# Tell me about tankless water heaters
**URL:** https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835
**Category:** Factual Questions
**Created:** [March 18, 2008, 9:20pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835 "2008-03-18T21:20:52Z")
**Posts on this page:** 17
**Page:** 1
### Author:  [@Projammer](https://boards.straightdope.com/u/Projammer)
#### Post date: [March 18, 2008, 9:20pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/1 "2008-03-18T21:20:52Z")
The water heater in my home seems to have sprung a microscopic leak. i.e. Just enough to cause the thermostat to short out if I close the unit up where the moisture can’t evaporate but not enough that the floor gets wet. So while it is necessary to replace it, I don’t have a great deal of pressure on me to do it right this minute.
So since I’m going to be plumbing I thought I’d consider some of the options, specifically a tankless or on-demand system.
I’ve talked to a few people who have had them over the years and hate them, but that is really too small a pool to base my decision on and there are far too many of them in use around the world for them to be completely a bad idea.
Any Doper types out there with direct experience? Would I have water hot enough to suit me? Will I notice it on my electric bill? The home is all electric btw.
Thanks!
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### Author:  [@Don\_t\_fight\_the\_hypothetical](https://boards.straightdope.com/u/Don_t_fight_the_hypothetical)
#### Post date: [March 18, 2008, 9:26pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/2 "2008-03-18T21:26:07Z")
I’ve recently installed [this](http://www.foreverhotwater.com/model-r98i-ASME.php) Rinnai. It runs the entire house. I like it.
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### Author:  [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)
#### Post date: [March 18, 2008, 9:50pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/3 "2008-03-18T21:50:58Z")
You mention electric - you might need to upgrade the wiring. Some tankless heaters need more amps than standing tank heaters. (Of course, this is more than made up for by not drawing any power when no water’s being used.) you should notice some drop in the electric bill, assuming you don’t use lots of hot water.
Anothe “gotcha” that seems to bug people - you will still need to wait for hot water to make its way to the faucet. A lot of people have equated “tankless” with “instant” but that’s not how it works unless you install a collection of small tankless units at the points of use, (eg: under the bathroom sink) rather than one house-sized one in the basement or garage.
As long as you get one sized to heat the maximum predicted flow rate for your home, you’ll have endless hot water. Want to take a 45-minute hot shower? No problem. The flow rate is the key though - if you’re taking a shower and someone starts up the dishwasher, will the heater be able to serve two uses at once? If not, your shower will cool off.
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### Author:  [@Chefguy](https://boards.straightdope.com/u/Chefguy)
#### Post date: [March 18, 2008, 10:02pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/4 "2008-03-18T22:02:43Z")
The only things we used overseas for eight years were gas-fired on-demand heaters. They were installed in each bathroom and in the kitchen, and were terrific. The only cautionary note is to make sure they are properly vented.
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### Author:  [@Patty\_O\_Furniture](https://boards.straightdope.com/u/Patty_O_Furniture)
#### Post date: [March 18, 2008, 10:51pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/5 "2008-03-18T22:51:30Z")
We talk about these frequently. Here are some recent threads I could find:
[Replacing hot water tank, considering tankless, opinions](http://boards.straightdope.com/sdmb/showthread.php?t=392777)
[plumbing question (tankless water heater)](http://boards.straightdope.com/sdmb/showthread.php?t=428239)
[Need some real numbers on replacing my Electric Water Heater with a Tankless system.](http://boards.straightdope.com/sdmb/showthread.php?t=455673)
[Do you have a tankless water heater?](http://boards.straightdope.com/sdmb/showthread.php?p=7143711)
[tankless water heaters](http://boards.straightdope.com/sdmb/showthread.php?t=451487)
The design is critical to get satisfaction from a tankless system. I’ll c&p what I said in one of those older threads:
[QUOTE=Patty O’Furniture]
Five units being served by one on demand heater? That might be the problem right there. I think the large majority of dissatisfied customers are the unfortunate victims of a poorly designed system. On-demand water heaters should, in my opinion, be sized only for one or two loads and placed as close as possible to the taps. If it takes 30 seconds to wash your hand but you have to wait 2 minutes for the hot water to reach the sink, that’s two and a half minutes of heating time of which you’re only using a fifth (if that - most people would probably give up waiting and wash under the cold water and shut the tap off just as the hot water arrives).
This is also the reason people get frustrated trying to adjust the temperature. It can take a little while for the temp change to get from the heater to the tap. Using a mixing valve rather than seperate hot and cold valves helps remedy this partially.
Also, since these heaters should feed only low-flow taps, it can take a little while to get the hot water from the heater to the tap. When I did my shower renovation I made sure the heater was as close as possible to the shower mixing valve. I’d estimate there is not more than six feet of pipe between the heater output and the shower head, and even at that close range it can take 15-20 seconds for the hot water to make its way to the shower head. The output of the water heater is hot instantly (I can feel the pipe get hot the instant the shower is turned on). It just takes time for the heated water to get to the shower head.
I’d also recommend using ½" cpvc to keep the volume of water in the pipe low, and to reduce heat loss that you’d get from a copper feed.
[/QUOTE]
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### Author:  [@Rick](https://boards.straightdope.com/u/Rick)
#### Post date: [March 19, 2008, 5:19am UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/6 "2008-03-19T05:19:03Z")
As I said in the last tankless [thread](http://boards.straightdope.com/sdmb/showthread.php?t=455673)
> [@Rick](#):
>
> Funny you should ask. I just finished changing out my 40 gallon water heater for a tank less unit. Since my water heater was nat gas, I went with natural gas.
> Issues:
>
> ```
> * A standard water heater has the water lines high, and the gas line low. The tank less unit has them all right next to each other, so you have to move the water lines down, and the gas line up. No big deal, you just have to tear into the wall and patch later.
> * Here is the biggie. The tank less unit requires a 3/4" gas line. The existing for my water heater was 1/2" This required some rather complex re-plumbing of the existing gas lines under the house to do the change over.
> * They don't make a flex line large enough for the 199,000 BTU input of my burner, so I had to hard plumb the gas line all the way to the unit.
> * You need an electrical outlet near the unit as it does require some (2A) of electricity to run the unit. I had to run a new outlet with a GFCI to near the unit.
> * The unit requires a 4" vent. the water heater required a 3" vent. I was very lucky that my house had a 4" vent installed in the celling so I did not have to change that out.
> * The unit was about $400 more expensive than a top of the line nat gas water heater.
> * Water is not quite as hot coming out of the taps. Regardless of how hot you set the t-stat there is a limit of how many degrees the unit can heat. It is more than adequate, but I can't get scalding water any longer.
>
> ```
>
> I have not yet gotten my first gas or water bill with the new unit, I expect my gas bill will drop by $20-30/ month, but I don’t know.
> I also expect a longer life out of the unit, but again I don’t know that for a fact.
> If you want to do this job yourself, I would classify it as for an advanced DIYer. This was not an easy job. I had a contractor help me. I am capable of doing it myself, but it was lots easier with a second set of hands.
> FWIW the guy at the plumbing store told me that this type of change outs start at $1000 for the installation. After completing it, I would bid it at more like $1500 if somebody wanted me to do it for them. It was a bitch.
I am still very happy with the unit, but it was a bitch to install.
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### Author:  [@Projammer](https://boards.straightdope.com/u/Projammer)
#### Post date: [March 19, 2008, 1:46pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/7 "2008-03-19T13:46:59Z")
**Patty** , I didn’t really want to start this thread because I was sure it had been done before.
How did you locate those threads with the search function disabled?
And thanks everyone!
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### Author:  [@Patty\_O\_Furniture](https://boards.straightdope.com/u/Patty_O_Furniture)
#### Post date: [March 19, 2008, 1:57pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/8 "2008-03-19T13:57:59Z")
Searched via [BoardReader](http://boardreader.com/t/General_Questions_33309/tankless_water_heaters_451487.html) for “straightdope tankless”.
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### Author:  [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)
#### Post date: [March 19, 2008, 3:12pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/9 "2008-03-19T15:12:06Z")
[QUOTE=Patty O’Furniture]
Searched via [BoardReader](http://boardreader.com/t/General_Questions_33309/tankless_water_heaters_451487.html) for “straightdope tankless”.
[/QUOTE]
I want to say how much I appreciate you going through the effort of collecting the threads, especially with the search function down. It’s normally a tankless job.
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### Author:  [@Mama\_Zappa](https://boards.straightdope.com/u/Mama_Zappa)
#### Post date: [March 19, 2008, 3:15pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/10 "2008-03-19T15:15:37Z")
I don’t see this in those other threads (will re-read; I just skimmed them) but it would seem that the best efficiency overall would be to have multiple smaller heaters, near each major user (kitchen, bathroom(s), clothes washer.
So I’d like to add this question, to the OP’s: Has anyone ever tried that approach and how complex might it be?
I’m assuming this would require electric vs. gas unless one wanted to put natural gas lines running all over the house! How large would such a unit be and would it typically require additional power over normal household circuitry? Would there need to be a unit in every room that required hot water or would one be able to have one “central” unit plus auxiliaries in a couple of rooms?
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### Author:  [@The\_Flying\_Dutchman](https://boards.straightdope.com/u/The_Flying_Dutchman)
#### Post date: [March 19, 2008, 3:41pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/11 "2008-03-19T15:41:23Z")
[QUOTE=Projammer]
The water heater in my home seems to have sprung a microscopic leak. i.e. Just enough to cause the thermostat to short out if I close the unit up where the moisture can’t evaporate but not enough that the floor gets wet. So while it is necessary to replace it, I don’t have a great deal of pressure on me to do it right this minute.
[/quote]
Such a “minute leak” suggests condensation or a plumbing connection problem so I hope you’ve considered that. Water heater failures are usually a little more dramatic.
> [@](#):
>
> I’ve talked to a few people who have had them over the years and hate them, but that is really too small a pool to base my decision on and there are far too many of them in use around the world for them to be completely a bad idea.
> Any Doper types out there with direct experience? Would I have water hot enough to suit me? Will I notice it on my electric bill? The home is all electric btw.
>
> Thanks!
I spent seveal months in a hotel in England back in 75 with an on demand water heater right in the bathroom, and the only problem I had was occasional scalding. I wonder if this new generation of tankless heaters have addressed the problem.
---
### Author:  [@masterofnone](https://boards.straightdope.com/u/masterofnone)
#### Post date: [March 19, 2008, 5:18pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/12 "2008-03-19T17:18:42Z")
[QUOTE=Mama Zappa]
I don’t see this in those other threads (will re-read; I just skimmed them) but it would seem that the best efficiency overall would be to have multiple smaller heaters, near each major user (kitchen, bathroom(s), clothes washer.
So I’d like to add this question, to the OP’s: Has anyone ever tried that approach and how complex might it be?
I’m assuming this would require electric vs. gas unless one wanted to put natural gas lines running all over the house! How large would such a unit be and would it typically require additional power over normal household circuitry? Would there need to be a unit in every room that required hot water or would one be able to have one “central” unit plus auxiliaries in a couple of rooms?
[/QUOTE]
I’m planning to do this once I build the actual house. Right now, I’m living in what will be the garage with a small appartment in it. I installed one LP Aquastar on-demand heater, and I love it, but I can see that in a larger house it would make more sense to have multiple heaters, to avoid a long lag time while you wait for the hot water to get to the fixtures. I would not put in one for every room that required hot water, but split the house into zones so that each fixture was no more than 20’ of pipe from a heater. It would require an extra gas line in my case, or electrical wiring if you went with electric, but it also means you only have to run cold water to each zone, so you have less plumbing to do.
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### Author:  [@Projammer](https://boards.straightdope.com/u/Projammer)
#### Post date: [March 19, 2008, 6:50pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/13 "2008-03-19T18:50:21Z")
[QUOTE=Patty O’Furniture]
Searched via BoardReader for “straightdope tankless”.
[/QUOTE]
I wasn’t aware of that resource. Consider ignorance fought this day. Thanks!
[QUOTE=Mama Zappa]
I don’t see this in those other threads (will re-read; I just skimmed them) but it would seem that the best efficiency overall would be to have multiple smaller heaters, near each major user (kitchen, bathroom(s), clothes washer.
So I’d like to add this question, to the OP’s: Has anyone ever tried that approach and how complex might it be?
I’m assuming this would require electric vs. gas unless one wanted to put natural gas lines running all over the house! How large would such a unit be and would it typically require additional power over normal household circuitry? Would there need to be a unit in every room that required hot water or would one be able to have one “central” unit plus auxiliaries in a couple of rooms?
[/QUOTE]
That’s a fairly common configuration, usually done with electrical heaters because of the issues with having to run gas everywhere and vent pipes for every unit. Though in some older homes the gas is already in place from where each room had it’s own heater. Many have been converted to central heat but the pipes are still in place. They would just have to be inspected and certified.
You are correct that larger wiring is needed, especially for single source installations. Not an issue for me though with pier and beam construction and a very short run to the breaker box. And being in the country the only inspection I have to pass is my own.
[QUOTE=The Flying Dutchman]
Such a “minute leak” suggests condensation or a plumbing connection problem so I hope you’ve considered that. Water heater failures are usually a little more dramatic.
[/QUOTE]
I have ruled out leaks at the water connections, still checking the heating element seal. The fact that the water is collecting behind the access door would strongly indicate that as the source, but no evidence yet. I will probably drain the tank and replace that gasket before I break out the big tools.
[QUOTE=The Flying Dutchman]
I spent seveal months in a hotel in England back in 75 with an on demand water heater right in the bathroom, and the only problem I had was occasional scalding. I wonder if this new generation of tankless heaters have addressed the problem.
[/QUOTE]
All the units I’ve researched had a control where you could adjust the absolute maximum temperature it they would put out. And I think they were all maxed around 130F.
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### Author:  [@NoCoolUserName](https://boards.straightdope.com/u/NoCoolUserName)
#### Post date: [March 19, 2008, 11:59pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/14 "2008-03-19T23:59:57Z")
Check your base water temp. Normal is around 50-55 F, but at our house it’s 42 flippin’ degrees. Since most tankless heaters raise the temp 50-60 degrees, you’ll want to make sizing adjustments based on the temperature the cold water is normally.
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### Author:  [@Rick](https://boards.straightdope.com/u/Rick)
#### Post date: [March 20, 2008, 2:35am UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/15 "2008-03-20T02:35:54Z")
[QUOTE=masterofnone]
I’m planning to do this once I build the actual house. Right now, I’m living in what will be the garage with a small appartment in it. I installed one LP Aquastar on-demand heater, and I love it, but I can see that in a larger house it would make more sense to have multiple heaters, to avoid a long lag time while you wait for the hot water to get to the fixtures. I would not put in one for every room that required hot water, but split the house into zones so that each fixture was no more than 20’ of pipe from a heater. It would require an extra gas line in my case, or electrical wiring if you went with electric, but it also means you only have to run cold water to each zone, so you have less plumbing to do.
[/QUOTE]
Don’t forget if you go with multiple heaters, there are a couple of extra issues.
If electric, you might have to up your service size to accommodate them. For example if you install three of [these](http://www.cpotanklesswaterheaters.com/electric_products/whole_house_tankless/ae125_spec.html) there is no way in hell you can get away with it on a 200A service. You will probably have to go to at least a 400 A service. (somebody much smarter in the in and outs of AC electrical service will come along shortly to straighten me out on this I am sure)
If you are installing gas units, you have to have a place to put them, and fresh air to them, as well as venting for the exhaust. You also have to have an electrical outlet to power the unit.
IOW TANSTAAFL
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### Author:  [@masterofnone](https://boards.straightdope.com/u/masterofnone)
#### Post date: [March 20, 2008, 2:18pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/16 "2008-03-20T14:18:47Z")
[QUOTE=Rick]
Don’t forget if you go with multiple heaters, there are a couple of extra issues.
If electric, you might have to up your service size to accommodate them. For example if you install three of [these](http://www.cpotanklesswaterheaters.com/electric_products/whole_house_tankless/ae125_spec.html) there is no way in hell you can get away with it on a 200A service. You will probably have to go to at least a 400 A service. (somebody much smarter in the in and outs of AC electrical service will come along shortly to straighten me out on this I am sure)
If you are installing gas units, you have to have a place to put them, and fresh air to them, as well as venting for the exhaust. You also have to have an electrical outlet to power the unit.
IOW TANSTAAFL
[/QUOTE]
Thanks **Rick** , but mine are LP and I specifically bought them to require no electricity, as I’m on a mountain and usually I am without power for about 2 weeks over the course of the average winter. You bring up a good point re. fresh air though. I initially wanted to put mine in the bathroom, but manufacturer’s specs specify that it should not be put in a small room with a door that can be closed without having huge vents in the door.
PS - what’s TANSTAAFL?
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### Author:  [@beowulff](https://boards.straightdope.com/u/beowulff)
#### Post date: [March 20, 2008, 2:37pm UTC](https://boards.straightdope.com/t/tell-me-about-tankless-water-heaters/441835/17 "2008-03-20T14:37:16Z")
[QUOTE=masterofnone]
PS - what’s TANSTAAFL?
[/QUOTE]
There Ain’t No Such Thing As A Free Lunch, popularized by Robert Heinlein.