Tank or Tankless

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Old 04-18-09, 07:03 AM
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Tank or Tankless

Have to replace a hot water tank. Have two that run tandum. Will I be able to just replace the one tank with a tankless and leave the other tank until it needs to be replace, or will have to replace both to a tankless system? From the calucation from several site that have tankless system will have to use a tandum system to beable to supply peak hot water flow for the house. Thank you!
 
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Old 04-18-09, 07:19 AM
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Don't know what your requirements are, but the Takagi TM-1 gas fired unit at my house will supply two showers and a washer or dishwasher at the same time even at Chicago's low winter water input temps.

..................

I don't sell, install or service water heaters, but I have gas fired tankless water heaters at my home, my office and at 3 of our rentals. They can work well, but we encountered a number of issues when installing them, mostly related to installers' limited familiarity with tankless heaters' special requirements. Iíve put up this page describing some of the installation issues we encountered, and how to resolve them:

Tankless Water Heater Installation FAQ - Paragon Home Inspections Evanston / Chicago / Skokie / Wilmette / Morton Grove / Glenview / Northbrook / Illinois
 
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Old 04-18-09, 08:16 AM
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ok, first have a read here Welcome to Tankless101.com

Mr. Thomas's post was not bad and basically says pretty much what the site i posted says to a point.

one thing i definately agree 100% with from the previous post is that the installer needs to know what they are doing and should be a manufacturer authorized installer. many people have installed their own tankless and some have actually gotten lucky and are happy with the tankless while others hate them because of improper sizing or installation and they dont even know those are the reasons they are unhappy

installing one tankless now is not a problem as the better brands (rinnia, takagi and noritz) i know for sure can be installed in a number of configurations incorporating tank heaters.
 
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Old 04-18-09, 05:09 PM
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I was listening to the gas guys this past week as I was doing other work on a house and they were supplying the stove with a new gas line. The customer was questioning them about where to put a tankless WH. I was flabbergasted to hear the cost of 2' sections of exhaust pipe ($60 each)! So I guess the closer to an outside wall, the better, huh?
 
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Old 04-18-09, 05:50 PM
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that takagi can go outside I think.
 
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Old 04-19-09, 05:34 AM
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rRsnyder has not filled out his/her profile, so we don't know where then unit will be installed, but tankless units can only be installed at the exterior in climates where thy are not subject to freezing - in climates like mine (Chicago) even when installed at the interior they may require back-draft dampers and auxiliary electric heating elements to prevent freeze-ups.
 
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Old 04-19-09, 05:52 AM
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Originally Posted by chandler View Post
I was flabbergasted to hear the cost of 2' sections of exhaust pipe ($60 each)! So I guess the closer to an outside wall, the better, huh?
Yup, that stuff is very expensive. One alternative are the condensing units that can be vented through PVC.
 
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Old 04-20-09, 07:44 AM
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Michael Thomas, mentions his unit, a TM1 which is an older model light commercial Takagi. Nice unit, but so many people many times over calculate their flow requirements, and select a heater more than needed. The TM1 for instance requires .75 GPM to initiate the combustion/water heating process that can be a real pain when trying to draw hot water at a responsible or smaller flow rates such as a lav faucet that is .5GPM. You see without removing the aerator and running at full stream, he will never get hot water with most modern day faucets.

So calculate your demand requirements, not what you have such as two tanks that were applied because of potential heavy draws or large tub filling requirements and select the appropriate tankless(s'). Knowing incoming water temp, home water requirements, and max temp needed (temp rise) is how it is done. Take for example, 2.5 bath home. On occasion, both showers may be running, so thats 5GPM, at 2.5 each, using 120F water mixed to about 105-110 max. Using Takagi as an example, the TK3 will do about 5.5 GPM at a 60F rise. So mixing in cold you would have potentially 6.5 GPM available for bathing thus, supporting two simultaneous showers with a bit to spare.

Commenting on replacing two tanks, remember on-demand tankless delivers endless hot water with the GPM dictated by BTU's of unit, incoming water temp, desired output temp and piping, valves and system pressure and delivery.

Based on above something to consider, if you once had a 2-50 gal tank set up and it took 9 minutes to fill your whirlpool, it may take 12 minutes to fill it from one tankless heater but, there is no recovery time to a tankless so the whole house still has hot water when done filling the tub. With this adjustment in lifestyle, there is no reason to oversize the unit or install two in many cases.

One last thing, unlike the cheapo tankless available at so many hardware stores, quality tankless regulate the flow of the output to control near perfect output set temps. so when the flow requirement of the house exceeds the BTU/ water heating capability, it throttles back the flow leaving the heater. So what does that mean? say you have 3 showers running at once and the mixed temp capabilities is 6.5 GPM, everyone splits the output water thus, they all by theory get a 2.1 GPM shower till the first of three, shut theirs off. Is that such a big deal? in my opinion, not a reason to overbuy or install a second unit.

Tankless don't belong outdoors with exception to southern Texas and Florida, and still I dont like it with all the critters.
 
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Old 04-20-09, 09:21 AM
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i dont know about your calculations but an under sized system is worse than an oversized one, but that is what proper sizing using calculations prevents.

i want to be able to fill the tub and do the laundry at the same time and maybe run the dishwasher also
 
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Old 04-20-09, 10:24 AM
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To reiterated what I posted, a quality unit will do that, run all fixtures but on occasion should you exceed the total flow potential of all fixtures flowing water, it divides the pressure/flow up. Much the same as a water service with demand exceeding supply, all outlets get less pressure and volume.

I don't totally agree with the over-sized system (unit) is better than a undersized, case in point someone that wants to meet higher flow rate requirements and chooses a commercial unit will quickly discover that .75-1 GPM is required to activate burner thus most lav and kitchen faucets wont work. There is of course the option of properly installing two units and if properly cascaded and controlled will work quite well. But again if it is just for a occasional use tub is the deciding factor for adding the second unit or guests in the house once a year, does it make sense? Will it really matter if the tub takes 3 more minutes to fill to save to cost of a second heater install?

Those are just some of the differences tankless users must understand and adjust to. North America being the only consumer of gas fired hot water tanks, we are the last to understand both the benefits but also some of the handicaps of all tankless units. We are a wasteful nation, just look at the cars we buy.

It never ceases to amaze me the misinformed public that removes their 60 gallon electric tank heater and replace it with a 25KW tankless electric heater and then complain that it doesn't work. Some people just don't do their homework or just not able to understand BTU's temp rise and flow rates of units and fixtures.


Most often when you hear or read about disappointed tankless users, there is one common thread. They have a cheap Home Depot unit that delivers fluctuating water temps, inadequate hot water because of low BTU's or an undersized electric unit that cant provide adequate flow rates without buying one that may consume 3/4's of their electric service.

For the record, I have a Takagi TK3 (199M) in my 4 bedroom, 3.5 bath home with multiple heads in MB, jacuzzi tub, and all the amenities served by a 1" water main with zero water supply issues. Yes I fill the tub and shower and on occasion do laundry or dishes all at once.
 

Last edited by ZL700; 04-20-09 at 10:49 AM.
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Old 04-20-09, 02:08 PM
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but dont forget that sizing it for your needs instead of the fixture load is not the way to go since one day someone else is going to own/live in that house and may have need of a bath that wasnt figured in the sizing and now they are ticked because it wont deliver what they need.

i see that all to often, customers saying oh well i dont use this and that so the smaller one will do for me
 
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Old 04-20-09, 06:41 PM
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Another thing I often seeing people forgeting about is pressure loss. When determining the size also make sure the pressure loss is reasonable for that gpm. For example, the TM1 has a pressure loss of ~10 psi at 5 gpm. In some cases this is no problem, but 10 psi on a borderline system can cause alot problems. This can also affect pressure balanced fixtures.
 
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Old 04-21-09, 04:55 AM
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Five years ago, when I installed my TM-1, there were few options for higher output units for residential use, today their lot more choices. (BTW, irrespective of the stated .75 gal/min minimum flow rate, the unit is operating successfully with low-flow shower heads and standard modern faucets with the aerators in place).

There a number of factors which come into play when designing demand hot water systems compared to tank type systems.

For example in my location (Chicago) I have measured input temperatures the unit as low as 38-39įF - as the flow rate on a tankless unit is a factor of the desired output temperature and the input temperature, a system designed to a given demand in my climate is going to require a much higher output unit than one installed in Los Angeles - these are definitely not "one-size-fits-all" units:



Similarly, in my area were most residential structures are 1 or 2 stories in height and on municipal water systems, pressure drops are typically not a significant concern, in other areas they can be an important concern.

Also IMO you really do have to design for peak reasonable demand, for example my wife and I are up at the same time every morning and taking simultaneous showers, at the same time the dishwasher or clothes washer may be running - this is not a matter of a thoughtless lifestyle in terms of energy consumption, this is a direct result of our very heavy work schedules, very long work days, very limited time available for household tasks, and my having come to a very clear understanding as a result of my job (home inspection) that you should never, ever, leave an appliance with the potential for a major water leak running unattended.
 

Last edited by Michael Thomas; 04-21-09 at 06:06 AM.
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Old 04-21-09, 05:33 AM
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i agree 100% but as for the not running unattended that is what they have all them purdy water alarms and shutoff systems for now-a-days
 
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Old 04-21-09, 05:49 AM
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Originally Posted by plumbermandan View Post
i agree 100% but as for the not running unattended that is what they have all them purdy water alarms and shutoff systems for now-a-days
FWIW I have auto-shutoff valves on the dishwashers, washers, and ice makers in all of my rental units. The one time I had a leak, the valve failed - my autopsy of that valve in one reason it was extensively redesigned by the manufacture.
 
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Old 05-08-09, 07:30 AM
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Others may have been aware of this, but it was news to me, the tax credit on qua

Others may have been aware of this, but it was news to me, the tax credit on qualifying tankless units is now 30% of cost, up to $1,500. (For the record, I don't sell, install or service any type of water heater).

Federal Tax Credits for Energy Efficiency
 
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Old 05-08-09, 10:22 AM
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so if it costs $5k to install you will get a tax "credit" not "deduction" which means you get $1500 off your tax bill or back if you owe nothing
 
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