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RINNAI TANKLESS WATER HEATER?

Post in 'The Green Room' started by Todd, Feb 27, 2007.

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  1. Todd

    Todd Minister of Fire

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    Just received a bid for installing a Rinnai 2520 FFU tankless gas water heater. This unit is capable of providing endless hot water at approx 4.2 gal per minute. Warranties: ten year heat exchanger and five year on other parts. Cost $2250.00.

    Kind of costly, but uses less gas and we won't run out of warm water. Does this seem like a reasonable installation price?

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  2. sailor61

    sailor61 Burning Hunk

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    I can't respond to the specifics of a Rinnai but I can tell you about my parents' experience with a tankless demand system about 10 years back.

    Everything you read about the energy savings, and endless supply of hot water is true.

    The problems came in when they would want enough hot water to wash their hands etc. Their unit was installed about 10 years back - in order for the burner to light up the flow had to be fairly significant - it was almost impossible to get a small quantity or low flow of hot water. Additionally. getting it serviced was an issue. The local gas company didn't want anything to do with repairs. After a few years they went back to a traditional tank. Don't get me wrong, the tankless demand was WONDERFUL for showers, baths, laundry - anywhere you needed a constant, fairly large, supply of hot water. The real let down was at the sink-

    I would guess that the designs have improved in intervening years but as a soon-to-be fellow Fireview owner felt I needed to pass on my experience.

    When remodeling my own home I considered a tankless but went another route.
    I have an indirect tank run off my furnace and find it to be a midpoint between the various options. I benefit from the efficiency of my furnace compared to a water heater and have the luxury of low flow hot water. On the other hand I live with a higher energy cost than a tankless direct would be.
  3. TMonter

    TMonter Minister of Fire

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    You'll never see a return on the tankless unit at that price in less than 15 years. The cost difference between a tank-type unit and a tankless is too great. If you need the endless hot water it's not bad, if you don't I have some other suggestions for you.
  4. Corey

    Corey Minister of Fire

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    I looked into some a few years ago. I don't remember all the spec's but the thing that got me was the 'delta T' ...which is the amount they can warm up the water. They would be quoted at '3-4gpm' etc, but that was a dT of 40 or 50F. In the winter, our water is coming out of the tap around 40F, but taking a 80F shower seems almost frigid to me. To get a good temp rise, the flow had to be cut back to 1.5-2 gpm which was not enough to supply the show head...even the low flow ones.

    Not saying this is the same in your specific case, but often high advertized flow rates are for relatively low temperature rises.

    Corey
  5. TMonter

    TMonter Minister of Fire

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    From one of my previous posts:

    To compare here is my situation:

    I used on my old Tank-type heater on average 35 therms a month at $1.16 per therm. The old water heater had a new efficiency of 0.58

    When I looked at the Bosch Aquastar it was going to cost me about $1600 to install one and efficiency was 0.87

    A new tank-type heater with R-20 insulation and an efficiency of 0.64 was going to cost me $425

    So to do a direct comparison

    Delivered energy in the initial case was 35*100,000 or 3.5 million btu, actual usable energy was 3,500,000*0.58= 2,030,000

    With a Bosch Aquastar I would have to purchase 2.33 Million Btu of heat for the same amount of water. This is about 23.3 Therms

    With a Standard Tank type I need: 3.17 Million Btu of Heat delivered or 31.1 Therms

    So the monthly savings on a Tankless over a tank-type is: (31.1*$1.16)-(23.3*$1.16)= $9.048 per month or $108 per year

    Therefore to make up the cost of a tankless unit, assuming no repairs or problems with either unit, I would have to run the tankless unit at current prices for 11 years. That’s a long payback when I can put $1200 bucks in a mutual fund at a return of 8% average and in 11 years have $2800

    Tankless type heaters under most situations do not make sense financially.
  6. Todd

    Todd Minister of Fire

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    Thanks for the replys. It does seem that the pay back would take awhile, but don't tankless heaters last twice as long as tank? I heard tanks last about 10 years.
  7. TMonter

    TMonter Minister of Fire

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    Tanks last a long time if you maintain them. I replaced a 16 year old tank unit last year on my house. There are a lot of tricks to getting a tank unit to last a long time, one of them is adding a second anode rod into the tank before you install it. Also draining your tank yearly helps a lot as well.

    Most tank-type units fail because they are not maintained.
  8. Metal

    Metal Minister of Fire

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    Tankless are nice if you don't have much room for a tank. Some of the new models can even fit between 16" on center studs and can be recessed in the wall. Most people don't buy tankless to save money, they buy them because they have a huge bathtub to fill or a bunch of people wanting to take showers back-to-back and need the constant hot water or they don't have space for a tank (apartments). There is some maintenance on tankless as well, especially if you have hard water since the heat exchanger and internal parts can "lime" up. Your venting will also be more expensive on the higher efficiency models since they condense and therefore need special stainless steel or in Rinnai's case you can also get Ubbink vent which is made of aluminum and plastic. Some of the cheap models that aren't as efficient can be vented with regular B-Vent.
  9. mikeathens

    mikeathens New Member

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    Todd:

    I have a Bosch Aquastar 125 (I think) running on propane. It was in my house (new) when I bought it in '04. Like mentioned, I've noted that you can't just turn on a trickle and get hot water - there has to be substantial flow. We get out water froma a cistern, so our filters plug frequently. When taking a shower, if I don't keep the filters changed, the variation in pressure from the jet pump/pressure tank cycling combined with the increased pressure drop through the filters tend to shut off the flames in our tankless unit at the lowest tank gauge pressures (40 psi). I will be changing tankless unit out to a 12-year 40-gallon electric tank when I get the money - that will give us more consistency.

    If most of your other applicances are electric, you might want to consider going with electric hot water - on the other hand, if heat, stove, etc. are gas, probably want to stick with gas hot water.

    The Rinnai units are at least double the price of the Bosch units - I don't know if there are any benefits. Also, due to reasons above, I would verify that you can still get hot water even at low flows - might seem silly now, but just wait until you want to crack the tap for a trickle of hot water for an extended period. You'll soon become very annoyed (assuming that the Rinnai has the same characteristics as the Bosch), and you might see less of a savings because everything will have to be done with the tapp full open (= more cost for water/sewer).

    Also, electric will eliminate the need for an elaborate chimney system if it will be located in the basement.

    I am curious to see if any of the upper-end tankless units have some sort of microprocessor control to maintain consistent water temperatures at any flow. Also, wondering if any of the newer gas or electric models will work under "trickle" conditions.
  10. sailor61

    sailor61 Burning Hunk

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    Todd,

    curious what you decided to do for hot water?

    Tom
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