tankless water heaters.

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dSilanskas said:
You know that is a good question and for the life of me I can't recall. But the plumber was from Ireland and he said before he came to the states that it was very popular over there if that helps you out any:confused:
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Nope... no clue. :-?
 
If you decide to go with the 150 amp tankless heater, you may need to factor in the cost of a dedicated set of lines from the nearest power plant.
 
If the US went exclusively to tankless type water heaters (insta-hot), I don't believe that the current electrical system could provide the necessary power.

The Power company sizes their systems for the Peak demand, which means if there is a very large demand for only a few minutes at a time, they must have capacity to provide that peak demand.
It doesn't matter if it's only for for a few minutes, once daily, the capacity must be there or they (and us) will have big problems.

If things continue down that road, look for more (CO2 producing) generating plants and higher electrical bills to cover that expansion.

We need to look at both sides of the picture before we say that these units are "energy efficient".

Just my opinion
steve
 
mdshunk said:
Same goes for the gas on demand water heaters. If a whole neighborhood installed them, gas pressure would be at a trickle when everyone is getting ready for work in the morning. This warning has been written about in trade magazines lately. The recent article "Going Tankless: Energy efficient hot-water heaters are making inroads in the US market, but when is tankless the right thing to do?", by Penelope Grenoble. This article not only explores the peak demand issue, but also the more common sense payback issue.
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I'm not sure gas company pressure is an issue. I read
this article, and while it raised many issues, I missed
this if it brought it up.

Obviously, the building's internal supply lines
need to be properly sized, but pressure is unlikely
to be reduced to a trickle because there is a problem
on a utility-wide scale

It doesn't follow that the same argument that goes
for electricity goes for gas, because unlike electricity,
gas is stored in the distribution. Because it's pressurized,
the entire distribution system acts as a giant pressure
buffer which evens out the loads. It's not likely that
shorter, larger gas loads would be a problem for the
utility because they have to pump the same daily amount
(or maybe slightly less if these are more efficient),
and they have the entire system as a buffer. It seems
to work just fine on a utility scale overseas.
 
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non-use heat loss, some hard numbers

non-use heat loss, some hard numbers

A medium or small size electric water heater with average insulation during periods of no water usage ran for 5 minutes each 5 hours just to maintain the setpoint. When it was better insulated it went 5 minutes each 7 hours.

This is how many kilowatts you'll be paying for with a tank heater.
 
Lxnxjxhx said:
A medium or small size electric water heater with average insulation during periods of no water usage ran for 5 minutes each 5 hours just to maintain the setpoint. When it was better insulated it went 5 minutes each 7 hours.

This is how many kilowatts you'll be paying for with a tank heater.
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Not this one. "A full size Marathon water heater loses only about 5 degrees in 24 hours!"
Marathon water heater

Then how much heated water is left in the pipe just to cool down after each use?
 
5 degrees in 24

5 degrees in 24

So let's say 3x better insulated than the one I measured.
Ideally, a perfectly insulated tank should be the same cost to run as a tankless.
Your link said "one-quarter to one-third of your monthly electricity bill" but our localpocoPepco says 10%; I'd think the poco is more impartial on this number.

That link said a lot of bad things about the tankless heaters, but somehow the Europeans use them. Sounds like the hidden cost-of-ownership is pretty high with these things.
Maybe the European countries save energy with these but the penalties are shifted to the individual homeowners who assume the burden of short service lifetimes.

But the convenience Americans have come to expect may outweigh all of the financial aspects of calculation.
 
hillbilly said:
If the US went exclusively to tankless type water heaters (insta-hot), I don't believe that the current electrical system could provide the necessary power.

The Power company sizes their systems for the Peak demand, which means if there is a very large demand for only a few minutes at a time, they must have capacity to provide that peak demand.
It doesn't matter if it's only for for a few minutes, once daily, the capacity must be there or they (and us) will have big problems.

If things continue down that road, look for more (CO2 producing) generating plants and higher electrical bills to cover that expansion.

We need to look at both sides of the picture before we say that these units are "energy efficient".

Just my opinion
steve
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I don't think that on a large scale, their demand on a neighborhood sized grid is any more than it would be for typical traditional tank heaters. Not everybody wakes and showers simultaniously. With tanks, a good 10 minute shower will leave your electric tank reheating for a good hour.

So 60 showers in 60 homes increases the load on the grid for 60 minutes, as much as 10 simultanious showers in 10 homes increases the load for 10 minutes...

What I'd like to know is why every central A/C unit can't be piped to heat a tank of domestic water before wasting that heat to the outdoors. It amazes me how some people will be air conditioning the house, while using another heat pump to heat the swimming pool...
 
SmithBuilt said:
Not this one. "A full size Marathon water heater loses only about 5 degrees in 24 hours!"
Marathon water heater

Then how much heated water is left in the pipe just to cool down after each use?
Click to expand...

Wouldn't a tankless have leftover heated water in the pipe after each use as well? To avoid that, on a large scale, you'll need a tankless at EACH point of use. Now balance the costs of running 6-4awg feeders all over for tankless units, (assuming electric tankless) plus the unit costs themselves, and the payback for eliminating unwanted radiant heat is well into the next century. Using gas tankless, well, gas piping and flue aren't free either, and I bet they're higher maintainence.

IMHO you cannot beat a standard gas or electric water heater for their pure simplicity and their cost. Energy codes require they be super-insulated. I suppose a gas model could be more efficient if there was a stack damper, as the internal heating core is where most of the losses occur, though natural draft convection. But that would require power and a control circuit...
 
I am going to jump in on this one as I recently built a home using two TWH?s and did a lot of research before reaching my decision. I wished there was a simple answer to the question or debate, but there is not because there are too many factors involved. I can briefly say if it is now construction you need to consider THW as it may save you money after 5 or 6 year. Replacement or remodel jobs are not likely to ever get a payback..

I will only address new construction as I do not believe the advantages of THW?s overcome the additional cost of replacement of conventional tank heaters.

THW are about twice the cost of conventional. An average 40 gallon heater runs about $500 to $600, and TWH about twice that. If you use the average 63 gallons per day a THW uses about 33% less energy. Savings translated to average therm units for NG are about $100 per year, so ROI is 5 to 6 years. Installation cost in new construction is about the same, so the initial cost deference is in the heater itself. Not true with replacement.

Now here is where the gray area comes, hard water vs. lifetime. If you have soft water the conventional tank heater lifetime is about 10 years, a TWH about 20. If you have hard water a TWH could require costly de-liming once a year or more. Of course this can be solved with water softeners, and if you have a well you might very well already be having to use one anyway.

The last factor is inlet water temps. If you live in the north where water temps are cold in the winter, then you might have a problem.

For me being in TX, new construction, soft water, and cheap NG made it a no brainer. I am very pleased with my setup. One THW heater serves the kitchen and laundry, the other serves the two bathrooms one of which has a spa tub. I can run everything at once with no problems or waiting.

My best advice, some of you won?t like it, is to ask your local MEP, you know, your plumber guy. If he is honest, he should know the area conditions and tell you which is right for you.
 
LawnGuyLandSparky said:
Wouldn't a tankless have leftover heated water in the pipe after each use as well?
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Yes, unless you follow my earlier post. A well insulated hot water loop and circulating pump.


My engineers argument is the total system of the Marathon water heater, circulating pump and insulated loop does not loose as much heat. He also argues that if you install a 100 gal tank and load management you'll get a cheaper rate. There is also a tax credit right now.

The tankless will always have the loss due to the amount of water left in the pipe unless it is at the fixture you are using.
 
SmithBuilt said:
The tankless will always have the loss due to the amount of water left in the pipe unless it is at the fixture you are using.
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How is this a problem since it is purged in seconds?
 
I've talked to a lot of plumbers about the tankless systems. 90% of them say that the electric ones aren't worth a diddly and that gas is the only one they'd install in their own homes. If there was no gas then they'd use propane, if they can't use propane than there won't be a tankless system in their house!

Electric tankless heaters require a higher ground temperature to achieve adequate temperatures out of your water. Gas heaters can heat the water to higher temperatures.

The electric Bosch units have the most complaints.

Rennai gas tankless seem to be one of the higher quality models.
 
water left in the pipe

water left in the pipe

is in there, tankless or not. I think this consideration drops out of the equation.
100' of 1/2" ID pipe holds a gallon of water. This much water may have to be run, but not heated, if the tank is 100' from the point of service.
 
I have given this some thought and it seems (like noted above) more is better in lieu of whole house maybe closer to point of use.
 
tonyou812 said:
Has anyone ever had any experiance with electric tankless water heaters? I had a customer ask me about them. I personally never come accross one. They do not have natural gas available in their area. Im more concerned about if they function ok. Ive heard that some of the gas models dont have a very good low flow rate, meaning that if you have the hot water on just a little the flow sensor dosent always pick it up. Any info on past experiances would be appreciated.
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Yes but not really electric I am posting this just to let you know electric is not your only choice. my friend is a dealer for an oil fired direct vent type it runs on home heating oil and it comes with a plug on it run/95 watts Ignition/125 watts both intake and vent is in a double walled pipe and they are twice as efficient as a standard boiler you will see return very quickly.
 
Lxnxjxhx said:
is in there, tankless or not. I think this consideration drops out of the equation.
100' of 1/2" ID pipe holds a gallon of water. This much water may have to be run, but not heated, if the tank is 100' from the point of service.
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I must not be explaining this very well. You make a hot water loop that is continuous to each fixture(right up to the fixture), you don't have to wait at all for hot water. The circulator pump continuously runs and keeps hot water in the insulated line.

On a conventional tank or tankless without the loop you have already heated the water (1 gallon as you state) that is left in the line after you finish running the water. I have 3/4' lines so more in some cases. Then when you need hot water again you waste the 1or 2 gallons of cold water, that was heated at one time, waiting on the hot to get there.

You may say thats only one gallon but it adds up. Family of four washes there hands I don't know maybe 4 times each per day. Wife needs hot water for cooking several times per day. Then you have wasted 20 gallons of cold water, that once was heated. That's 20 gallons you have to heat every day and not get any benefit from, 1/2 the size of most water heaters.
 
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