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Old 02-22-2013, 11:00 AM   #16
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Tankless Water Heater Basics..


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Originally Posted by md2lgyk
The websites for companies selling tankless heaters have charts and such to help you figure out what size you need. I don't think oversized is a problem; it's undersized that will get you lukewarm water at times.

You mentioned submarine showers. Did you actually serve on a sub? I did, back in the 60s and 70s. SSBN-654.
No, I never served on a sub, but in searching this forum for info on tankless water heaters the sub shower came up in just about every thread. Thanks for your service btw.
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Old 02-22-2013, 11:23 AM   #17
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Tankless Water Heater Basics..


aricus......md2 summed it up pretty good...

What size tank do you have now? I have a 50 gal and we have never had an issue.

I'm in the same basic area and I've done a lot of research into the same subject. Some of the conclusions I've come to...

If you have an electric water heater....tankless is a good way to go over getting another electric tank heater.

A gas tankless has a much longer payback....by my estimates...about the time it's reached the end of it's life...your just starting to get a payback....except for the following.

If you use a big slug of hot water for just a short period of time...say in the morning....then basically, there is no hot water demand for several hours....then the payback starts to be there. Or, if you have more hot water demand than a tank heater can keep up with....

If you use hot water all day long like we do, a tankless does not have the payback.....I can buy 2 gas tank heaters for the cost of one tankless...and since they have a 12 year warranty (which means they last about 20 years)....the payback is not there.

If you go tankless gas....you will most likely need to upsize your gas supply....and I think your vent needs to be larger.....
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Old 02-22-2013, 11:47 AM   #18
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Tankless Water Heater Basics..


I just ran some heat balance numbers. This is interesting.

On a normal 50 gallon tank with a 40k btu/hr burner, with 120F outlet temp and 50F inlet, if you take a 30 minute shower (3 kids in a row or maybe 2 adults taking long ones) with a 2.5gpm flowrate, you'll have 90F water in the tank at the end of 30 minutes. I didn't take into account any heat from the tank material itself, so it would be higher because there is quite a bit of thermal mass there.
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Old 02-22-2013, 12:26 PM   #19
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Tankless Water Heater Basics..


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Originally Posted by ddawg16 View Post
aricus......md2 summed it up pretty good...

What size tank do you have now? I have a 50 gal and we have never had an issue.

I'm in the same basic area and I've done a lot of research into the same subject. Some of the conclusions I've come to...

If you have an electric water heater....tankless is a good way to go over getting another electric tank heater.

A gas tankless has a much longer payback....by my estimates...about the time it's reached the end of it's life...your just starting to get a payback....except for the following.

If you use a big slug of hot water for just a short period of time...say in the morning....then basically, there is no hot water demand for several hours....then the payback starts to be there. Or, if you have more hot water demand than a tank heater can keep up with....

If you use hot water all day long like we do, a tankless does not have the payback.....I can buy 2 gas tank heaters for the cost of one tankless...and since they have a 12 year warranty (which means they last about 20 years)....the payback is not there.

If you go tankless gas....you will most likely need to upsize your gas supply....and I think your vent needs to be larger.....
Excellent post. For our situation, I was lucky that the gas line was large enough already, I only needed a short vent kit to go through the wall, and I picked up a brand new Rinnai condensing for $900 shipped. Total cost for everything ended up being around $1200. I may eventually break even compared to a gas tank, but paying a little extra for the benefits we get out of it is worth it.
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Old 02-22-2013, 05:52 PM   #20
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Tankless Water Heater Basics..


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No, I never served on a sub, but in searching this forum for info on tankless water heaters the sub shower came up in just about every thread. Thanks for your service btw.
Thank you for that. While I did serve 8 years in the Navy, I eventually ended up retiring from the Air Force. Given the pension and medical benefits, it's one of the smartest things I've ever done.
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Old 02-22-2013, 05:53 PM   #21
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Tankless Water Heater Basics..


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No, I never served on a sub, but in searching this forum for info on tankless water heaters the sub shower came up in just about every thread. Thanks for your service btw.
Thank you for that. While I did serve 8 years in the Navy, I eventually ended up retiring from the Air Force. Given the pension and lifetime medical benefits, it's one of the smartest things I've ever done.
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