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Old 09-23-2010, 08:43 PM   #1
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Make the jump to tankless? Recommendations?


I got a plumber to do some work, including relocating a tank water heater. Now he is pushing tankless water heater, which I had thought about briefly but not seriously since it would be a lot of money that you do not earn back in energy savings for a long time. I am now finding out that the new location for the tank poses addition problems, so that's why plumber is pushing tankless.

One of the additional problem is that I really need a 50gal, instead of the 40 I currently have. Long story short, small house, space is tight, the extra ~6" could be a problem. The house is 2bath. One is toilet,single sink, tub/shower combo. The other is toilet, single sink, shower only. Plus kitchen (sink & dishwasher), and laundry. Is 50gal correct sizing?

If I do decide on tankless, plumber suggests mounting outdoors in the backyard. What are your opinions on outdoor TWH? Freezing temps is not an issue here, however, being close to the ocean, metal tends to rust VERY easily.

My only experience with tankless was not a pleasant one. Although I may be comparing apples and oranges. I was using a point of use electric water heater for a shower when I was vacationing in asia. You had to get the flow rate of the hot side exactly right, too low and the heater doesn't turn on, too high and it cant keep up with heating the water. I ended up having to take low pressure shower, and turn down the cold side so the heat can keep up. I hope the whole house ones are better. What size tankless would be needed for my house? What is the typical min flow to trigger the heater on?

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Old 09-24-2010, 06:40 AM   #2
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Make the jump to tankless? Recommendations?


Unless you like spending a lot of money with zero return and unless you like variable temperature water I suggest you keep what yo have.

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Old 09-24-2010, 08:19 AM   #3
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Make the jump to tankless? Recommendations?


I installed a tankless NG water heater in my home and I am very happy. The extra space is nice and I am seeing a decrease in gas consumption by comparing therm usage for the same time period over previous years.

It's easy to find out what size unit you need by filling out a usage survey at any manufacturer's website.

Most gas fired tankless units require approximately .4 gpm flow to fire. I have heard there are new models that will fire with any amount of flow.
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Old 09-24-2010, 10:43 AM   #4
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Make the jump to tankless? Recommendations?


I also have a tankless water heater. There are plusses and minuses. Smaller size can be a huge benefit, and it sounds like it would be in your case. I cannot comment on outside installation. Mine is inside.

Based on my experience, I don't think you have to worry about low flow rates. While it is true that a minimum flow is required, I have never experienced lack of hot water due to low flow. Depending on the capacity of the unit, high flow rates should not be a problem. I have never experienced lack of hot water due to overdemand.

The problems I HAVE experienced are varying hot water temperatures at instantaneous changes in demand. If one is in the shower and another turns on a second shower, it takes several seconds until the unit can begin producing higher quantities of hot water needed for the second shower. Until that time, the hot water in the first shower can be less hot. This also happens in reverse. If two showers are on and one is turned off, the hot water in the remaining shower can get hotter for a few seconds until the unit reacts to the reduced demand.

A second issue is that it takes a bit longer to get hot water than from a tank unit. It takes a few seconds for the unit to begin producing hot water. Compared to a tank unit where hot water is available instantly, the delay is noticable. If you have equipment (dishwashers for example) that rely on hot water to work well, you may find that you have to take precautions, such as running water at a faucet, to ensure hot water is immediately available at the equipment supply.

Regarding cost savings, I am skeptical. While I don't doubt that they use less energy, you will use more water (while waiting for the hot water to be available. More significantly, I understand that most tankless units require a higher degree of maintenance (annual flush) that far offsets any cost savings resulting from lower energy use. On the other hand, you will theoretically have to replace these less often than you would a tank version. I suppose if you are running a car wash or use a bazilliion gallons of water, you may save, but for a couple of people in a small house, I suspect you will be dissapointed with your overall cost savings.

Still, if space is a major consideration, I would definitely look at tankless units. Assuming it is sized properly, I don't believe you will be disappointed with the availability of hot water.
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Old 09-24-2010, 07:16 PM   #5
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Make the jump to tankless? Recommendations?


Quote:
Originally Posted by fabrk8r View Post
Most gas fired tankless units require approximately .4 gpm flow to fire. I have heard there are new models that will fire with any amount of flow.
how much exactly is .4gpm? A drip, a trickle, a small steady stream?


Does a tankless require a drain like a storage type does?
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Old 09-24-2010, 07:54 PM   #6
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Make the jump to tankless? Recommendations?


Quote:
Originally Posted by oberkc View Post
A second issue is that it takes a bit longer to get hot water than from a tank unit. It takes a few seconds for the unit to begin producing hot water. Compared to a tank unit where hot water is available instantly, the delay is noticable. If you have equipment (dishwashers for example) that rely on hot water to work well, you may find that you have to take precautions, such as running water at a faucet, to ensure hot water is immediately available at the equipment supply.
a recirculation system supposedly fixes that problem. But I don't know much about how that works.
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Old 09-24-2010, 09:06 PM   #7
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Make the jump to tankless? Recommendations?


Quote:
a recirculation system supposedly fixes that problem. But I don't know much about how that works.
True, so long as it gets the minimum flow rate required, but I have my doubts that this would be effective with a tankless system. I am not even sure such a pump is compatible with tankless. Furthermore, while you could circulate hot water, the unit would be producing hot water at a low flow rate. Then, when demand increased suddenly, there still remains that lag time that the unit takes to ramp up production. Besides, the major point of tankless is energy conservation. There goes your savings?

Quote:
how much exactly is .4gpm? A drip, a trickle, a small steady stream?
In case you don't recognize the unit, that means gallons per minute. O.4 gallons per minute. I would categorize that as more than a trickle. Get yourself a bucket and run water for a minute at a rate that fills just under a half gallon. Judge for yourself if you could live with that. I can and have been. It is not much.

Quote:
Does a tankless require a drain like a storage type does?
No. There is no tank, therefore no risk of vaporization of water, causing over-pressurization.

Last edited by oberkc; 09-24-2010 at 09:09 PM.
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Old 09-24-2010, 09:41 PM   #8
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Make the jump to tankless? Recommendations?


Quote:
Originally Posted by oberkc View Post
True, so long as it gets the minimum flow rate required, but I have my doubts that this would be effective with a tankless system. I am not even sure such a pump is compatible with tankless. Furthermore, while you could circulate hot water, the unit would be producing hot water at a low flow rate. Then, when demand increased suddenly, there still remains that lag time that the unit takes to ramp up production. Besides, the major point of tankless is energy conservation. There goes your savings?
makes sense, which is why i didn't understand how recirc system would work? It is simply what I read in related articles.

I think what they really need is a recirc system WITHIN the TWH, where a temp sensor on the output tests the water for the correct temp. If not hot enough, then recirc within itself to heat it again. The will correct the issue with cold temp on sudden demand, while the control circuit can have a little more time to catch up.
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Old 09-26-2010, 10:27 PM   #9
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Make the jump to tankless? Recommendations?


Quote:
Originally Posted by acerunner View Post
makes sense, which is why i didn't understand how recirc system would work? It is simply what I read in related articles.

I think what they really need is a recirc system WITHIN the TWH, where a temp sensor on the output tests the water for the correct temp. If not hot enough, then recirc within itself to heat it again. The will correct the issue with cold temp on sudden demand, while the control circuit can have a little more time to catch up.
TACO makes one that connects on the fixture farthest away from the hot water heater. You press the button and it circulates water from the hot side back through the cold water side until it senses hot water and then shuts off. I have a fixture 65 feet away so will be picking up the TACO soon. That's about the only complaint I have about tankless. My install.

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