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  1. #1
    Join Date
    Aug 2005
    Posts
    3
    I thought this forum is only for HAC,some topic covered makes me think that maybe water heaters also enjoy experts here.
    If so,I am seaking advice on what to install for water heater:1 recirculation system versus tankless heater,versus convential gas water heater.
    This would be for a residence 3 bedroom house
    Thanks for any opinions and maybe recommended manufacturers or even pointers to another forum you might know of.

  2. #2
    I am considering the same move... from keeping 40 gal of water hot all the time to the tankless.... the main players are: Bosch, Tagaki, Rinnai. Bradford White also makes one as does Paloma.

    The main idea is to heat the water on demand.. turning on the hot water (around .8 gal per minute minimum) it activates the heater. When you shut off the hot water, the heater shuts off. Be careful with sizing so you have the capacity you want or need... too small and only one shower at a time and no wash. Also, there are elec and gas models... the elec have some mighty hefty amperage requirements, so check power availability. I am replacing LP unit and am going to stick with LP.

    The Bosch unit is a powered direct vent which appeals to me as it does not use conditioned room air and does not contribute to negative pressure in the house.

    Lots of info from mfgr sites... just google them.


  3. #3
    Join Date
    Sep 2004
    Posts
    654
    The tankless units I have seen are all electric and consume HUGE amounts of current, but only for a small amount time. The electric service in the house needs the capacity to handle this. Other than that issue and the expensive price of a good unit, the electric units seem pretty applicable for a wide range of uses, having no standby loss is big plus too.


  4. #4
    Join Date
    Sep 2004
    Posts
    3,157
    HUGE amounts of current, but only for a small amount time.

    --------------------------

    that would be , lets say 15 min shower for 3 of the 4 people in the home every day---with the amount of current needed to heat that water you could keep two 40 gallon water heaters going all the time .

    yes they do come in gas , both lp and nat

  5. #5
    Join Date
    Mar 2004
    Posts
    1,042
    I think they're really cool myself, but I did the math for my own home recently and found that the payback was a joke.

    We talk about standby losses, and the argument makes sense. Try turning off your water heater when you go on vacation for a few days. It'll still be hot when you get home.

    My household? Two people, energy star rated appliances, and a modern (2.5 gpm) showerhead. We have the fairly standard 40 gallon natural gas water heater. My gas consumption, which is for domestic hot water only except in the winter, is typically 13 therms a month. Figure a dollar a therm, and I am paying $13 a month.

    The energy factor of this water heater is probably around 0.60 (this basically means 60% efficiency, on the whole). New tankless units are typically 82%. So with my current unit, I am actually getting 13 therms * 60%, or 7.8 therms of energy in my hot water. To get the same amount of energy into my hot water with a tankless unit, I take my 7.8 therms and multiply by (1/82%); so a tankless would take 9.5 therms. That's 27% less gas. If my bill went down 27%, I'd save $3.51 a month on natural gas.

    Given the price difference and the general necessity for higher installation cost to put in a tankless (bigger electrical service and wiring for an electric unit, bigger flues and gas pipes for a gas unit) versus a regular unit, I don't see payback happening. If we assume the tankless unit costs just $300 more than a regular one and that it takes $300 extra to install one where you used to have a tank water heater, you need 170 months to break even.

    Maybe in new construction the math works better... or if you desperately need the space for something else.

  6. #6
    Join Date
    Jun 2004
    Posts
    146
    Originally posted by wyounger
    We talk about standby losses, and the argument makes sense. Try turning off your water heater when you go on vacation for a few days. It'll still be hot when you get home.
    A better experiment would be to leave it on and check the gas meter before and after your vacation. I did during my last vacation and found it using 0.2 therm/day while no hot water and no other gas appliance was being used. I suspect the average will be higher than that during the winter especially for people who have their hot water heater in unheated space.

    Originally posted by wyounger
    The energy factor of this water heater is probably around 0.60 (this basically means 60% efficiency, on the whole). New tankless units are typically 82%. So with my current unit, I am actually getting 13 therms * 60%, or 7.8 therms of energy in my hot water. To get the same amount of energy into my hot water with a tankless unit, I take my 7.8 therms and multiply by (1/82%); so a tankless would take 9.5 therms. That's 27% less gas. If my bill went down 27%, I'd save $3.51 a month on natural gas.
    Your calculation is really just the difference between 60% versus 82% efficiency and not really about tank versus tankless. If you add my figure of 0.2 therm/day standby loss, the monthly savings is about $10/month and higher during the winter. So it would make economic sense. What holds me back from committing to a tankless water heater is all of the other problems associated with it. The 2 main issues for me are: 1. you can't get a slow flow of hot water - most tankless water heaters won't heat unless the "hot" water flow is over 0.75 gallons/minute; and 2. if you momentarily shut off the hot water, you get cold water before you get hot water again which may surprise some people who are used to turning the hot water on and off with a tank water heater.

  7. #7
    Join Date
    Aug 2004
    Location
    Los Angeles, CALIFA
    Posts
    1,132

    Thumbs up

    Tankless water heaters really are the way to go. Fortunately I used to work for a Tankless water heater company as an engineer for a few years and was able to develop a pretty strong knowledge on these types of water heaters.
    Now when people think of Tank less water heaters they think that these are instantaneous water heaters. This is not true. These are on demand water heaters which means once a fixture is open the heater begins its heating process. So if you require instantaneous hot water then you would want to consider a re-circulation system. Now I do know that some brands you can use a recirculation system. But make sure that you get in touch with the manufacture and find out what size pump you may need. To be honest, most tank less water heaters have a very high head loss, so make sure you size your pump properly. You will want use a min- 1/12 horse power high head pump. If you have any questions please let me know. I will try to do my best without breaking the site rules.
    Do as I say, not as I do

  8. #8
    Join Date
    Jan 2005
    Location
    Bakersfield, CA
    Posts
    209
    tech, so which unit do you recommend? I am building a new home and the plumber wants to use Noritz. I had originally wanted to go with Bosch.

  9. #9
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    I just shut off the breaker to my 50g elec HWH -- turn it on 1- 1.5h before wanting to shower -- have yet to run out of 120F water while showering, even next day [ heater set at 140F, temp regulator installed for BA].

    but, I do most of other washing with cold water & soap --

    BTW, ProfessionalBuilder article states they figure 10- 15% savings with Bosch tankless.

    I noticed prices starting to drop for tankless -- ~$450 = elec.

  10. #10
    Join Date
    Nov 2001
    Posts
    1,874
    I'd stay away from the Bosch my self,
    I worked on some and they don't seem to hold up.

    Rinnai, has a good looking unit.
    If you try to fail, and succeed.
    Which have you done ?



  11. #11
    Join Date
    Nov 2001
    Posts
    1,874
    I'd stay away from the Bosch my self,
    I worked on some and they don't seem to hold up.

    Rinnai, has a good looking unit.
    I'd only worked the gas unit, don't know anything about electric ones.
    If you try to fail, and succeed.
    Which have you done ?



  12. #12
    Join Date
    Aug 2005
    Posts
    2


    I just finished installation of a Bosch Aquastar 250SX tankless waterheater(WH), gas (.8gpm activation flow, 6gal/min max flow:2 showerheads at a time. I choose this one because of the power vent, I decided to use the existing chimney for exhaust-through a 3" Z-Vent duct, the sealed combustion, no standing pilot and the high effiency-87% and 12 yrs warranty on the HX.
    During the summerdays (no heating) my gas bill was around $50 with the old(15 yrs) tank heater. Now it dropped to $28 having this one installed for only 15 days out of the whole month of billing.

    Advantages: endless hot water - was one of the reason I decided to use tankless, mounted on the chimney wall - use little space,sealed combustion, no maintenance.

    Disadvanteges: 1. activation flow (.8gpm) is too big so in order to have continuous HW we waste a lot of water even when we don't need. To be able to mix the HW/CW to have approx 100F without de-activating the WH, I changed the faucets around the house from the one lever type to two levers HW/CW type. This allows me to control better the amount of CW needed without de-activating the WH.
    2. Cost: xxxx WH + xxx Z-vent Stainless Steel vent+xxx new fixtures, etc.

    Bottom line : I was surprised about not being able to properly mix HW/CW without de-activation but I got used now. Let it flow...

  13. #13
    Join Date
    Feb 2004
    Location
    Central Kansas
    Posts
    1,145
    We install Noritz- seem to have a good warranty albeit I have not had to service one yet. Some things to consider, but many will not be a problem since this seems to be new construction. Unless you have a large garden tub and otherwise have needs for tons of hot water, I would do some serious math. It is easy to listen to a great
    American - Paul Harvey whom I have great respect for, and believe these are the greatest things since sliced bread.

    The honest truth is it is hard to pencil one out to justify if reducing fuel bills is the primary consideration. Again, if you need lots of continuous hot water- these babies may just what you need. Remember to buy one sized for the applications you will encounter. If you need capabilities of laundry, shower-after-shower, dishwashing all at the same time, buy the correct size. If not you will enjoy a nice, continuous supply of barely warm water.

    Most all of our installs have been commercial applications where lots of continuous supplies of hot water are needed. The initial cost of the appliance, added to the special venting requriements may likely not be overcome until the device wears out. Remember, these aren't your father's water heaters. They have numerous (moving) electro- mechanical parts. This means routine preventative service and eventual repairs. You can't put these babies in and ignore them like standard waters have been dealt with for decades. You also can't just turn on the tap and enjoy a quick shot of hot water to simply wash hands with. You will waste water waiting for warm temps and then after just a short run, assuming you need enough flow to activate the burners, will waste a lot of fuel for a little warm water.

    Now, if you are replacing an existing water heater... Combustion air- unless you pay more and I mean XXX more for a direct vented model, lots of combustion air is needed. These burn 189MBtu or more, not just 34MBtu+/-. The fuel line will likely need repiped- the line adequate for the old 34MBtu burner probably will not come close to cutting it for the tankless. Venting- the old 3" type B will not cut it, either. Lots of initial cost in a replacement to factor in. With even a 30% savings(real darn unlikely) lets see... My summer NG bills (water heating only) is about $19.00, including taxes, meter charges, etc. or about $9.00 in actual fuel charges. No, I do not get a gas company employee discount, for you who know my credential data.

    This confirms the $30 something/year mentioned earlier in savings. Now, I cheat a little, however. Or as Paul Harvey would say - the rest of the story. My condensing boiler with a Superstore indirect makes aaaalllll the hot water we need at 93-94% AFUE and we only have one teenager shower-master left at home. Your mileage may vary depending on driving conditions.

    I am not against these devices, like everything else they have their niche. If I were my own potential customer, I couldn't recommend one with a conscience. Even if I had a standard water heater, the math wouldn't add up. So, if you're building a new home- go hydronic radiant - you'll love it! Have them put in an indirect while they're at it. You will love that, too! Greg

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