# What can you tell me about on-demand gas water heaters?



## jmr106 (Nov 30, 2016)

I've got a 40 gallon natural gas water heater hanging out in a swimming pool hole, basically. The original thought was to elevate it. Then I thought about an external on-demand on the back of the house. That's a complete failure after learning just how hard those are to keep maintained constantly and how often you'll go through water heaters (from what many others have told me) if you don't constantly maintain it. Then there's the cold, worrying about insulating the pipes and all of that.

The crawlspace stays fairly warm because the furnace is there and it outputs some heat from the top of the pipe on the condensation pump. So if it is set for 70 in the house, it might be 60+ in the crawlspace even when it is 40 outside. So, I'm pondering an on-demand natural gas water heater. 

How reliable are they? How much regular maintenance do they require vs a regular natural gas water heater? Will the gas bill shoot up and double/triple by getting one? Small 2 bedroom, 1 bath house. No dishwasher is used (we prefer the old fashioned way, anyway) and we don't do a bunch of chaining of showers back to back. We don't use a ton of hot water.  What all would be required? More efficient than regular gas water heaters?

It could be installed just feet from the stack vent that goes up through the roof. Will a larger gas pipe be needed? Is there a way to determine if my current gas meter has a high enough flow rate for such a thing without changing the pipe and/or meter?


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## nealtw (Nov 30, 2016)

http://www.tanklesswaterheaters.com/tanklessfaq.html#14


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## jmr106 (Dec 3, 2016)

If I get an on-demand natural gas tankless...here's an odd question:

Can it be mounted on one of the floor supports for the house? There are many of these down there about 4-6 feet apart going across the middle of the house. They sit on top of the crawlspace dirt, which is basically so hard that it is like a rock. One of these supports sits about 4-6 feet away from the roof vent that the current water heater connects to. Obviously, the water and gas pipes need to be relocated and redone, which is expect. 

It may be a little odd, I'm not sure. There aren't a lot of places down there to attach such a thing. I would expect that in most crawlspaces, there likewise wouldn't be anything to attach it to. I could build a wall for it somewhere next to the vent, but I figured...these are already down there.


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## Snoonyb (Dec 4, 2016)

There are particular conditions that make an enclosure common sense.

Insulating any hotwater heating appliance piping that is not within the conditioned envelope, would be a prerequisite, from just an efficiency standpoint, and a crawl space is not considered within the conditioned envelope.

You should check with your local building authority regarding the placement, because codes change and you may be required to install an alarm or even fire suppression systems.

Look at all the heater mfg. while the information is "generally" the same, do the research, know the game.


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## jmr106 (Dec 4, 2016)

Insulating it would be the easy part. The question I'll be asking the potential installer (will get a quote first since there's so many factors) is where it can be mounted safely. I've asked various people and one of them stated that I could try to mount  it to the floor joists. I would think that would be even worse as far as safety, likely not even possible to due the size and I'm pretty sure they only work vertically. This seems to be the best solution to get it out of the hole completely. The company that I have in mind does HVAC, water heaters, gas and electrical...so they can kind of look at the odd setup down there and tell me what would be best regarding the furnace in the same said hole, as well. First thing will likely be the water heater, however. It is most subject to flooding in a power failure.

But in the meantime: is it going to be feasible at all to mount to those foundation blocks, or not really? Would it theoretically cause and damage or affect their stability? It will probably be a 6GPM to 8GPM or something like that. We don't use a crazy amount of hot water. The average size seems to be approximately 2+ feet tall, about 15 inches or so wide and about 8" to 12" thick.


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## Snoonyb (Dec 4, 2016)

The individuals who are doing the installation, "may", know the code, or may not care.

If those who have offered an opinion are not a member of your local building authority, it's a guess, and I'll bet none would be your home insurance agent.


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## buffalo (Dec 4, 2016)

Not sure about any codes in your area ,  buT if mounting to block I'd tap con 2 pressure treated 2x4 to the block . Then mount a 3/4 " peice of plywood to that , then mount heater to that . You could do a similar thing to the joists . I've only seen direct vent ones , not gonna use the chimney , pvc out the sidewall .


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## joecaption (Dec 4, 2016)

What do you mean by a swimming pool hole?
What's your location?
Got a picture?
Just can not imagine installing it in a crawl space like that.
Lots of moisture that's going to effect the electronics, good luck trying to get a plumber crawl under there to try and fix it.
It still needs to be vented.
No way is there going to be a cost effective pay back time after the cost to install, the added maintaince.


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## jmr106 (Dec 4, 2016)

joecaption said:


> What do you mean by a swimming pool hole?
> What's your location?
> Got a picture?
> Just can not imagine installing it in a crawl space like that.
> ...



Location is about 15 minutes east of Atlanta, Georgia.

There's more pics than you ever want to see here. http://www.houserepairtalk.com/showthread.php?t=19909  First page has the general description of the problem.

This has generated so many threads on here that I've lost count. Its HVAC, general plumbing/water heater stuff, then general crawlspace issues and water issues all wrapped into one. 

But if you look in the last page of this thread (http://www.houserepairtalk.com/showthread.php?t=21770&page=3), the water seems to have "stopped" randomly after I found and filled an old septic tank just outside of the back of the house. I'm unsure if the water table shifted temporarily or what. We had nearly 3 inches of rain the other day and yesterday, and today, we've had another two inches or so. We're supposed to get about another inch tomorrow and Tuesday. I haven't seen any more water flowing in there, so I'm confused. What I do see is lots of white mold/mildew...I found a "blanket" of white mold forming where water used to go, behind the furnace system on the floor of said hole. It is growing on the dry dirt from apparently previous moisture. Even on dry days, I see a little moisture barely seeping through to make wet spots on the inside of the wall. Not sure if that's just ground moisture, very minor springs or what. So regardless, I have to get that hole taken care of somehow. That same problem with the furnace system in the same hole: the company that put it in are idiots. When they sent some more people out to consider flipping it, they told me, "Why didn't they put it in that way to begin with?" as if shocked by the stupidity of their coworkers. 

I'm not sure what to do with this situation. I've saved up a considerable amount of money specifically to fix the issues and get the furnace and water heater out of the hole, but even then I don't know what to do with the stupid hole. An external water heater would freeze on the back of the house and apparently those have constant issues with needing maintenance. I've had tons of people tell me to stay far away from external tankless water heaters outside of the house. Inside of the crawlspace...the moisture there is an issue. Concern of corroding the electronics and such. I could replace it with a similar tanked water heater (which is what is there now) and elevate it on a stand that I could build, but that just elevates it in the hole. There has been talk of flipping the system, adding about 30 inches or so of gravel in the hole and putting in a proper sump basin in the gravel. Some people think that's a good idea, others don't feel that it is. So yeah...its a headache, for sure.


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## kok328 (Dec 5, 2016)

This is a gas fired appliance and certain clearances must be maintained for fire code reasons.
So I would not think that attaching it the floor joists or mounting it on treated lumber would be an option.
Tapcon some unistrut to the blocks and mount the unit to the unistrut should suffice and keep you out of trouble with combustibles.
Narrow down your choice of heaters and see if you can google the manufacturers installations instructions and see what they all have in common and what some have as unique options.
Educate yourself so you can sort out bull from fact before talking to contractors,


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