $/kwh. Many times the boiler will not turn on to make some water indirectly. But check out sites like amtrol, superstor, or buderus.
  • jerry scharf_2
    jerry scharf_2 Member Posts: 414
    Paging Constantin


    We all know our hunches, but the evidence is hard to find. Water heaters are measured in ER, and boilers in AFUE. There is no mapping possible, they have radically different scenarios. The water heater people don't give out standby loss information, which is the other half of the picture. You have an open stack running through the middle of your hot water heater, and that carries away heat when the burner isn't running.

    Constantin, I know you went through the development cycle with a water heater. What numbers for loss did your unit have and what did your group consider to be the standards of the industry.

    Man would I love someone to just buy a water heater, an indirect/boiler and set them up in a series of tests. All you need to do is set up some valves that demand water at some schedule and measure the gas each one consumes. Ideally, you would do this over a number of environment conditions to model the garage install... Once you have that ratio, then you can build a spreadsheet that allowed the various information like hot water demand and climate, and pop out an operating cost. This is a really simple test and I just can't believe that it hasn't been done.

    LEAD PIPE Member Posts: 199

    Boiler is 82% but its heating water that heats water. There must be an additional loss of efficiency in the 2nd heat transfer. I don't think you would save $ by going to an indirect unless you had a 90+ boiler.
  • jerry scharf_2
    jerry scharf_2 Member Posts: 414
    where did the heat go


    Yes there is a HX, but to lose efficiency the heat has to go somewhere other than the hot water. There may be extra electricity for the pump to push some extra water, but given that most of these run at above condensing temps on the return, there is little system efficiency lost. This assumes well insulated pipes...

    The HX will definitely decrease the recovery rate of the indirect, but that is different than efficiency.

    I am looking to see if U can run the indirect priority mode such that I can get the return water back at less than 140. It will reduce the recovery rate but increase the system efficiency. Won't know how it all works until I get the system up and running. It's one of the summer experiments...


  • ScottMP
    ScottMP Member Posts: 5,884
    I may be wrong

    but I think you are giving a standard natural gas hot water heater alot of credit when you say 75%.

    One inch of insulation, a large chimney up the middle attached to a larger chimney creates a huge draft, and a porly designed burner.

    An indirect is more like a thermos bottle. Low degree loss due to high r-value and I agree with the boilers output.

    I go with the indirect as often as possible.

    Lets talk about the larger capacity units. How big is the flue on a 75 gallon natural gas unit ? Whats the draft on that puppy ?


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  • Ranger
    Ranger Member Posts: 210

    ...gets my vote :-)
  • DIYPeter
    DIYPeter Member Posts: 15
    In off-heat-season?

    Wouldn't the effeciency of the boiler be reduced if all it were doing is providing HW through a HX? Doesn't that return the same arguments against oversizing a boiler for heating sytems? I'd like to justify replacing my fairly effecient HW heater with indirect. Peter
    LEAD PIPE Member Posts: 199

    LEAD PIPE Member Posts: 199
    It never gets to the hot water

    Once the water temp on the indirect is satisfied the boiler shuts down. I still have 160 to 190 degree water through out the system, boiler & piping that is no longer needed. The "wasting" of this heat has to be calculated in the cost of heating your hot water? I guess this would be more of a factor during the summer months when the boiler is used exclusively for hot water.
  • ScottMP
    ScottMP Member Posts: 5,884

    How is the 160/190 degree water going through out your systems if all its doing is domestic ? During the summer the piping is going from the boiler over to the indirect, it should never be in the rest of the system.

    Most will agree that having a boiler run occasionally during the summer to make hot water is better for the boiler than shutting it down for five months or so.

    I still belive an indirect is a better investment in the long run than a atmosperic tank.


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  • jalcoplumb_2
    jalcoplumb_2 Member Posts: 172
    If you were....

    to use a Munchking you are looking at a combustion efficency of around 97%. The boiler depending on the size only has a few liters of water in it. Indirect has much more insulation than a standard water heater and loss of about 1/2* per hour.

    If your pipe is insulated you will reduce the loss to a minium.

    An indirect will recover in about 20 to 15 min. in most cases. How long does your standard gas water heater take to recover? 50gal gas 50,000btu?

    10 year warranty vs lifetime? Energy savings? Recovery?

    Hands down Indirect.
  • jalcoplumb_2
    jalcoplumb_2 Member Posts: 172
    most boilers....

    would be 82+
  • J.C.A._3
    J.C.A._3 Member Posts: 2,981
    Anyone else notice....

    The way our computer controls are going lately? Hell with a Tekmar 50.../51..whatever sensor, the control learns and enlists more than the regular homeowner will ever accomplish,in the first few days on the job.I think water heater controls will follow suit soon.

    The darn things will know you and your family better than you know youselves in a couple of weeks and adjust itself accordingly.Couple that with a "smart boiler" control and the limits are endless. My money is on the boiler anticipating that there will be a demand for hot water at an assumed time almost every day, and deal with it,efficiently. (like it or not....we are creatures of habit and will be until our untimely demise!)

    The future IS here. I think we all just need to adapt and let our heating units do the same. Trust me....they will. Chris
    LEAD PIPE Member Posts: 199

    The boiler itself, the water in the boiler at the point of shutdown and any water in the pipes leading to and from the indirect is all hot. Once the tank is satisfied all that heat is wasted, same as if it went up the flue. How many gallons of hot water does the boiler hold?

    Another thought,
    If you wanted to get water to 120 degrees on your stove top what would be the fastest putting the pan of water right on the heat of putting in a double boiler?

    Now I am pointing this stuff out as factors, that doesn’t mean I wouldn't go indirect. In fact I did, last year, and I love mine. I just don’t think you can take the efficiency of the boiler and say that = the efficiency of the indirect.
  • Steve_35
    Steve_35 Member Posts: 546

    In most cases the boiler is smaller than the water heater could really use so the boiler would generally only be oversized relative to the WH if the heat loss of the house were fairly large, like a large older home w/few energy upgrades.
  • John Shea
    John Shea Member Posts: 247
    Outside the box...

    My knowledge of indirect is very limited, but isn't it true that with indirect you have 'unlimited' supply of domestic hot water?

    With four(4) daughters in my house, I highly doubt that this luxury would be efficient on my wallet.

    In fact, I'm thinking of going from a 40 gallon to a 30 gallon!
  • Steve_35
    Steve_35 Member Posts: 546

    No, you generally have fairly fast recovery, but it's far from unlimited. Most of the time around here the boiler output is the limitation.

    It takes about 46,500 btuh input to give 1gpm of hot water continuously with an 80º temp rise. So a boiler with 100k input will give you a little over 2gpm non-stop.

    OTOH, a gas fired WH generally won't give 1gpm continuously.
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,294
    OK Jerry.

    This may be what you want. A very nice man, Jim Lutz developed an algorithm called WHAM. It is an accurate way of predicting water heater performance.

    Enjoy! Yours, Larry
  • Constantin
    Constantin Member Posts: 3,782
    Someone calling my name?

    Hi Jerry!

    I've been traveling in places where internet access is as rare as, well, I dunno. Now I'm in transit, reconnected to the wall... more travels to go before we get home.

    Way back when, the primary design objective for the outdoor water heater was designing a water heater that could withstand any wind conditions we could throw at it while passing emissions requirements. Secondly, it had to be as cheap as possible, so we used a lot of extant parts. Combustion efficiency was a nice to have, but we did use 2" of exterior insulation.

    Combustion efficiency in a conventional gas water heater is basically a function of the length of the baffle that is inserted into the flue... the more baffle plates, the better the HX, but sooner than later you get CO and other nasties.... Given my NDA agreement with ADL, I'm not at liberty to discuss the actual specifics of the unit w/o permission from AWH even though ADL went under and AWH has withdrawn the unit from the market (bad sales, not a bad design...)
  • Scott Denny
    Scott Denny Member Posts: 124

    Recently, I received a call from a lady whose Munchkin w/SuperStor indirect was down. Turns out (I didn't make a service call) she had the problem diagnosed and the defective part identified. Unfortunately, the local stocking distributor didn't have the part and it was over a week out from factory. You can huddle around a fire for a week, maybe. But after a few days unshowered, folks get a little gamey. At least with a seperate DWH, in most cases, a replacement is available immediately. With that said, being the optomist that I am, I'd still go with indirect.
  • Steve_35
    Steve_35 Member Posts: 546

    I fidn it hard to believe the part can't be overnighted in or failing that the system can't be temporarily configured to give them DHW.

    What part is bad?
  • Scott Denny
    Scott Denny Member Posts: 124

    What part is bad?

    I don't remember. It was a while ago and I only heard second hand. Instead of her installer, maybe she should have called you. In her desperation she called me and I told her I don't do service. Perhaps HTP was temporarily out of the part as well.

    I find it hard to believe the part can't be overnighted in.

    Whenever people I deal with in other lines of work tell me something will take more than a couple of days to get I ask if they have ever heard of UPS Red Label. I get ticked when, after authorizing Red Label, an item still takes 4 days and I get charged next day air anyway. Or when waiting 2 weeks after an item is promised, I complain, only to be told it's shipping today. Grrrr!
    I do recall one customer who flew a guy 400 miles to a factory to pick up a part as it came off the assembly line and brought it back and to a job site the evening for me to install since I told them that if they could get it, I'd install it whenever it came in. That's one way to beat the system.
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