Tankless water heater

Diana

Diana

Final Approach
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Diana
Somebody suggested that we replace the hot water heater in the hangar with a tankless, on-demand water heater that just hangs on the wall. We'd never heard of those before. Does anybody have experience with those? I heard that you can get some kind of tax credit if you have one.
 
Paul Harvey talks about the Rennai (sp?) tankless water heater. The tax kick-back might have expired at the end of the year. I haven't heard any of the ads in a few months, but I seem to remember that they kept saying it expired at the end of 07.

From what I've heard, they're good for what you're looking for. Not enough capacity for a family of four to all take showers in one morning while the dishwasher is running, but perfect for small-use areas.
 
That sounds like a great idea.

The energy savings are greater the less frequently you use the hot water (you don't have to maintain a tank of hot water which slowly cools...). Tankless heaters can be powered by electricity or gas... lots of residences in central Europe use gas powered tankless heaters that are so small they hang on the wall over the sink.

-Skip
 
CJones said:
From what I've heard, they're good for what you're looking for. Not enough capacity for a family of four to all take showers in one morning while the dishwasher is running, but perfect for small-use areas.
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Well, you just need to wire the house for 480, and get one of the industrial ones! Shower heads are 3.8gpm I think, I don't know what my dishwasher uses, but get a 10gpm and you'd be good to go!
 
CJones said:
From what I've heard, they're good for what you're looking for. Not enough capacity for a family of four to all take showers in one morning while the dishwasher is running, but perfect for small-use areas.
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They're tankless. They have 0 capacity.

They heat the water as its needed, when the water is flowing, and only when the water is flowing.

How long it runs is irrelevant. How quickly it can heat is what matters.
 
So, the more water you use in a tankless system the less efficient the setup is? Since a water tank uses power regardless of usage that makes sense that there would be a break even point. I wonder what it would be?

I'd bet with a large family a 40-50 gal water heater is still more efficient.
 
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Not really, as I understand it.

With a 50 gallon tank, you have to heat the tank, the you have to keep it heated, 24/7, regardless of usage. It takes a certain amount of energy to heat 50 gallons of water, and the amount of energy needed doesn't change.

Every time you draw on the tank, you add cold water to the mix, so the tank has to reheat that amount of water.

So far, tank vs. tankless, you're even.

However, a tank heater also has to maintain the temp, 24/7. No matter how well insulated, your water heater WILL lose heat. The only way to preserve heat with 0 loss is ...non existent...and with all the pipes going into and out of the water heater, it's nowhere near complete insulation.

Even a large family is away from home, or not using the tank, more often than it is. People sleep 8 hours a day, so that's 1/3 of the week already the water doesn't need to be hot. Work/school 8 hours, there's another 1/3 of the time. So you're paying for 24/7 hot water when you only need it about 8 hours a day, if that. All that time keeping the water hot costs money.

The tankless, however, only has to heat water when its demanded, and it has to heat the same amount of water at the same time, and it takes the same amount of energy to heat that water to temperature.

But it doesn't have to do it when nobody wants water.

So if you buy the *right* tankless heater (enough BTUs), you've got NO issues with capacity, and you are only heating water during the few hours a day a large family might need.
 
The "capacity" issue is all about finding one that will handle the number of "appliances" that you want to use simultaneously.
 
Diana said:
Somebody suggested that we replace the hot water heater in the hangar with a tankless, on-demand water heater that just hangs on the wall. We'd never heard of those before. Does anybody have experience with those? I heard that you can get some kind of tax credit if you have one.
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Is that area always heated Diana? I would be concerned with freezing if not.
Otherwise sounds like what you need.
 
Greebo said:
Not really, as I understand it.

With a 50 gallon tank, you have to heat the tank, the you have to keep it heated, 24/7, regardless of usage. It takes a certain amount of energy to heat 50 gallons of water, and the amount of energy needed doesn't change.

Every time you draw on the tank, you add cold water to the mix, so the tank has to reheat that amount of water.

So far, tank vs. tankless, you're even.

However, a tank heater also has to maintain the temp, 24/7. No matter how well insulated, your water heater WILL lose heat. The only way to preserve heat with 0 loss is ...non existent...and with all the pipes going into and out of the water heater, it's nowhere near complete insulation.

Even a large family is away from home, or not using the tank, more often than it is. People sleep 8 hours a day, so that's 1/3 of the week already the water doesn't need to be hot. Work/school 8 hours, there's another 1/3 of the time. So you're paying for 24/7 hot water when you only need it about 8 hours a day, if that. All that time keeping the water hot costs money.

The tankless, however, only has to heat water when its demanded, and it has to heat the same amount of water at the same time, and it takes the same amount of energy to heat that water to temperature.

But it doesn't have to do it when nobody wants water.

So if you buy the *right* tankless heater (enough BTUs), you've got NO issues with capacity, and you are only heating water during the few hours a day a large family might need.
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They do make timers for your water heater.....I've got one and it does have to be adjusted from time to time.

Mine turns off at bed time and on a half hour before we get up.
 
The two folks I know who have tried them had issues with their relatively hard water. But then again, a regular hot water tank will have "issues" with hard water.
 
I've been using a Bosch Aquastar Tankless for the last 20 years. The only maintenance has been to replace the thermocouple. Basically, the beast sits on the wall and waits until you turn on the water then it ignites and makes sounds like a blow torch on steroids. Hot water hits the tap about a minute later.

You need to size the heater for the number of major hot water appliances you want to run simultaneously. The rule of thumb is that you need a 45 deg temperature rise at 6 gallons per minute to run 2 showers (or a shower and a dish washer, etc) simultaneously.

The biggest plus of a tankless is that you never run out of hot water. The biggest downside is that the temperature rise is dependent on the flow through the heater (the slower the flow, the hotter the water) -- this leads to the "scald-o-matic" phenomenon -- just after getting into the shower temperature just right, some clod will turn on a cold water faucet full-bore thus dropping the flow through the heater -- your shower goes from comfortable to you-can-cook-lobster-in-this in 3.2 seconds.

If you are in an area with hard water, you may want to put a water softener ahead of the tankless water heater. Hard water scale will kill a tankless heater much faster than its tanked cousin -- hey, the thing is basically a radiator sitting over a heat source; plug up one of those little tubes and the thing is tango uniform.

I've been happy with mine and would buy another.

Bruce
 
The biggest plus of a tankless is that you never run out of hot water. The biggest downside is that the temperature rise is dependent on the flow through the heater (the slower the flow, the hotter the water) -- this leads to the "scald-o-matic" phenomenon -- just after getting into the shower temperature just right, some clod will turn on a cold water faucet full-bore thus dropping the flow through the heater -- your shower goes from comfortable to you-can-cook-lobster-in-this in 3.2 seconds.
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I'm not a plumber, but I believe this is caused by poorly designed piping without proper pressure regulation.
 
My FIL has been using a tankless system for as long as I can remember. He has had no problems using it and is on a well.
 
Checkout_my_Six said:
Do they make an electric tankless heater?
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I think they do. I seem to remember an office of ours having one, and it sucking. It didn't have enough power draw to heat the water. I think one that would be sufficient would require 220v.
 
Greebo said:
I think they do. I seem to remember an office of ours having one, and it sucking. It didn't have enough power draw to heat the water. I think one that would be sufficient would require 220v.
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Yeah, and I could imagine the lights dimming with that huge current draw for that few seconds of hot water. Something about that doesn't sound very efficient.
 
Checkout_my_Six said:
They do make timers for your water heater.....I've got one and it does have to be adjusted from time to time.

Mine turns off at bed time and on a half hour before we get up.
Click to expand...

That'll save you somewhat, but still won't be as efficient as tankless. Your water heater is still going full-bore for that half hour before you wake up to heat 50 gallons of water, and is still keeping it that way all day.

The only way for tanked to be as efficient as tankless was if the tank was the exact size needed to hold the amount of water you were going to use, it heated the water right before you used it, and then shut off and didn't attempt to heat any more water until preparing for the next use.
 
I thought about a tankless. I don't think the energy savings is worth the premium in cost.

In my case I'd need the largest size possible to handle 3 baths and a kitchen, even if I wouldn't use them all at the same time now.

Also, when I've seen them installed on TV DIY shows like "Ask This Old House," the contractor usually runs a larger 3/4"(?) gas line because these things need a lotta BTUs. Diana, you may need to see what size gas line feeds the hangar. What timing!: http://www.thisoldhouse.com/toh/asktoh/question/0,,20058415,00.html
http://www.thisoldhouse.com/toh/asktoh/question/0,,213064,00.html

They also, like a high efficiency furnace, have to be vented directly to the outside. The 90% systems put out a lot of moisture that you don't want to run to the regular flues.

I was skeptical that the high efficiency systems don't pay for themselves, but with gas prices guaranteed to skyrocket, I changed my mind. I have one 9?% furnace and I'm amazed how little my gas bill is. The bill is less than half of what I paid in my drafty Chicago two-flat apartment and I have at least twice the volume now. CFI Joe just got a bill that's 3x mine and his house is smaller.

I'll be replacing the second furnace with a 9?% one, but I think I'll go with a high efficiency conventional tank water heater.
 
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Diana said:
Somebody suggested that we replace the hot water heater in the hangar with a tankless, on-demand water heater that just hangs on the wall. We'd never heard of those before. Does anybody have experience with those? I heard that you can get some kind of tax credit if you have one.
Click to expand...

I do have some experience with them, from when I lived in Europe...

Skip Miller said:
lots of residences in central Europe use gas powered tankless heaters that are so small they hang on the wall over the sink.
Click to expand...

...where pretty much all houses were equipped as Skip describes. Every sink, bathtub, etc. had its own mini-heater. Why on earth we in the US still use the big old antiquated tank style is beyond me. With the tankless heaters right near the outlet, you have a lot less pipe to install when the house is built (no hot-water pipes until just before the faucet), and you get nearly instantaneous hot water (WAY quicker than waiting for all the cold water to exit the pipe!), all for LESS energy!

I don't know if anyone markets the tiny tankless ones in the US, but if you can find 'em, they're great.
 
Checkout_my_Six said:
Yeah, and I could imagine the lights dimming with that huge current draw for that few seconds of hot water. Something about that doesn't sound very efficient.
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Doesn't matter. The net use of energy to heat the same amount of USED water over a week is still less.

Again, you're thinking about the problem wrong. It's like the conveyor belt trap.

Given a defined volume of water (assume the average amount a family of 4 uses in one week), it doesn't matter whether you heat it over 2 hours or 2 seconds, it takes the *same* amount of energy to give the same thermal change.

Electric or gas, instant tankless or conventional tank, with equally efficient systems (as in, energy use and heat retention, NOT how much power it uses while running), the energy required to heat 10 gallons of water will be the same.

What the tankless doesn't do is heat all that water when you don't need it. Even if the tankless is slightly less efficient when operating, its STILL much more efficient overall than the tank which is always keeping water hot regardless of demand.
 
EdFred said:
I must be on ignore.
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Makes you wonder, doesn't it. :D Poor Ed.

Thanks for all of the information everyone (including Ed ;)).

I can't help but wonder why these aren't used more since they seem so efficient and take less space and don't leak water all over the place.
 
Greebo said:
Doesn't matter. The net use of energy to heat the same amount of USED water over a week is still less.

Again, you're thinking about the problem wrong. It's like the conveyor belt trap.

Given a defined volume of water (assume the average amount a family of 4 uses in one week), it doesn't matter whether you heat it over 2 hours or 2 seconds, it takes the *same* amount of energy to give the same thermal change.

Electric or gas, instant tankless or conventional tank, with equally efficient systems (as in, energy use and heat retention, NOT how much power it uses while running), the energy required to heat 10 gallons of water will be the same.

What the tankless doesn't do is heat all that water when you don't need it. Even if the tankless is slightly less efficient when operating, its STILL much more efficient overall than the tank which is always keeping water hot regardless of demand.
Click to expand...

Yeah Yeah Yeah... But there is no TANK! j/k ;)

"Did I mention the Tank... is a Tank?"
 
Greebo said:
I'm not a plumber, but I believe this is caused by poorly designed piping without proper pressure regulation.
Click to expand...

I've experienced the problem in 3 different house with 3 different heaters. The only common denominator is that all 3 installations were on private water systems so I had attributed the problem to the fact that a well & pump just don't produce the constant pressure of the average city water system.

I think you can get temperature balancing valves for showers that can compensate for the problem as well.

As for poorly designed piping... well I seem to have an affinity for old farm houses and to say the plumbing is poorly designed is a bit like saying bricks have poor flight characteristics.:D

Bruce
 
Well its not an easy fix and by poorly designed plumbing, I mean most houses built to minimum code and nothing more.

From what I understand, and again, I'm no plumber, there are ways to mitigate those issues but they are very costly.
 
My parents had one installed in their house in Florida a few years back and they love it (it's electric). At the time the guy told them they didn't have any approved for use in the Northern US/Canada. It had something to do with how cold the base temperature of the water gets, thereby requiring more powerful heater elements to create the instantaneous temperature rise and getting the requisite code approvals. I do believe, as Ed points out, that this has been overcome now.

I spend a lot of time in England and second the idea of having a small one attached to each point of hot water use. They work great.
 
cameronbm said:
I've experienced the problem in 3 different house with 3 different heaters. The only common denominator is that all 3 installations were on private water systems so I had attributed the problem to the fact that a well & pump just don't produce the constant pressure of the average city water system.

I think you can get temperature balancing valves for showers that can compensate for the problem as well.

As for poorly designed piping... well I seem to have an affinity for old farm houses and to say the plumbing is poorly designed is a bit like saying bricks have poor flight characteristics.:D

Bruce
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You used to be able to get shower units which had built in pressure adjusters (Moen???). We had them at the cottage where you have a small cold water pressure tank vying with a 50 gallon hot water tank. They were a must - otherwise you froze/boiled as the pump cut in and out.
 
Greebo said:
Not really, as I understand it.

With a 50 gallon tank, you have to heat the tank, the you have to keep it heated, 24/7, regardless of usage. It takes a certain amount of energy to heat 50 gallons of water, and the amount of energy needed doesn't change.

Every time you draw on the tank, you add cold water to the mix, so the tank has to reheat that amount of water.

So far, tank vs. tankless, you're even.

However, a tank heater also has to maintain the temp, 24/7. No matter how well insulated, your water heater WILL lose heat. The only way to preserve heat with 0 loss is ...non existent...and with all the pipes going into and out of the water heater, it's nowhere near complete insulation.

Even a large family is away from home, or not using the tank, more often than it is. People sleep 8 hours a day, so that's 1/3 of the week already the water doesn't need to be hot. Work/school 8 hours, there's another 1/3 of the time. So you're paying for 24/7 hot water when you only need it about 8 hours a day, if that. All that time keeping the water hot costs money.

The tankless, however, only has to heat water when its demanded, and it has to heat the same amount of water at the same time, and it takes the same amount of energy to heat that water to temperature.

But it doesn't have to do it when nobody wants water.

So if you buy the *right* tankless heater (enough BTUs), you've got NO issues with capacity, and you are only heating water during the few hours a day a large family might need.
Click to expand...

Well your sort of right, only if the tank type uses fast recharge. The faster you heat the water the less eff it is. So if you have a slow heating tank heater and a fast heating tankless it's a toss up.

I have a tankless small com around 7 gpm and it works fine. We also use a boiler and you can stay in the shower all day.

What are you using the hot water for? washing hands? Use a tankless electric (very small) but works fine for that. Washing plane? Use bigger 5 gpm tankless. Using it to heat the hanger? Use tank type slow recovery.

Dan
 
Greebo said:
it doesn't matter whether you heat it over 2 hours or 2 seconds, it takes the *same* amount of energy to give the same thermal change.
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Yes it does, This came from my Heating guy when he set up my boiler. The first guy set it up so that it heated the water fast but not as hot, we ran out. The factory rep told me if you heat the water slower but hotter you will save energy. The amount of heat you loose is not that much. Electric time of day heaters hold water temp all day with no problem. My outside boiler holds 160 deg most of the day if it is 40 deg or so and it has almost no insulation.

Dan
 
Diana said:
...

I can't help but wonder why these aren't used more since they seem so efficient and take less space and don't leak water all over the place.
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The current Lowes ad says I can get the best 50 gallon, 12 year warranty, conventional water heater for $399. We can guess a professional install where the existing one is would be $150-$250.

A tankless that comes close to meeting my needs would be $1200, and that would require an additional $500-$1000 to install.

I'd need to save a lotta gas to make the difference back, even if I replaced the old kind again in 10 years.
 
stingray said:
Yes it does, This came from my Heating guy when he set up my boiler. The first guy set it up so that it heated the water fast but not as hot, we ran out. The factory rep told me if you heat the water slower but hotter you will save energy. The amount of heat you loose is not that much. Electric time of day heaters hold water temp all day with no problem. My outside boiler holds 160 deg most of the day if it is 40 deg or so and it has almost no insulation.

Dan
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Sorry but the factory rep doesn't seem to know much about thermodynamics.

Any time you have a tank, you will have standby losses. A tank is, simply by design, less efficient at retaining energy than your standard decent quality coffee thermos. (Too much surface area for conduction).

While it may be true that faster tank heating is somewhat more expensive than slower tank heating because of the rule of diminishing returns, it is indisputable that the energy required to heat 100 gallons by 10 degrees is the same no matter whether you do it fast or slow. Where efficiency comes in is not in the amount of heat itself that goes into the water, but energy lost by other means.

But those rules of faster heating vs. slower heating efficiency are NOT RELEVANT to the issue of tank based standby losses. Your tank type water heater HAS to keep the water hot all day. It doesn't just heat the water then shut off til you use more water, it heats the water, and if you don't use it, it will still kick on again in a while to maintain temp. THATS the energy loss you don't have with tankless.

http://en.wikipedia.org/wiki/Water_heater#Tankless_heaters

http://www.eere.energy.gov/consumer/your_home/water_heating/index.cfm/mytopic=12820

For homes that use 41 gallons or less of hot water daily, demand water heaters can be 24%–34% more energy efficient than conventional storage tank water heaters. They can be 8%–14% more energy efficient for homes that use a lot of hot water—around 86 gallons per day. You can achieve even greater energy savings of 27%–50% if you install a demand water heater at each hot water outlet.
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I've had a gas Aqua Star for almost 10 years. We are on our own well, pump, and pressure tank so have some of the pressure, temp variability issues mentioned. Took a lot of tweeking of pressure and pump regulators to get it to not drop out in the middle of a shower. Single handle mixing valves confuse the issue. If you have 2 valves at the faucet or shower you run the hot full open and adjust the temp with the cold. Always have to brief visitors on this. You gotta keep the hot flowing through the heater or it drops out. It's GREAT for eternal showers which is bad if you have teenagers. Good for filling the hot tub after servicing as I don't have to wait 12 hours to get in. It's all hot right away! If you have a small occasional use simple system without multiple users an electric unit would be pretty good. They are easy to install but pricy compared to the good old tank units.
 
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