Rheem 21v40-7 -vs- Rinnai

Discussion in 'Tankless Water Heater Forum' started by gvplumber, Jun 26, 2008.

  1. gvplumber

    gvplumber New Member

    Jun 26, 2008
    One of my two Rheem 21V40-7, 40 gallon water heaters is dead... gone... kaput!
    Should I replace it with another of the same make and model or should I go with a Rinnai tankless?
    There are five people in my family who love long showers so this issue is putting a cramp on many.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    It depends on where you live and your expectations how well a tankless works. They need to be bigger if your winter water temps are low, and bigger yet if multiple things will be running at once. Then, if you water quality isn't great, you need to clean out the mineral deposits from it (like a teapot), or it will get all crudded up. It requires a large gas supply, so yo umay need to upgrade your service and the flue pipe (SS), is expensive, and hopefully, you won't need much to vent it outside. If you search, you'll find all sorts of comments on tankless, most not so good, an occasional lover...as I said, it depends on your expectations and physical plant. The standby losses from a good tank-type aren't all that bad, but the heating efficiency of a tankless might be lower; depends on the model. Also note if you want a trickle of hot water, a tankless may not turn on (this would apply to warm as well as a trickle of hot). Increase th eflow just a little, and then poof, it's too hot.
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  4. Gary Swart

    Gary Swart In the Trades

    Sep 1, 2004
    Yakima WA
    There have been studies that show tankless water heater are more expensive in the long run than regular heaters. This includes initial cost, operating costs, repairs, and life expectancy of tankless heaters. Those promoting tankless don't give the full picture. Personally, I hope that someday technology will provide the means to produce a cost effective unit, but that day isn't here yet.
  5. Master Plumber Mark

    Master Plumber Mark Master Plumber

    Feb 6, 2005
    Sensitivity trainer.. plumber of mens souls
    indianapolis indiana - land of the free, home of
    why not a 75 gallon???

    If you have two 40 gallon heaters tied together
    why not beat the other one to the punch before it
    goes out and just change them both out

    and install a 75 gallon gas heater...
  6. mrpedal

    mrpedal New Member

    Sep 26, 2007
    When we needed to relocate our 14yr old tank, I did some research and went with a takagi tk-3. It's been about a year now, and I like it, but as mentioned there are some pro/cons. Marketing would have you believe all sorts of things. Here's my (non-professional) observations:

    • We bought an external temp controller that lets you set the temp in 2-3degree increments. We set it to 113F, and turn the shower on full hot and it's perfect. The controller is like a thermostat size, and I plan on moving it up into a closet in the bathroom for easy adjustment (IE: upping for a bath, clothes/dish washing). This bought us a little more gpm from the unit.
    • It's very quiet when running, and doesn't take much electricity. about 85w when working, i think 10 or so when waiting. Obviously no gas use when not running.
    • It's really small (takagi TK-3). We got some good space back from the loc of the old tank and it's plumbing, plus a bonus closest space when we took out the exhaust flue.
    • we can now fill the bathtub and not freeze when the 40gal tank is out.

    • # takes an extra bit for the kitchen sink water to get hot. 15sec maybe? This is the longest run in the house, and it took a long time even with the tank.
    • # First time the water was turned on, some debris lodged in our old plumbing (galvanized), and the flow rate was under the .4gpm needed to get the heater to kick on. So we had no hot water to the kitchen sink until I replaced that with copper.
    • # no h20 if power is out. Never happened, knock on wood, but still.
    • # Output fluctuates with seasons due to input water temp. Lowest I've seen is 55F comming in, which still gets us 5+gpm of water at 113F. Max of our unit is 7gpm, which we got in the summer when the water was 65-70F.Avg showerhead is 2.5ish, but a bathtub/washing machine will grab 5gpm easy. It does throttle volume not temp, so you won't get a cold water shocker if you exceed it's capacity, just less pressure.
    • # price. For the exterior takagi tk-3, and interior mount box, fancy flush valves and remote, it cost me 1100-1200 (don't remember exactly) for the parts. That's a couple tanks.
    • will prob need a larger gas line (1" will prob do it. Most houses have a 3/4". Bigger unit, running lots/bigger of gas apps at once might even need 1.25").
    • venting runs have to be <35 feet-ish, and the vent pipe isn't cheap. Outside install/unit choice helps with this. Gotta stay away from windows with that too.

    Some caveats/observations:
    • My main motivation was space. We live in the sf bay area, and are making the most of our 1700sqft living space. Between getting rid of the tank and flue (as well as a furnace and duct upgrade) we got a lot of space back.
    • It's just me and the wife (and the veritable B&B level of friends and family visiting all year), so our unit is rated for 7gpm on a 45deg rise. Translate that to 6.5-7gpm summer, and 4.5-5gpm winter, at 113F. We have 2 hot showers all the time. The incomming water temp doesn't usually dip below 50F though. That's not going to be the case on the east coast.
    • It's hard to quantify $$ savings and how long it would take to pay for itself due to our low usage profile.
    • I copied/pasted parts of this post from various other emails, so pardon the redundancy :)

    cliff notes: cons: upsized gas line, min flow & wait for hot, high price, poss $$ venting pro: endless hot, no standby loss, less space required

    Hard to comment on reliability in this time frame. Also, our water quality here is very good, so issues with clogged inlet filters haven't been a problem. I'll flush my unit this weekend and see how it's looking. 6months ago it was still perfect. If your water is not so clean, you could see much lower life for the unit.

    Last thing- I know many others with Rinnai units installed, and 0 complaints. Brand doesn't seem to matter much if it's a Noritz, Rinnai, or Takagi. But my sample size is small, so ymmv. Ask a *real* plumber who buys a 10-20 pack of one brand, not some yahoo on the net doing odd jobs :D
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