Ridiculous gas bills with Naviens!!

Discussion in 'Tankless Water Heater Forum' started by molejn, Jan 5, 2010.

  1. molejn

    molejn New Member

    Messages:
    1
    Location:
    Seattle WA
    We have 2 navien units we installed side by side in our garage this summer to replace out hot water tank. We have a recirc pump set up and the temp set to 140 since the master bath is quite a distance from the Naviens. We are going thru over 300 gallons of propane in 7 weeks which is costing a fortune. Everything I read says that these things are supposed to be more efficient than hot water tanks. Our bills are twice what they were. Does any one have any idea why this is happening? I am ready to rip the suckers out and put in hot water tanks again!
  2. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    Turn the circ function off then or at least program to only run when needed.
    Hot water recirc by many could be considered a luxury, and it comes at a cost to keep that loop hot.

    Its not the heaters, but what you created is a constant heating loop all the way to the farthest point and then back. Depending on whether or not the supply and return pipes are insulated and how well only makes it worse.

    Putting a tank back in and still using recirc would be even worse energy costs. The difference in operating efficiency is about 15% so put the tanks in and use recirc and be prepared to buy even more propane.

    (Guys: note I said 10-15% versus using 30-40% which is commonly quoted. Remember the return temps are coming back elevated to be reheated, thus the unit is out of condensing mode and cycling besides, but without standby/flue loss calculated)
    Last edited: Jan 7, 2010
  3. AAnderson

    AAnderson In the Trades

    Messages:
    36
    Location:
    Aptos, CA
    It doesn't sound like you've ever programed the recirc function which would explain the high energy cost. Program this function for when you typically use hot water at the furthest point in the house. Insulate your hot water piping too.
  4. AAnderson

    AAnderson In the Trades

    Messages:
    36
    Location:
    Aptos, CA
    Why two Navien's? What is your total fixture demand?
  5. Runs with bison

    Runs with bison Member

    Messages:
    897
    Location:
    Midwest
    I would expect ridiculous costs with constant recirc.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,262
    Location:
    New England
    To make that more ecconomical you'd need a buffer tank. My guess is that the way you have this with the water returning, the thing needs to run essentially constantly. Doing this you'll probably also void the warranty. There are ways to make this more efficient. You'd need to read the user manual to see what they recommend when recirculation is installed.

    In some places, having 140-degree water circulating would be illegal in a residence. The potential for a burn incident is too high. Many places require a mixing valve to limit the max to 120-degrees, regardless of the input temperature.
  7. Dana

    Dana In the trades

    Messages:
    2,982
    Location:
    01609
    I don't get why you'd want or need 140F in combination with recirculation under any circumstances, but it's pretty much guaranteeing the highest possible parasitic heat losses. And if it's less than 100' each way to the remote tap the recirculation burns are all short-cycles too. It'll only get to 95% efficiency is when

    A: The water entering the heater is under 100F, and

    B: You're pumping more than 5-6 gallons through it per burn at somewhere around 1/4-1/3 of full-fire.

    Short-cycling it with 2 gallon burns @ 130F return water it's probably getting 50-60% net efficiency at the heater, before distribution losses.

    Then, considering you probably didn't insulate the plumbing runs to more than R2 (if at all) on the distribution/recirculation path your heat loss from that path is HUGE. I don't even run the tubing on my radiant heating over 130F- EVER, and it's doing a pretty good job of keeping the place warm. Your recirculation plumbing is just a long skinny heating radiator.

    If you plunked down a tank in the same spot, at the same temperature, with the same recirculation scheme, you won't save more than a dime or two in operational cost, and it may be a dime or two the other direction. With a tank heater you get an ~80% efficient burner but standby losses that take it way down, and if you're dumping all that standby heat to the garage, so you don't even get the heating-season benefit. You'd still have the huge distribution loss of all of that hot pipe hanging out there.

    Crank the temp down to whatever the hottest you'd need (probably 115-120F, to fill a big tub.) Run the recirculation on a demand basis, not continuous, and insulate the plumbing to at least R4 (5/8" wall closed cell foam), but R6 or more is better. (Some plumbing supply houses may have 3/4-1" wall closed cell foam pipe insulation, box stores won't. Grainger carries some selection too.)

    Also, 2 Naviens? Do you need to fill a big spa at 8gpm at the same time that 3 showers are going elsewhere in the house or something? (That's a heluva lot of burner there!)
  8. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    You should pipe the recirc through a little electric hwt that takes care of the minute heating. Not the tankless units. A nice little 120v corded 2 gal tank works perfect.

    [​IMG]

    http://www.bradfordwhite.com/products2.asp?id=3&product_id=18
  9. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    Why would heating water with a 120v tank be cheaper than heating it with a tankless if the tankless units are so efficient? Nice pvc relief line:eek:
  10. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    Because the tankless units aren't super efficient when they're heating water up 10 or 20 degrees. Any gas heating appliance with a low run fraction are terribly inefficient. You don't know this? A condensing appliance actually needs to be condensing to get it's super efficient ratings.

    The electric tank is very efficient all the time...
  11. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    Ah the navien units i've seen have their own integral buffer tank and the Factory set it up to be used without an outside tank. I suppose thats a design flaw that should be avoided by the consumer. In the pic of that rinnai what if you happened to be standing at the rinnai looking down when the relief valve for the small electric heater's relief decided to blow? Maybe a face full of 212 h2o? Not that uncommon either with a stuck thermostat. Becareful!
    Last edited: Jan 8, 2010
  12. Scott D. Plumber

    Scott D. Plumber In the Trades

    Messages:
    67
    Metlund!

    I agree with this an other posts. Constant recirc in a house is begging for high bills with any hot water source, not just Naviens.

    Look at this pump set up and switch your system out to it!

    www.gothotwater.com

    From what you say, it will be paid for in the first year!

    you want a circ system to help you not wait for hot water and to save water, but NOT EAT YOU OUT OF THE HOUSE WITH ENERGY COST!

    This is how you do it.
  13. Nice job....

    THAT IS REALLY A NICE LOOKING SYSTEM...except for the pressure relief
    drain pipes.....


    but I would hate to be the fellow that has to fool with and service it someday

    It amazes me what folks will go through just to get a tankless system
    and then realize they dont have instant and hot water and have to add that storage tank underneath it,,,,
    and then they find out they have to de-ime it every 6 months
    and it goes on and on from there.....


    but on the bright side,
    look at all the extra space you have now
    over a common tank type heater!!! LOL:D:D..


    ...



    ..

    Last edited: Jan 9, 2010
  14. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,037
    Location:
    Cave Creek, Arizona
    relief valves

    Someone must not have read where you should not connect multiple relief valve discharges together, especially if the size is not increased. And what is the deal with the "vent" which is where the water will overflow if either valve discharges.
  15. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    If your talking about the rinnai pic then its not a vent ,its for the condensate line from the tankless vent. 1 temp/pressure relief,1 pressure relief and 1 condensate drain all ito the same 3/4 PVC pipe. Wrong type pipe too. Here the pressure and temp valve would have had to go out seperate.
    The recir loops not insulated also,since we are talking about saving energy.
  16. Scott D. Plumber

    Scott D. Plumber In the Trades

    Messages:
    67
    The little tank is still not the best answer

    Why? Because of the heating elements and the timer. If the timer is "on" and the circ pump is "on" and you are running water around an uninsulated loop for 15minutes at a time, guess what else is "on"? THe elements! at what 1000w? 1500w? Thats like 25 light bulbs.

    Tankless water heaters are not "Instant" water heaters! If you want "instant" you need some kind of recirc unit. THe ACT Metlund is the best thing going right now for residential application in my opinion for any hot water system and for the same reasons. Solve one problem without creating more.

    BTW, if you have to delime every 6 months, you have other problems. you need a softener system. If you had a tank on that same rotten water, it would probably only last a few years, and if it were electric you'd have constant element issues. so nice try. At least you CAN delime a tankless.
  17. Runs with bison

    Runs with bison Member

    Messages:
    897
    Location:
    Midwest
    Electric resistance heating is never very efficient when you draw the box properly. Sure you can have a well insulated tank with what appears to be very high efficiency, but generation of electricity is much less thermodynamically efficient than simply burning the fuel to create low level heat in the first place.

    The above is why electric resistance water heating costs so much more than natural gas in most places. If you have nuke, wind, or hydro your electric cost will be much lower but for coal and natural gas the thermal efficiency is poor.

    By putting in the electric water heater the operating cost advantages of the tankless have just been lost.
  18. Central Coastal

    Central Coastal New Member

    Messages:
    1
    Location:
    California Central Coast
    Most likely recirc settings

    We replaced a tank unit with a Navien CR-240A about a month ago and was shocked to find our gas usage has now doubled! :eek:

    Turns out the remote controller was not installed AND the unit was set to external recirculation. So, the unit has been recirculating 24/7 all this time. :mad:

    After installing and programming the remote controller the unit only kicks on during usage and recirculating periods (as expected). Should see a huge difference in gas usage... hopefully. ;)
  19. Scott D. Plumber

    Scott D. Plumber In the Trades

    Messages:
    67
    Who installed it?

    My Question is who installed it? Were they trained? Did you DIY it to save money?

    If you paid an installing trained and licensed contractor you should have a chat with them.

    If you did it yourself...that's why you should have hired a trained and licensed contractor.

    Other installation errors can shorten the life of the product as well as cost you money on energy or be hazardous.

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