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Old 07-17-2015, 03:35 PM   #21
Bus Geek
 
Join Date: Aug 2011
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The only time a "Tankless Water Heater" should be considered is if space savings are deemed worth the trouble to follow.

Con's Of Tankless Water Heaters.


Mineral in water.
Unless you filter the water entering your tankless, it will foul and in time plug off the heat exchanger. A small fouling can lead to water not heating hot enough, low flow rates, and eventually failure. Flushing and cleaning the heat exchanger once or twice a year is needed to prevent this.

Parts
.
All tankless heaters use parts specific to that unit. Also parts are only available from that manufacture. Many cheaper units parts are simply not available.

Complicated.
Do you really want a computer in your water heater? Do you want to have to go to school just to fix a hot water heater? I don't.

Modulating burner.
Most tankless water heaters use a multi head burner to heat the water. This allows only the amount of heat needed to heat the flow of water.
Now if you mostly only wash your hands in the sink for a few months, then go to jump in the shower, the burners may be fouled from lack of use, and not fire, resulting in cold water.

Cold water sandwich.
The tankless water heater may not like the low flow of the shower or hand sink, causing the heater to cycle on and off causing hot, cold, hot, ect.
To remedy this, many plumbers install a 5 gallon tank to mix the hot and cold water. This completely defeats the purpose of the tankless heater.

Massive energy draw.
Propane heaters this may not matter, but in the case of electric, you would need the full 50 amps just to heat water. Most folks don't have 50 amps unless connected to shore power. Even then, that kind of massive electricity pull is not healthy of the entire camp ground power grid.

Cost.
Most tankless heaters cost 2x to 4x what a tank heater would cost.


Now for the pro's of the tank water heaters.



Mineral in water.
Gas fired Tank water heaters have more surface area where the heat exchanges. This prevents the mineral buildup from causing heating issues.

Electric tank heaters only develop mineral deposits on the heating elements. This builds up and flakes off, falling to the bottom of the tank where it will cause no harm. Mineral buildup on the elements can also be detected by listening to your heating tank. The buildup will cause micro boiling that sounds like the tank "hissing" or "singing".


Parts
.

99% of gas fired Tank water heaters use standard parts that can be purchased almost anywhere from big box stores to hardware stores.
Same for electric tank heaters. Parts are cheap. A new thermocouple for a gas unit is around $25, and a electric heating element is around $20.

Complicated.
Tank units are simple, and most use standard off the shelf parts. Any DIY person can repair and service a tank water heater.

Modulating burner.
No such thing in a tank water heater, therefore this is not a issue.

Cold water sandwich.
Tanked water heaters only allow hot water to exit the hot port until the hot water is depleted.

Massive energy draw.
Electric tank heaters can be fully customized for low cost. The electric heating elements can be sized from 12 volts DC 40 watt, all the way to 240 volt AC 4500 watt and beyond.

Small tanks with a single element can be had for around $200.
Larger 2 element tanks can be had for only $250 and up.

Tanks with 2 elements can be customized to use both elements at the same time, or 1 at a time. Elements can be sized to allow use of low voltage / amp electrical connections, or high voltage / amp, or a mix of both for versatility.

Cost.
Electric tanked heaters are dirt cheap, and gas fired tank heaters are not far behind when compared to tankless heaters.
Electric tank heaters need no venting making the install 1/4 the cost of gas fired models.

Nat
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Old 07-17-2015, 04:00 PM   #22
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Thanks, Nat. I think that's a very fair assessment. The only minor thing I'd disagree with is the cost comparison for gas fueled units. The residential tankless (above the EccoTemp grade) will all be 95%+ efficient, have sealed combustion so no unconditioned make-up air has to be introduced to the building, and the exhaust is condensing so they can vent horizontally and with plastic pipe. The substantially cheaper $300 tank type gas-fueled will probably be what, 75%-85% efficient? It'll also require make-up air and a vertical metal double-wall vent stack. The cost for a gas fueled tank type with mid-90% efficiency comes pretty close to the cost of the tankless, or at least it did when I compared condensing-type sealed combustion direct vented tank vs tankless for my own house several years ago.

Some of the considerations don't apply when one starts looking at RV-specific heaters... the gas fueled types are (nearly?) all abysmal for efficiency, and since they install against an exterior wall they're all effectively "sealed combustion" and "direct vented."
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Old 07-17-2015, 04:15 PM   #23
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Join Date: Aug 2011
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Your right about the efficiency's of the lower cost gas fires tanked water heaters.

I didn't cover the high efficient tanked water heaters due to the cost. They start at $3000 where I live.

Also the size. So far, I have never seen a half size, gas fired, high efficiency tank hot water heater.

IMO the simple, 1 or 2 element electric tanked water heater is hard to beat for most skoolies.

However, even the low efficient gas fired tanks make great boilers for off grid, low cost, hot water heating, and hydronic space heating.

I have a post in my other thread about the low efficient propane tanked hot water heater that heats a 16 by 26 foot cabin. This coming winter will be it's forth season. Every year it needs a thermocouple but so far, nothing else.

Cost, $50 a month in our brutal winters.

Nat
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