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  1. #1
    Join Date
    Jan 2008
    Location
    Ottawa, Canada
    Posts
    167

    instantaneous hot water heaters

    Are they all they're cracked up to be? I deal mostly on the commercial side of things so I don't know much about these hot water heaters. I've recently purchased a home with oil heating, I'm changing everything out for gas, including the hot water tank. Was thinking of going to an 80 000 btu instantaneous for my hot water. Is it worth it if I'm only using for my domestic hot water needs? Are they all that the sales say they're cracked up to be? All the hot water you can use without running out? Will I save that much on gas compared to your average 40 000 btu hot water tank. Do I need a circulating loop on the hot water side or can I go cold in, hot out without a loop? What are the best brands? Thanks guys.

  2. #2
    Join Date
    Dec 2007
    Posts
    12

    tankless

    when they mention endless water you must keep an eye on the capacity, most companies rate their heaters at 45 degree temperature rise and yes you will have endless water at the rated gpm with the rated temp rise ( 4pgm @ 45 degree rise) means if you have incoming water at 50 degres, you will get 4 gpm @ 95 degree water , if you raised the temperature your gpm goes down

  3. #3
    Join Date
    Mar 2008
    Location
    Taunton, MA
    Posts
    93
    the people who had them installed around here seem to think they're great, and around here the gas companies are giving rebate installing them

  4. #4
    Join Date
    Mar 2003
    Posts
    7,326
    Take a look at the condensing boilers assuming you have hot water baseboard. There ares some that have an integral heat exchanger for domestic, and others that are set up for a mega store tank. nice setup, energy efficient.

  5. #5
    Join Date
    Jan 2008
    Location
    Ottawa, Canada
    Posts
    167
    No baseboards, I would strictly be using it for domestic hot water purposes, no heating at all. Starting to think I should stick with the regular old hot water tank.

  6. #6
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,795
    In operation, the instantaneous will save you money. No stand by loss.
    Water conditions can effect them worse then a tank water heater though.
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  7. #7
    Join Date
    Nov 2003
    Location
    northern mass
    Posts
    411
    They work great. After water off all day, not a real warm day either, 5.5 seconds later had to pull the hand out from the stream of water.
    The heater only works when there is a call for hot water, thereby only spending gas when needed. A traditional hot water tank keeps temp, so it will be burning fuel when there is no call for hot water to keep the XXXgallons of water it has at whatever temp you set it at.
    An instantaneous won't run out on you, where a traditional evenually will.....for exampl long showers etc.

  8. #8
    Join Date
    Mar 2008
    Location
    Long Beach, CA
    Posts
    3,742
    The tankless water heater was introduced to appeal to those who have run out of hot water in the shower. The thought of endless hot water and not paying for standby loss all while being “energy efficient” has caught the attention of many. It has also created an industry of manufacturers and installers who, IMO, perpetrate a myth. I’ll explain.

    There are two components to a hot water bill. Standby costs and usage costs. It would be safe to say that standby costs amounts to about $10 - $15/mo. Usage costs would be whatever you happen to consume. The big question is; can a tankless, which are up to 380,000btu’s, heat water more cost affectively and efficiently than a slower 40,000btu tank type.

    When a unit has about 4 seconds to heat water 50 degrees, there has to be waist due to excessive heat and blow-by, in the way a car, plane, or jet loses mileage (efficiency) as it increases speed. There is a time dynamic to the efficiency formula that makes it seem impossible. Furthermore, I’ve never seen an owner or contractor report or show evidence of savings after the fact.

    Even if the unit was as efficient as the tank type at heating water, how long would it take to recoup the thousands spent at $15/mo? Answer; about 11 years if you don’t take longer showers. And, after 11 years you'll be replacing it due to life expectancy.

    Reasons to use a tankless are to gain closet space or have endless hot water, not to save money.

    Brian
    Last edited by Brian GC; 04-02-2008 at 02:32 AM. Reason: clarification

  9. #9
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,432

    Question Appropriate Comparison

    Quote Originally Posted by CDNtech View Post
    Are they all they're cracked up to be?

    Was thinking of going to an 80 000 btu instantaneous for my hot water.

    Is it worth it if I'm only using for my domestic hot water needs?

    Will I save that much on gas compared to your average 40 000 btu hot water tank.
    Gas might cost more than
    Heat Pump on a a 95% Efficient HWT.

    http://www.nyletherm.com/waterheating.htm
    or similar

    Gas rate ?
    Electric Rate?
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  10. #10
    Join Date
    Mar 2008
    Posts
    21

    Smile

    We have had a Rinnai tankless for 2 years now..I would not go back to a tank. You have digital temp control which is nice and unlimited supply. Mine is 188k BTU and I am on Geo so my desuperheater will be hooked up soon providing free hot water to preheat the tankless. Just keep in mind nobody points out the fact that the life expectancy can be at least twice that of a tank depending on your water quality maybe more since there is no tank to fail. Also the cost of power vent gas tank heater is not that much cheaper than a decent tankless. My last house had 50 gallon natural gas. My summertime gas cost three years ago( no furnace just hot water) was higher than my use now on tankless with two kids since that time(alot more usage). One other myth is the multiple use tale that you run out if you use more than a shower. Completely untrue. Mine will fire 8.5 gpm and easily handle two showers and a dishwasher at the same time. I hear from friends how they run out of hot before the garden tub is full or it just makes it and no hot left. No problem with these. Just do your research and look at YOUR needs, no one elses... Bottom line fact.... The tankless will save you money in the long run and they offer alot of convenience as well. Every thing negative that I ever read on these posts seems to come from people that have never owned one.

  11. #11
    Join Date
    Aug 2007
    Location
    ky
    Posts
    181
    Quote Originally Posted by Brian GC View Post
    The tankless water heater was introduced to appeal to those who have run out of hot water in the shower. The thought of endless hot water and not paying for standby loss all while being “energy efficient” has caught the attention of many. It has also created an industry of manufacturers and installers who, IMO, perpetrate a myth. I’ll explain.

    There are two components to a hot water bill. Standby costs and usage costs. It would be safe to say that standby costs amounts to about $10 - $15/mo. Usage costs would be whatever you happen to consume. The big question is; can a tankless, which are up to 380,000btu’s, heat water more cost affectively and efficiently than a slower 40,000btu tank type.

    When a unit has about 4 seconds to heat water 50 degrees, there has to be waist due to excessive heat and blow-by, in the way a car, plane, or jet loses mileage (efficiency) as it increases speed. There is a time dynamic to the efficiency formula that makes it seem impossible. Furthermore, I’ve never seen an owner or contractor report or show evidence of savings after the fact.

    Even if the unit was as efficient as the tank type at heating water, how long would it take to recoup the thousands spent at $15/mo? Answer; about 11 years if you don’t take longer showers. And, after 11 years you'll be replacing it due to life expectancy.

    Reasons to use a tankless are to gain closet space or have endless hot water, not to save money.

    Brian

    You beat me to it

    The new water heater tank has a pretty good Insulation. so standing loss is alot less that what it used to be.
    Though gas water heater standing heat loss is larger than electric because of the Heat exchanger cannot be insulated
    Reason to do it should be space and continuos hot water .(Only if your supply don't drop below the Temp rise spec of the tankless)

    Money saving would be very hard to justify.

  12. #12
    Join Date
    Mar 2008
    Location
    N Texas
    Posts
    69
    Quote Originally Posted by CDNtech View Post
    Are they all they're cracked up to be? I deal mostly on the commercial side of things so I don't know much about these hot water heaters. I've recently purchased a home with oil heating, I'm changing everything out for gas, including the hot water tank. Was thinking of going to an 80 000 btu instantaneous for my hot water. Is it worth it if I'm only using for my domestic hot water needs? Are they all that the sales say they're cracked up to be? All the hot water you can use without running out? Will I save that much on gas compared to your average 40 000 btu hot water tank. Do I need a circulating loop on the hot water side or can I go cold in, hot out without a loop? What are the best brands? Thanks guys.
    My $.02 -- and I am a plumber. Depending on heater location your hot water will not (probably not) be "instant" -- but will be "endless". There is a difference. Instant hot water supplies generally require circulation pumps and tankless systems not suited for this, and may reduce warranties. Tankless operates based on demand (water flow) 80K BTUH operating will not provide much capacity (??GPM@40-50 deg rise) and probably not satisfy whole house demands. You will get more hot water in summer than winter, because incoming water temp is is higher. Most probably you will need +/- 200K - 250K BTUH capacity for whole house. That's a lot of gas! Gas supplies may have to be upgraded. Electric models are out of the question!!!
    Will it save $$$ -- Maybe. Only if you use it with common sense. If we have endless supply of anything we tend to use more of it. With endless supply of hot water you may loose teenagers for days in the shower. Big bathtubs are legitimate. You tend to run out of hot water with 50 gal tanks, especially if other demands are placed on source at the same time -- but 75 gal tank can generally take care of this w/o much more initial or operating cost. I sell and install tankless all the time, but my feelings are mixed.
    Two showers and dishwasher are not accurate comparison -- try showers and/or tubs and 30 gal washing clothes at the same time. Dishwashers don't take much water.

  13. #13
    Join Date
    Mar 2008
    Posts
    21

    Thumbs up

    There is alot of talk of BTU. Nobody in these posts mentions that the unit only uses the BTUs required for the situation. My Rinnai runs 15k to 199K BTU after checking the spec sheet. It will not call up 199K BTU unless you are pushing the max which is 8.5 GPM on my unit. The rise will effect the top end but with a family of four and guests, mine has never had an issue with two or three simaltaneous uses. I have on the other hand run low or out with a 50 gas at my old house. I have been nothing but pleased with mine and as long as you stick with quality you can't go wrong IMO. It is true that you will need a 1 inch gas line to the unit in mst cases and there are some venting limits both horizontal and vertical. The ideal install is outside wall direct out band joist. The vent extensions are a bit pricey plus vertical install requires condensation kit. Good luck.

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