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I will have a biler. Should I install tankless water heater?

Vad
Vad Member Posts: 55
            Hello All,

           I am planning to install a boiler with baseboard heating. I would like to have my house energy efficient. Having this in place, does it make sence to install instant hot water heating device (tankless, on gas) for domestic hot water? Maybe since I will be heating Hot water for radiator anyway for at least half a year (I live in NY) it is more economical to have regular water heating (with the tank)?

Thank you,

Vad

Comments

  • kcopp
    kcopp Member Posts: 4,431
    edited August 2010
    why not do....

    both in 1 unit. There are many Combi- boilers out there. Notably Embassy Axia, Embassy Onex, Baxi has a couple of units.... as well as the Triangle tube Excellence. All are gas units.
  • bob eck
    bob eck Member Posts: 930
    tankless gas water heaters

    If you are using gas and did not install the boiler yet look at triangle tube high efficiency prestige excellence 95% AFUE boiler 110,000 btu input with 14 gallon stainless steel indirect water heater built in. If 110,000 btu boiler will handle your house heat loss and you have 2 normal bathrooms (showers) with one shower head use alsons 1.6 gpm shower heads and the indirect will produce 180 gph of domestic hot water. can run both showers at one time. if you need higher btu look at their prestige solo and their smart stainless steel indirect water heater 30 gallon up to 120 gallons to handle large domestic hot water needs. When using tankless gas water heater most homes would require 180,000 btu or even 199,900 btu and if installing one of these you might need to upgrade your gas supply line and this would be a extra cost. also when having a boiler and tgwh you need to vent two appliances and if the boiler and tgwh are venting sidewall sometimes you run out of places to vent these units. TT smart indirect water heaters have a lifetime warranty in residential use and most tgwh have a 12 year warranty on the heat exchanger and 5 year on parts. if you are going with tgwh make sure you do not have hard water or the unit will build up with lime hardness and clog the unit up. will have to get it pumped out. some times it needs to be pumped out every 6 months or it could last a year before you need to pump it out. please remember that if you have hard water and no water softener as the tgwh builds up with lime you will be using more gas making your gas bills go up to make domestic hot water. You could install a 3M cuno aquapure AP430 filter and this unit will keep the tankles gas water heater from building up with lime. It does not soften the water. filter needs to be replaced 2 to 3 times per year depending on how mush domestic hot water is used. hope this info helps
  • hot_rod
    hot_rod Member Posts: 22,107
    how much HW and how quickly

    do you need it? in many cases small storage systems mentioned above will provide plenty of DHW. Typically they allow you to run a couple faucets at once. Families with large dump loads, like soaking tubs, or back to back showers all in one time period might be better served with a tank style or a larger indirect run from the boiler.



    Any way to determine how much hot water you currently use?



    hr
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    I don't think combi units are usually a good choice.

    to generate 3 GPM of domestic continuously takes a lot of BTUs.



    Most homes with DHW loads that low don't need anywhere near the BTU rating of those boilers, and in fact are often near the "minimum modulation rate" of the boiler for a max heating load. In other words, they are oversized for the heating loads. And thus, less efficient.



    I'd rather size the boiler for the heating load. That's typically far more important from an efficiency standpoint. Then you could use an indirect sized for your DHW load. That will typically be the most efficient and cost effective route to go. You might get a bit more efficient with a high end on demand, but it would add significant expense.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I'd rather size the boiler for the heating load.

    My system has three zones, upstairs, downstairs, and indirect hot water heater. Hot water heater has highest priority. I got the smallest boiler in the product line (80,000 BTU/hr input) and that was somewhat more than my house requires. I do not use a lot of hot water; typically one shower and some hand and manual dishwashing. I also have a washing machine, but it usually runs on cold water (if the cold water is under 60F, it automatically blends in some hot). And a dish-washer that I run about once a week. Under these conditions, I believe the hot water runs between 5 and 10 minutes twice a day. Possibly three times a day (I am not sure if it runs overnight).



    I used to have an electric hot water heater that held 75 gallons. I needed that capacity at one time because the heater had a separate meter with a clock that cut it off from 4PM to 11PM or something like that. When peak power occurred in 1950.



    The indirect hot water heater holds a little under 40 gallons and that turns out to be adequate for me. But there is just one of me,  and I am not a teen-aged girl, so the water use is small.



    I once lived in a house in France (around 1950) that had a tankless water heater. While barely useful, I found it unsatisfactory. If I wanted very little hot water, I got none, because it would not come on at very low flow rates (e.g., hand washing). If it did come on, it took a while for the water to become hot, even though the heater was only a few feet from the tap. At low flow, the water was much too hot. At high flow, it was not high enough.



    I imagine tankless water heaters have made a lot of progress in the last 50 years. But I am biased against them. With my current system, I could put about 70,000 BTU/hr into that tank if necessary. I could not do it all day if I needed to heat the house too, but if it runs 1/2 hour a day, it would not affect the house very much.
  • hot_rod
    hot_rod Member Posts: 22,107
    size the boiler to the largest load

    and these days with super insulated, tight home showing loads below 10 BTU/sq.ft, it could be that the DHW load is the bigger load.



    Consider 1800 square feet of home with 8 BTU/ ft load at design = 14,400 BTU/ hr. That would be a slow recovery water heater input, less than a 4500w electric HW tank.



    So it may be a family of 4 with teenagers or a soaking tube would need to size the boiler/ heater to the bigger load, that being the DHW production



    I'm not a huge fan of high input tankless style heaters, but in a case like this I can see the attraction. Near endless DHW only when it is called for, might be better than waiting for a 14K boiler to recover 50- 80 gallons of DHW.



    It's nice to have so many DHW options. Tankless, small flash tanks in boilers, plate HX, storage vessels condensing or non, heat pumps water heaters, etc,



    I'm of the opinion every home should have a solar pre-heat component. 50-60% SF solar fraction, is do-able anywhere in the US.



    hr
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Vad
    Vad Member Posts: 55
    number of BTU required

    Thank a lot to all of you!

    I really appreciate your help.



        I would love to have a high efficiency boiler installed but I was told that since my house is too old (1925) I will have to spend extra thousands of dollars for the installation to adapt chimney and whatever else. Couple of professionals I invited told me that. It is a pity..

        I will describe my house in NY.. It has 1700sqf on 2 floors (about 850 sqf for each floor) + about 850sqf for the basement. It is a 2 family house.

      Two  families of 4 are going to live in the house.

        Each floor has a shower and a tube. Basement has a shower.

    There is a dishwasher on one floor and washing machine in a basement. There is a kitchen with hot water on each of the two floors and also a bathroom with a  hot water in the basement.

        From what I hear from you, it is more practical to have an indirect water heater. I will most likely follow your message.

            Now, how I would calculate a boiler size and a HWH sizes

        One person told me that I will need 175BTU boiler. the other one told that I will need 140BTU. The same person told that one 40 gallon tank will be enough (for indirect HWH). I currently have two 40 gallons, 15 years old direct HWH, one per each floor.

        I have no idea about heat loss as well.

        Is there any easy to understand reading available for all this staff?

        Solar pre-heat component sounds interesting but it is probably costly to buy and install.



       THank you,

    Regards,

    Vad
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Heat Loss.

    I agree with the professionals here who say you need to do a heat loss calculation.

    In fact, I guess one way to weed-out those contractors who are not qualified to install a high efficiency boiler is that they do not want to do one. As a homeowner, I would not want to replace a boiler without doing such a calculation, especially if you are doing a high-efficiency boiler, is because you cannot get the best efficiency withour such a calculation. With old style boilers, the penalty of using an oversized boiler was mainly the excess cost of installation, and the continuing excess cost of the unnecessary inefficiency.



    With an 1925 house, chances are good that it needs to be insulated, and high efficiency windows installed. Also leaks detected and fixed. This may get you more in increased efficiency than going from a low efficiency boiler to a high efficiency boiler. But if your house is 85 years old, this may have been done already.



    Calculation of heat loss is pretty easy, and there are even computer programs that help doing it. You can do it with pencil and paper if you choose. The hard part of figuring heat loss is that there are lots of tedious details where judgement is required, because it might be expensive to find out some of the numbers. E.g., is every space in the wall insulated?, What is it insulated with? How thick is the insulation? What outside temperature do you design for? (that one is fairly easy), ... A pro will probably have a laptop with him and could do it on the spot; I do not know if they do it that way though. He might fill out a form and take the numbers back to his office to do the calculations.



    The reason you need such a calculation done is it is just as bad to have an oversized boiler as an undersized one. I believe all high efficiency boilers these days are called modulating-condensing boilers. And the more oversized the boiler is, the less condensing you get. For example, in my house (smaller than yours and with no basement), where I live,a 155,000 BTU/hour boiler could probably modulate down to about 32,000 BTU/hr. Now my heat loss calculation that I did reveals that at 0F outside, 32,000 BTU/hr is the maximum amount I would need, so I would get no condensing at all. And actually, it is even worse than that because here, it would go under 14F only 2.5% of the time. So even though the boiler I have is rated at 93% efficiency, if I got one that oversized, the efficiency would probably drop to something like 87%.



    You just gotta get a heat loss done.
  • kcopp
    kcopp Member Posts: 4,431
    is this an apt?

    If this is i would opt for each unit to have its own electric water heater that they can be charged for their own water usage.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    not sure I agree with HR here.

    with sizing the boiler to the largest load.



    You can size a tank to meet the DHW load 9 times out of 10. no need to upsize the boiler untill you are done upsizing the tank. Granted, the tank upsizing may be more expensive by a bit, but until you hit 119 gallons, it's definitely the long term winner if it has any efficiency improvement on the boiler for heating loads.



    In most cases, never prioritize DHW efficiency over heating efficiency. they are almost always at least an order of magnitude apart in terms of yearly energy usage.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    I would Question

    Both those quotes. Need a heat loss to properly size the boiler. Vad, quick question. Is this fin-tube baseboard? If so, how many total feet? If you want to know which is quote is the closest to what you MAY NEED take the total footage and mult x 550. Be curious as to that number. This will atleast give you a rough estimate of what boiler size you should be looking for but you really need to have a heat loss done of the structure. 200' would be 110,000 btu's at a 1gpm flow rate and at the max it would give you 120,000 at a 4gpm flowrate. Is each floor it's own zone? If so do it by floor or zone.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    I'm so smart

    I said this and my very next estimate was for a 90kBTU heating system and 7 showerheads on a big family. Had to use two boilers or I'd have one 100k Boiler doing recharge on two 120 gallon tanks.



    Honestly, maybe I should stick with one, but I'm nervous about a 40 minute recharge after peak load. though with "priority switch" where it flips back to heating for awhile during long DHW demands, maybe that's not really a big deal.



    at least with staging we're not losing any efficiency for extra capacity. but i have to think adding the second tank would be more economical. hrmph.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    A McMansion

    Only has a heat loss of 90K? Your fibbing and testing HR's post. Who cares by the way that there are 7 shower heads. What's the usage in your ficticous home? 7 kids get in the shower all at once?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    First off

    Please don't call me a liar. I've never made up anything I've ever posted on.



    It's a multi-nozzle spray shower in a home with 4 full baths, and 8 total occupants, most of which are older children from two marriages. Safe to say all showers are going at once for a significant period of time in the morning most days.



    I still don't know how people actually use those multi-nozzle showers... do they really run multiple heads all at once? but until someone can answer that definitively... and I suspect it varies by client... I design for them all running.



    finally if you actually comprehended what you were reading, you would know that I was shooting down my OWN post... I had said "never upsize for the domestic load" and here I am, upsizing for the domestic load.



    But otherwise, great post! *golf clap*.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • mjcromp
    mjcromp Member Posts: 57
    other thoughts

    I like tankless (Rinnai in particular) and have installed many. One issue I'm starting to see more is with high efficiency appliances. They just inject a small amount of hot water at a time and some appliances it's not enough flow to turn on the heater. I have seen this in washing machines and dish washers.

    On another note I have installed the TT Excelence and have had no complaints with them at all!
    Too bad common sense isn't very common.
  • Jack
    Jack Member Posts: 1,047
    Minimum flow and input

    to initiate the Rinnai's operation has until recently been .6gpm and 15kbtu. The condensing and new V models now require .4gpm and 10kbtu. That is a significant improvement.
  • Vad
    Vad Member Posts: 55
    Looks like the boiler I am going to have is Burnham Series 2

    with the efficiency around 80%. My Clay flue chimney is old and I cannot use more efficient boiler.  I read recently that indirect water heater are especially efficient with high efficiency boilers. Do you think with the 80% efficient boiler I still get more efficiency with indirect compared with using regular direct water heater?



    Regarding the Heat loss, I calculated the amount of BTU needed (rough estimate) as I was told by multiplying baseboard length to 550 and I got about 57K BTU

    I will try to do the Heat Loss the right way. What is the best free tool I can use? I tried to find software on slantfin.com but looks like it is not available.

    Once I calculate a Heat Loss, How much BTU should I add for Indirect Water Heater. The other question. I currently have 2 Direct water heaters (15 years old) 40 gl each. Do you think 40 gl tank for Indirect water heating will be sufficient? (8 people, 2 showers, 1 washing mashine, 1 dishwasher)



    Thank you

    Vad
  • Wayne_16
    Wayne_16 Member Posts: 130
    Reuse of the old chimney?????

    If the chimney is very old, how solid is the inside?  Has anyone surveyed the integrity of the chimney?  Can the new chimney last the life of the new boiler?  Chimneys do deteriorate and fail.  They need to be inspected on the inside by a qualified person, looking at one from the outside will not tell if the integrity of the flue passage is sound.



    Once you know the inside condition of the chimney, this will help in your decision to what type of boiler to purchase.  If the condition of the chimney is such that is has to be replaced, relined etc. that is not cheap. 



    All chimneys need to be inspected periodically, more so as they age. 



    Minnesota Wayne
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    edited August 2010
    Heat loss ...

    "Regarding the Heat loss, I calculated the amount of BTU needed (rough

    estimate) as I was told by multiplying baseboard length to 550 ... "



    If you did that at my house (baseboard zone), you would get 28 x 550 = 15,400 BTU/hr.

    I calculated the heat loss up there to be about 6,250 BTU/hr.



    The reason for the considerable discrepancy is that I wanted to use water temperature up there as low as possible so my boiler would condense most of the time. The formula you give has two assumptions built into it.



    1.) You are running about 180F water through it.

    2.) The baseboard is the right size for the space.



    In my case, both of those assumptions are wrong.



    "How much BTU should I add for Indirect Water Heater."



    In my house, I made no allowance for the Indirect Water Heater. I had two reasons for that.



    1.) The Indirect Water Heater runs only about 1/2 hour a day, in two bursts of about 10 minutes each. I have no teenage girls here, and a 2 gpm shower head. The reason I say 1/2 hour is it may run once at night, and I do not know it.



    2.) My boiler is larger than I need, even though it is the smallest available in the product line.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Heat Loss/Boiler

    JD like I said in my above post this would give you a "rough" estimate. As we can see by the reply the boilers quoted to him were very very oversized. The btu's per foot are basic outputs with 180 degree water and the 1gpm and 4gpm flow rate. Without a heat loss this is the only way to shed light.

    Vad don't use the Series 2 boiler. If the added expense to line the chimmney is out of the budget the use the Series 3. Its 84% and has the option of adding an outdoor reset card to the boiler control. Burnham basically took the ES2 and put baffles in it to bring up the stack temp.

    http://www.usboiler.burnham.com/products/residential-boilers-indirect-water-heaters/series-3



    Do yourself a favor, add the reset card. Boiler can handle 110 degree return water temps. Simple rule of thumb is for every 3 degrees I can run my boiler below 180 degree water temp I can save 1 percent of fuel.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Vad
    Vad Member Posts: 55
    Not sure How good the chimney

    Nobody inspected it. It is probably not to important if high efficiency boiler is not installed.
  • Vad
    Vad Member Posts: 55
    I understand your case.

    In my case the water will be running a bit longer then 1/2 hour. How much BTU should I add to the boiler to support Indirect Hot Water Heater?



    Thank you
  • Vad
    Vad Member Posts: 55
    Thank you again to all of you

    I still have a question on



    1. how much BTU I have to add for Indirect Hot water Heater (8 people, 2 bathrooms with

        shower and tube, 1 dishwasher, 1 washing machine)

    2. If the boiler I use is 82% efficient, is it still make sense to use Indirect Hot water Heater

        or it is more efficient to use a direct HWH?

    3. I currently have two 15 years old direct HWH, 4oGl each. For indirect, one 40Gl will be 

        sufficient?



    The Plumber told me that he can reline the chimney for about fifteen hundreds. To my opinion it is not worth it since I can gain only 3% in boiler efficiency going from Burnham Series 2 to ES2. I can add about 5% efficiency added by Outdoor Reset. With maximum 8% gain, it will likely take me life of the boiler to recoup money I will spend for relining chimney. Am I right?

        Burnham S3 boiler is out of the picture since my gas company National Grid do not offer any rebate on it.



    Thank you,

    Vad
This discussion has been closed.