(206) 949-5683, Top Rated Plumber, Seattle
Results 1 to 7 of 7

Thread: Which is more efficient--one large WH or two smaller ones?

  1. #1
    DIY Junior Member queen50's Avatar
    Join Date
    Mar 2012
    Location
    Washington state
    Posts
    16

    Default Which is more efficient--one large WH or two smaller ones?

    We need to replace our 40-gal electric WH. It shares a closet in the main floor bath with a washer & dryer. It was fine for two of us, but we added a basement bath last summer, and now have 7 people living here for the next two years or so.

    I can put a larger water heater in the space, but I don't want to pay to heat extra water after they leave.

    Would it be possible/advisable to put a second WH downstairs? The idea would be that the second WH would service the basement bath, but could be shut off when not needed. When off, the bath would be serviced by the main WH.

    Any suggestions?

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,446

    Default

    The standby losses of any water heater are dependent on several things: surface area, the differential temperature (water in the tank to the surrounding air), and the quality and quantity of insulation. Electric WH have typically lower standby losses than those with burners, since the burner and flue must be uninsulated. So, from a standby loss, a bigger single tank would be more efficient. Keep in mind that you only heat the water you use, so a bigger tank by itself won't have much more cost unless you draw more water from it and therefore have to heat more - IOW, keeping it hot isn't a big thing, and the standby losses of one big one would be less than two smaller ones.

    Shutting off and bypassing a WH can be done, but you'd want to probably drain the tank that was going to be unused for a long period otherwise, you'd end up with stagnant water that would likely grow some nasties in it. ANd, you'd probably want a lock-out on the circuit breaker to prevent someone from turning it on accidentally, since you'd burn out the elements in minutes if there were no water surrounding them.

    Having a second WH closer to the point of use will mean hot water faster, so that's a good thing, but the addition of a hot water recirculation system would make it faster still, even from one point.

    There are probably other pros and cons, and certainly opinions. See what others have to say. Basically, you can do it either way. You can also make any WH have a larger apparent volume if you raise the storage temperature and use a tempering valve on it's outlet to limit the outlet temperature to a safe value (generally considered to be 120-degrees max for a residence). Say, run the WH at 180 and after mixing, you'd have lots more water at 120 than you would if the tank started out at 120.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Master Plumber master plumber mark's Avatar
    Join Date
    Feb 2005
    Location
    indianapolis indiana - land of the free, home of the brave....
    Posts
    4,244
    Blog Entries
    1

    Default if you have the room

    if you have the room, why not just install a 65 or
    80 gallon electric water heater and blanket the unit.....

    there is no reason to install another heater next to the 40
    they will just be trying to heat the area where they sit..including .
    the plumbing and electrical work that would have to be done.....

    go big with 7 people,,, install a blanket on the unit, install it in a
    drain pan... do the thermal expansion tank and live happly ever after.


  4. #4
    DIY Senior Member JerryR's Avatar
    Join Date
    Jul 2011
    Location
    Florida
    Posts
    192

    Default

    Look at this thread. http://www.terrylove.com/forums/show...er-tempering-)

    A mixing valve will give you 60 gallon performance from a 40 gallon tank. I went this way because my 50 gallon tank would run out of hot water before filling the roman tub. Now we never run out of hot water.

    Set the water heater to 140 dF and set the valve to supply the house with 120 dF.

    JR
    Last edited by JerryR; 04-03-2014 at 07:34 AM.
    JR

  5. #5
    Master Plumber Caduceus's Avatar
    Join Date
    Oct 2013
    Location
    Pittsburgh, PA
    Posts
    99

    Default

    That link has some of the the most amazingly manipulative propaganda.

  6. #6
    DIY Member Wallijonn's Avatar
    Join Date
    Jun 2013
    Location
    Arizona
    Posts
    46

    Default

    Quote Originally Posted by queen50 View Post
    ... we added a basement bath last summer... I can put a larger water heater in the space, but I don't want to pay to heat extra water after they leave.
    I take it that you also installed the appropriate 20, 30 or 40 amp 240V breaker & wiring to the new WH?

    Consider the cost of electricity. Wouldn't two WHs cost more to heat?

    Most of the stickers on the larger WHs I've seen say that they will use more electricity (cost per year) than smaller units and have a lower efficiency rating. Wouldn't setting the thermostat to 140F cause it to increase the cost of electricity exponentially? Let's say that you install a 80g WH. 2 years from now they move out. What then? Will you remove it and install a smaller WH? If you didn't live in WA. state I'd say to install a solar powered WH.

    Your best bet may be to install the mixing valve and raise the temperature. I will be installing fire brick under my WH to prevent heat losses drained out by the cold concrete at night. If you could apply fire brick to two sides (walls, and fire brick to the bottom, and install a thermal blanket, and also the mixing valve and expansion tank, your heat losses may be minimal and two years later when the basement occupants move out you can turn down the WH thermostat to reduce electricity costs.

    A refractory brick is built primarily to withstand high temperature, but will also usually have a low thermal conductivity for greater energy efficiency.
    http://en.wikipedia.org/wiki/Fire_brick
    Last edited by Wallijonn; Today at 07:26 AM.

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,446

    Default

    A bigger tank lists for a higher annual energy use partly because it is expected to source more hot water! Especially on electric tanks without a flue up the middle and uninsulated bottoms (for the burner), raising them off the floor isn't a big deal. Also, keep in mind that the volume of a tank goes up faster than the surface area, and surface area is where the heat loss occurs.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

Similar Threads

  1. Connecting smaller bathroom sink drain to a large P-trap?
    By Bratan in forum Shower & bathtub Forum & Blog
    Replies: 2
    Last Post: 05-04-2013, 05:58 AM
  2. Help! Need Smaller and Flush Friendly
    By JGM in forum Toilet Forum discussions
    Replies: 1
    Last Post: 08-04-2012, 03:48 PM
  3. what tool do you use to clean smaller pipes?
    By Pipe7000 in forum Drain Cleaning
    Replies: 7
    Last Post: 02-22-2010, 07:00 AM
  4. Smaller sheets of drywall
    By Ian Gills in forum Remodel Forum & Blog
    Replies: 8
    Last Post: 11-17-2009, 09:26 AM
  5. Water spot smaller with new hardware?
    By RallyJon in forum Toilet Forum discussions
    Replies: 5
    Last Post: 10-30-2005, 11:49 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •