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Discussion Starter · #1 · (Edited)
Hello Everyone,
Does anyone have a natural gas tankless (whole house) water heater recommendations or input? I'd like to disconnect our gas hot water heater and install a tankless unit instead. I"d then eventually use the hot water heater as a pre-heater.

Our home is 3k square ft with 2 1/2 baths. We use quite a bit of hot water in a given day between two adults and two children. It probably fluctuates between 30 - 50 ga though. The main daily consumption is filling a garden tub at least once and running a load of clothes in the washing machine in addition to maybe one short shower. The dishwasher typically gets run every other day and several other short showers, so that would account for the high consumption days.

1. We typically are not running multiple items at the same time so the demand is never really outrageous at any given moment.

2. Does the vent system have to be changed out from a standard gas water heater to a tankless gas water heater? The unit will be located in our garage, btw.

3. How much savings could I expect?

I appreciate your input.

God Bless,
Ralph
 

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I'm betting you'll need one tankless unit per hot tap. One day of running low or out of hot water and you'll regret the change over.
 

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Take a look at the Takagi tankless heaters. They have sizing charts on their website but you will probably need a 199,000btu unit.
Sometimes you can reuse existing vent lines but if you go with a condensing (more efficient) tankless then you will switch over to either 3" or 4" PVC.


Make sure you have a 3/4" gas line serving the heater as in most cases 1/2" is too small.


Good luck. You will probably get more responses if you post in the "Plumbing Section" rather than appliances.
 

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Discussion Starter · #4 ·
I'm betting you'll need one tankless unit per hot tap. One day of running low or out of hot water and you'll regret the change over.

I only need it to be able to fill a bathtub or otherwise run a shower. The bath or shower will not be occurring at the same time. Nor will the bath or shower occur when other appliances are running (dishwasher, washing machine). So how do you figure it will run out of hot water?


Ralph
 

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What problem are you trying to solve?

Tankless units are expensive to buy and service. They have proprietary parts and are very complex. They don't have a reserve - think about power outages and breakdowns.

They save fuel but not normally enough to justify the high costs.
 

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Think long and hard before you go tankless.

Google "hot water sandwich" before you commit.

The amount of water you and your family send down the drain because you are afraid of the cold water sandwich will more than offset the savings that your plumbing salesman guaranteed you will be saving.

It is amazing the plumbing industry is still selling these things.

You have been forewarned.......
 

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I installed a Takagi 10 gallon per minute natural gas unit about 3 years ago. It easily handles several points of use at the same time, although the temp can fluctuate a little when you drastically change flow through the unit. It takes a few seconds for the temp to readjust and match the new flow rate. If I turn on both showers, and all four sinks, it can easily supply all of them simultaneously. All the hot taps in my house together can reach about 8 gallon per minute. This unit will maintain 120F even with incoming water temps likely dipping into the 40s in winter.

It does take longer to get hot water, probably about 15-20 seconds at the nearest sink and 30 seconds in the kitchen as it's the furthest away. If someone uses a bunch of hot water while you're in the shower the temp changes a little, it's mildly annoying but not a huge temp swing. Cold water sandwich has never really been a big issue, you just get used to running the shower a minute before you jump in. Tankless isn't a great option if you have hard water, it will require much more maintenance.

The tankless is really nice for filling large tubs or those times when several showers have to be taken in a row. I can set the temp at 105 and fill my 500 gallon hot tub and it's ready to go immediately rather than the next day. My gas bill dropped about $5-7/month after install. It's the only gas appliance running for half the year so it's easy to see. Didn't notice significant increase in water usage although I imagine we do waste a little more water waiting for it to get hot.

I went with tankless because of previous experience. I had helped a friend install two of them in his car wash a few years earlier. He'd been buying 100 gallon high capacity commercial units about every 3 years at about $5000 a pop. We installed the two tankless units for about half of that and they've been in use since around 2011 with pretty much no issue. When my power vent unit failed it was $750 not including install. I have no flue pipe through the roof so a standard tank type is not an option. This is a condensing tankless unit, so it uses two 3" PVC pipes directly out through the wall, one for intake and one for exhaust.
 

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Discussion Starter · #9 · (Edited)
Hello Everyone,
Thanks for all the input and let me clarify a few things.

1. I am not fixing any issues associated with our 50ga gas water heater. I simply want to make our house a little more efficient in order to lower our utility bills.


I've done construction and remodeling most of my life so I'm assuming I can do the install myself? After taking the 50ga hot water heater off line my plans were to then use it as a pre-heater for the tankless at some point. So instead of it having to warm up 59 degree water it would only have to warm up 80 degree water or so....

2. I do not see Hot Water Sandwich being an issue at all. We always check the tub temperature and adjust as needed while it is filling. In addition, it takes about 25 seconds for hot water to reach the shower so nobody ever gets into the shower prior to that.

3. I'd have to check the water quality but iron isn't an issue whereas hard water could be a concern. We definetly do not have soft water.

We just need something that could supply enough flow for one shower. Really if it takes 15 or 20 min to fill the tub that is no big deal but it must support a shower. Consequently, I was assuming a tankless 4.0 gpm or 5.0 gpm would be sufficient.

Our demand is spread out over the day or most of the evening. We never have a high demand all at once.

God Bless,
Ralph
 

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Hello Everyone,
Thanks for all the input and let me clarify a few things.

1. I am not fixing any issues associated with our 50ga gas water heater. I simply want to make our house a little more efficient in order to lower our utility bills.


I've done construction and remodeling most of my life so I'm assuming I can do the install myself? After taking the 50ga hot water heater off line my plans were to then use it as a pre-heater for the tankless at some point. So instead of it having to warm up 59 degree water it would only have to warm up 80 degree water or so....

2. I do not see Hot Water Sandwich being an issue at all. We always check the tub temperature and adjust as needed while it is filling. In addition, it takes about 25 seconds for hot water to reach the shower so nobody ever gets into the shower prior to that.

3. I'd have to check the water quality but iron isn't an issue whereas hard water could be a concern. We definetly do not have soft water.

We just need something that could supply enough flow for one shower. Really if it takes 15 or 20 min to fill the tub that is no big deal but it must support a shower. Consequently, I was assuming a tankless 4.0 gpm or 5.0 gpm would be sufficient.

Our demand is spread out over the day or most of the evening. We never have a high demand all at once.

God Bless,
Ralph



I have my old 30 gallon electric water heater set up in line ahead of the tankless and my ground source heat pump desuperheater is used to heat the water in it. I don't often run it through the winter because I do lose a little heating capacity when the desuperheater is operating. I do run it all summer when the AC is on and it does preheat the water although not really enough to supply hot water on it's own except during stretches of extremely hot weather.

If I didn't have geothermal to make free hot water, I wouldn't even bother. The tankless works more evenly without the preheated water and it doesn't need any help. I do have the old electric water heater connected to power. If the tankless were to go out I could just flip the breaker on and have hot water in an hour or so.

The link I included is for the 10 gallon model, you can also get 8 or even 6gallon, but the savings was not enough to sell me less capacity. Looks like less than $50 savings for the 8 gallon and about $175 savings for the 6 gallon. When I bought mine they were even closer in price.

To do this to strictly reduce your utilities, I think tankless would have a pretty long payback. The space savings is pretty significant, having it hung on the wall freed up a lot of space in a congested area. The endless hot water is the biggest benefit. I actually needed a new water heater so it only cost me about $300 more to go tankless.

It can be DIY, I installed mine. I use electric for heat but the house already had a 1" main line. The only other gas appliance on the place is a small furnace for the garage. If you were to have several gas consuming appliances you may need to upgrade the main gas line to larger size and in extreme cases maybe even the meter. Another option may be to have the utility company switch you to higher pressure gas service and regulate pressure at each appliance.

I carefully read the manual and installed the vent and intake according to the directions. Installing this is really no more complex than installing a tank style heater. I had to make changes to my gas line, separating a couple joints and installing a larger Tee for the water heater. I have years of experience fitting pipe at work, so this little gas line project was no issue for me. After completion I pressure tested the line and checked each connection with soapy water. Also you'll need a good manometer to verify correct gas pressures during the full range of heater operation.
 

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So how do you figure it will run out of hot water?
You'll run out of hot water when your gas supply is depleted. Otherwise it will keep heating until you are through. We don't have the demand you have, but are very satisfied with our Rinnai unit. Venting is 4" PVC, as opposed to the early version of tankless which required quite expensive triple wall pipe.
 

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Discussion Starter · #12 ·
Thanks!


Let me ask one other question.


Would it be cost effective to install a 120v or 240v tankless at the shower alone? There is a large cavity behind the shower everyone uses that could be made accessible from a closet. The tankless unit wouldn't be easily accessible though (not sure about code) but it could be accessible once a year of ever so often to check on it. Running single pole 120v would be easy as I have a line available already. I'd have to run new wire for 240v over 40ft so that would cost a little more.


Ralph
 

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That sounds like a good idea to me and I have thought about doing it for my master bathroom that is the most distant from my regular nat gas tank WH. But in my case I don't have a lot of extra room for one or an easy way to plumb it... and no way to get 240V service up there through 3 floors of finished space and walls... so I just live with what I've got.... which means I need to run the hot tap on the tub for 20 seconds or so to get hot water to my bathroom for a shower... or run the shower for like 45-60 seconds. And forget about just running a hot sink tap and getting hot water today. <sigh>

I also looked hard into tankless when I replaced my tank WH awhile ago but the retrofit costs were just way too high, having to run intake and exhaust pipes, upgrading the gas lines... and maybe even the gas service and meter. Made no sense at all. It would be much easier and make more sense in new construction as long as the water hardness and maintenance issues are understood.

Thanks!


Let me ask one other question.


Would it be cost effective to install a 120v or 240v tankless at the shower alone? There is a large cavity behind the shower everyone uses that could be made accessible from a closet. The tankless unit wouldn't be easily accessible though (not sure about code) but it could be accessible once a year of ever so often to check on it. Running single pole 120v would be easy as I have a line available already. I'd have to run new wire for 240v over 40ft so that would cost a little more.


Ralph
 

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Thanks!

Let me ask one other question.

Would it be cost effective to install a 120v or 240v tankless at the shower alone? There is a large cavity behind the shower everyone uses that could be made accessible from a closet. The tankless unit wouldn't be easily accessible though (not sure about code) but it could be accessible once a year of ever so often to check on it. Running single pole 120v would be easy as I have a line available already. I'd have to run new wire for 240v over 40ft so that would cost a little more.

Ralph

Even a small electric tankless takes a lot of power. The smallest I've seen would still require a 30 amp 120v circuit. Friend has one of these in his garage, it can barely warm the water to wash your hands and it takes a good 30 seconds to even do that. Good for less than half gallon per minute flow, as long as the incoming water doesn't get too cold. In winter the water from the faucet can barely be considered warm.

A unit large enough to handle a single shower would probably require around 50 amp at 240v which would likely require #6 cable at about $2 a foot. A whole house electric tankless can easily take 3-4 times that. In most houses it would also require a major upgrade to the electric service to handle it.
 

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Discussion Starter · #16 · (Edited)
How would you flush it? Don't forget proper maintenance.
The unit could be mounted on a wall within the bathroom. I would then create an access door within the master closet to the attic cavity (located behind shower) that would allow me to service the unit from the backside. So there should be no issue there.

It's just not readily accessible because I'd have to move clothes and such in order to access it.

Take care,
Ralph
 

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In 2000, I built my dream house and installed a Bosch Aquastar 125B tankless. Other than changing the ignitor batteries (2 D-cells) every couple of years, it was NEVER touched. Never serviced, never flushed, never nothing. It just quit a couple of months ago. The upfront cost ($900) installed was more, but... Did I ever run out of hot water? No. Did I ever pay a service bill? No. Did I save $$ over the approximately 2.5 tank heaters I would have used over the same time period. Yes. Did I save on NG? Yes. On the recommendation of a plumber I trust without question, I had him put in a Navien 180S. This time the cost was $1950 total. It can fill the whirlpool in the master bath and run a shower full blast at the same time. (I haven't tried running 3 fixtures at once. I question the experience of those telling you that you'll need "one tankless per tap," or "they are expensive to maintain and repair." That hasn't been my or my neighbor's experience (they put in a Rinnai 10 years ago). Just endless hot water and no service or repair bills. I'm a tankless fan for life.
 

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When hot water needs are low (2 to 3 people showering), even if a tankless saves 40% it doesn't make economic sense to go tankless.

There may be other good reasons to get this type of water heater.

Some units may run trouble free for many years, others may require very expensive repairs.

A tankless unit is basically a modulating wall mount boiler -> the gas valve and inducer are variable capacity, it must constantly monitor leaving water temperature and adjust fuel input to deliver the correct temperature water. The electronics needed to make this happen are proprietary.

I haven't looked into repair part costs but wouldn't be surprised if the circuit boards on some are $500 to $1000 at cost and need to be ordered.

A conventional tank water heater on the other hand can be fixed with mostly inexpensive parts commonly stocked on a service van.
 

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Hello Everyone,
Thanks for all the input and let me clarify a few things.

1. I am not fixing any issues associated with our 50ga gas water heater. I simply want to make our house a little more efficient in order to lower our utility bills.

God Bless,
Ralph
You sound like a frustrated engineer! (Tongue in cheek)
You want to take something that is working fine, and then replace it for no good reason. You will double or triple the complexity, cost, and maintenance of your system in the hopes of saving a tiny amount of money that will require a 30-year payback. All the while introducing new issues that you could not foresee.

Reminds me of a friend with a very suitable economy car. He replaced it with a Chevy Volt because it would make his daily round trip commute more efficient. Shortly after, Ohio introduced a $300 annual tax on plug-in hybrids, to recover lost road taxes from people with electrics who don't pay their fair share of gasoline tax.) Now my friend spends more on this annual tax each year than he saves in gas.
 

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An additional two cents. I have traveled extensively in Europe and Asia. In those parts of the world, you will almost never see a tank water heater. Tankless water heaters are the standard in home, commercial and industrial applications going back to the 1940s. (Of course, what would most of the rest of the world know about anything, right? 'Murica!)
 
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