Tankless vs Tank Water Heater

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Which one is better more efficient and what are the pros and cons. Matt
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Matthew Martin wrote:

Tankless take up less space and have unlimited capacity. Tankless also don't use any fuel if you don't use them (unlike tank heaters which keep the water hot if you don't turn them off when you go on vacation).
Tank heaters don't have better efficiency unless they are the heat pump type.
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Tankless Ng have an Energy Factor of between 82-90+ Sears best Ng tank is in the 60s. Ng tankless have bottom efficiencies of 82% and Takagi TH1 is 94%. Few tanks match this. Tankless have no tank to rust out and can last 30+ years, Tankless Ng have no standby loss. Downside is your gas supply must be measured with competing apliances on and factor gas pressure variances in pipe sizing or you may never get 100%., or be sure your gas is adequate before you purchase one and that you know how much your pipe instal is. Tankless do not turn on at low flow maybe 1/2 gal so you may have cold comming out. But the savings I get from a Bosch 117000 btu give me a 4-5 yr payback so it is worth it. If you have kids the unlimited HW might just cost you more. Im sure a reapair could be expensive on tankless.
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Sorry tankless are a looser:( costing over a $1000.00 bucks with a 10 or 12 year warranty the savings on gas if they occur at all will probably never cover the extra cost of the heater. Since you can buy a 12 year warrantied 50 gallon gas water heater today for $330.00 from Sears
beyond which unlimited hot water can lead to much longer showers costing even more. teenagers espically....
Plus theres another issue:( temperature control may lead to temp bounces while showering. others have reported that here, and you may have to upgrade to larger gas pipes to support the large amount of gas needed.
You need to size the heater to the MAX flow needed, like showering, and running a washer. you have to consider the temp increase needed. in cold climates thats more of a issue and varys depending on season.
to sum up the initial cost of tankless is so great the gas saved by no standby looses is less than the addedcost of the tankless.
you can best save $ by buying a really good standard tank, adding a extra insulating blanket, and insulating the hot water lines....
beyond which if you live in a cold climate the standby heat lost in a regular tank isnt wasted as it helps keep your home warm
sad to say tankless sounds nifty but is a lose lose purchase
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There was a fairly lengthy thread on this very subject titled "My new Bosch is a joke...!!!" that began on 2/16., started by someone called SanDiegoGuy. See if you can find it and read all the responces. Very interesting, mainly about the problems with flow vs. temp, as a previous poster mentioned. I do not know anything about Usenet on a computer, but WebTV stores 1500 postings on this group and these particular ones are very near the end, and about to be dropped off as more new posts come in. Larry
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Google keeps all the Group posts, you can google for the Topic...
http://groups.google.com/group/alt.home.repair/browse_frm/thread/b60e0cc33494c815 /
I've heard Bosch is a Joke, though that is just the Bosch Line of Tankless. From my research, the Takagi is the unit you want for the DIY Guy. If you are going to have someone else install the unit, go with the Rinnai.
There are some issues With the incoming Water Temp and Max temp rise for the flow you need. With The Higher end units you can get a remote panel to help smooth out the temp flux.
You need to look at how many potential things you will use that want hot water all at the same time. 2 showers and a laundry cycle is pretty tough without spending atleast $1600.
I'm going with two 4gpm @ 70 degree Temp Rise units. One for the 2 Bathrooms, the other for the rest of the house.
Scott<-

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Really :-) So 100 gpm at 120 F is no problem? :-)

I''ve heard that some tankless heaters keep a small part of themselves warm all the time.

That's true for electric heaters, but a well-insulated tank with a small gas burner can be more efficient than a tankless with a larger burner for the same capacity, measured in gallons per day.
Nick
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On 2006-02-21, snipped-for-privacy@ece.villanova.edu wrote:

Why do you say this Nick? Is the thermal effiency of a small gas burner greater than the thermal efficiency of a large burner? If not, I don't see anything wrong with the usual argument that a tankless unit has greater overall efficiency because it has no standby losses.
Thanks, Wayne
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Maybe not. A 100K Btu/h tankless with 90% efficiency would waste 10X more heat (10K Btu/h) than a tank with a 10K Btu/h burner with 90% efficiency, but it might only run 10% of the time. Given the same size heat exchangers, the tank heat exchanger with the lower firing rate would be more efficient.

IIRC, some tankless units have standby losses.
Nick
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Nick you old ignorant fart, look at published, verified,"Energy Factor" ratings on tank vs tankless and explain it. Go back to your "lightbulb sauna", in your "flooded basement for humidity" you ignorant moron.
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Matthew Martin wrote:

Neither is better, it is apples and oranges.
Tankless is less well understood and usually involves more original cost yet lower operating cost unless they have maintenance problems.
Tankless can deliver hot water all day long while tank types will run out. However tankless can't provide large volumes of hot water, if you try to use too much too fast (maybe a shower the washing machine and the dish washer all at the same time, and you did not size the tankless to handle all three (especially this time of year when the incoming water supply is likely to be very cold) you will not be able to maintain the high temperature, but the tank type would, at least until it emptied the tank.
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On Mon, 20 Feb 2006 18:33:07 -0500, Matthew Martin

Wow! You really put a lot of effort into that question, didnt you Matt? Would you like fries with that? Ever think of trying Google and maybe doing a little homework on your own? Bubba
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If the original poster wanted a better supply of hot water rather than saving energy.
you can but a regular hot water tank with larger capoacity like 75 gallons and a bigger BTU burner. regular burners are around 40,000 BTU, high recovery like 75,000 BTU. these tanks while costing more are still less than a tankless, while supplying a much better supply f nice hot water.
thats what I did, in 2000, it cost a 200 more than a regular tank but we have been very happy wih it.
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Its to bad every "knowledgable" person here hasn`t had any tankless experience but think they have enough knowledge to comment with accuracy. I have a Bosch 117000 btu, It takes 4 gpm incoming and gives a hot shower no matter what is used even at 33f incoming. If incoming gpm match temp rise needed it does not matter how many faucets are open. For savings I have 25$ a month over a foam insulated with extra fiberglass blanket Rheem. So it saves me apx 275 a year, that is pay back. Gas tanks have low certified Energy Factors, standby losses up the flue cooling the uninsulated part of the tank are tanks weakness in design. As far as stability in temp, that is not an issue with proper water gpm and Ng sizing, But how many people actually measure incoming water Gpm and know their peak flow, how many use a manometer with competing appliances on and factor in the suppliers low pressure tolerances. If these issues were known improper installations and Tankless bad mouthing would not occur. It all boils down to ignorance.
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thing.
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Matthew Martin wrote:

Just be aware that you will never ever recoup the initial costs of a tankless from energy savings.
Tanks have better high flow rates and more even temperature, but will obviously run out if emptied of hot water. Tankless provides a smaller amount of hot water continuously, and may, as an unintended consequence, make you sit in the shower longer, either because you can, or because the water might be cooler. Many people stay in the shower until they get "warm enough".
Numbers on real-world efficiencies of tankless versus tanks are a subject of a lot of debate, and are hard to verify, so beware.
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A couple more things: Tanks have hot water ready to go, whereas a tankless has to heat up the pipe first, and so all things being equal, you'd have to wait slightly longer for a tankless located in a central location.
On the flip side, this points to physical limitation on a high-intensity tankless. The moment you shut off the hot water, the intense heat in a tankless has to go somewhere. The options are
1.) Into the now stationary pipe water, where, if the leftover heat is intense enough, it can heat the water to dangerously hot levels.
2.) Into the air.
3.) Both.
Obviously for safety reasons & material reasons, there's going to be a heat intensity or heat transfer rate limitation for the instant-of-water-shutoff condition.
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snipped-for-privacy@hotmail.com says...

At least on my Takagi, which can run the shower, dishwasher, and laundry at the same time comfortably, the moment the water stops flowing, a blower in the unit cools the heat exchanger and clears exhaust from the flue. Maximum heat output is rated at 185,000 BTU.
As with any modern water heater, the system also has a temperature/pressure relief valve, so if the blower fails to run and there's a dangerous heat buildup, the system vents rather than exploding.
One other convenient thing, noticed during a recent power failure. The unit needs 120v 0.8A, only while running, which means that during a power failure it can easily be powered with the inverter I keep in my car for my laptop. Might not have heat or lights after the storm, but I can have a hot shower!
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snipped-for-privacy@phred.org is Joshua Putnam
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Matthew Martin wrote:

I'll try to be more specific. I am currently in the process of buying a house. Right now it has a 40 gal electric water heater. It happens to be in the kitchen. Further down the line I wanna upgrade possibly to a larger one and move it my plan is to either move it to a closet in the hallway or to the garage. Energy cost wise I was trying to figure out would be the better choice.
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Electricity for most of the U.S. is still 50% or so more expensive than N gas. My 25$ a month savings is junking a great electric tank and going Ng tankless, whick now costs 4-6$ a month. People who post of no payback with Ng tankless have no idea of the facts. Either way junk the electric unless you pay .06 kwh., but true efficiency is the "Energy Factor" rating, not just burner efficiency %. Shop with that figure, Energy Factor, and Ng tankless are the highest by 18-25 +%
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