OT: Tankless Hot Water Heaters?

There is an excellent overview of water heaters, tank and tankless in the recent issue of Fine Homebuilding's KItchen and Bath Edition. The most recent issue Fine Homebuilding discusses tankless and it's inherent problems, along with fixes are discussed in the issue.

Sorry, I can't give all the details-- a complicated decision which include: number of occupant (and teens), lifestyle, length of intended residence (high upfront cost), increased gas supply lines etc.

Good Luck

Dustin

There are two kinds of "tankless". Traditionally it has meant a heat exchanger coil in a hot water heating boiler. Now, it can mean a point-of-use in-line heater. Which do you mean?

Bob

We installed an Aquastar Tankless whole house water heater in our house some years ago. It was the 125,000 btu model. It cut our gas bill big time. They are faboulous!!!!!! We LOVED IT. You will love it. Never run out of hot water again. Take a shower for

4 hours if you want to, no problem. I used to hook a water hose up to the hot water faucet at the washing machine and fill the 8 person hot tub with hot water. 100 deg. They are great! You'll never go back to a tank type water heater again. Tank type water heaters are very in efficient. The aquastar had a 10 year warrinty on the heat exchanger and 2 years on everything else. Great Company. I think Bosch owns them now. Current house we live in is 100% electric so I don't have a tankless water heater in this house. Bummer. Dan

In our new house we installed two Rinnai units and I like them a lot. The only water you heat that's not used up is what stays in the pipe after you shut off the faucet. I'd buy them again.

Kingfish

My daughter installed one last year. massive reduction in gas bill. Only negative I can tell, is that if you only turn on a trickle of water ( like for shaving), the flow isn't enough to kick on the burner.

Other than that...high praise... When my tank one finally goes, it will be replaced with a tankless.

al in colorado

It depends on what part of the country you live in. If you live in an area where it is heating season most of the year a lot of the perceived inefficiency of traditional hot water heaters is just heat the is leaked into the house that you would otherwise have to produce with the furnace. However if you live in an area where most of your energy is spent cooling than it might be a different story.

It really comes down to trying to make an educated guess as to what your savings might be and multiply by the expected life of the hot water heater. Then you have to decide if the ROI is in a reasonable range. Personally if I can't see an ROI within 3 - 5 years I don't do it.

Steve

Friends have them. They are good as long as you don't try to do too much at once. One sink and one major appliance at a time on the "small" 125K BTU ones, or you have to upgrade to the "large" 199K BTU unit to run two major items at once.

If you are installing an inside vented unit you HAVE to follow their venting and spacing instructions and make sure that the vent draws properly, they are creating a lot of heat in that box. If the vent isn't as called for or the clearances are compromised, you could light the framing on fire. This is bad.

Next tank water heater that dies here will get a tankless direct vent and the sheetmetal closet goes away. The prices have finally come down to where they pay for themselves.

The Master Bedroom end of the house gets a "small", that's feeding one and a half baths. The other end has the Kitchen, Dishwasher, Laundry and a full bath, that one gets a "large".

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Definately worth the extra costs to install one. We put a Takagi TK-1 in to replace two electric tank units last year. We went with the LPG version and couldn't be happier. A quick check on the numbers shows that it will recoup the extra costs alone by time it has been installed about 14 months. We refill the 100# propane cylinder that powers it, about every six months or so. We cut about 45$ off our electric bill every month and if we could have waited a couple of weeks and dropped a bit more cash, would have gone for the unit that generates it's own electricity for the ignition and blower.

Couple that with the tax rebates and we end up being out something less than 250$ for the unit and installation.

Definately read the install parameter sheets and graphs for outlet temp vs flow vs inlet temp. It takes a little bit of graph reading and number crunching to run the numbers for the correct sizing.

The only negative that I can say, is that it takes a few days to get used to having what sounds like a mini-jet with a very low volume, running on the bathroom exterior wall. We didn't account very well for having the wall resonate a little bit with the unit hanging on the exterior side of the wall. The unit i s so quiet though, you can hold a whispered conversation standing right next to it.

We will definately put one in as a booster for solar water heating in our next house.

I disagree Steve, the heat lost from a conventional water heater is up the stack, not lost into the house.

I could only do one thing at a time in our house as it was so there was no real change there. My two cents, Dan

And I disagree with "up the stack". The Riello burner on my furnace has a door on the air intake that shuts when the burner is not running. Some stacks are equipped with a damper that shuts when the burner is off. From what I have read, unless one has very expensive gas or electricity, the cost of the tankless heater will likely not be paid off before the heater wears out.

============= Not about tankless water heaters, but some information about reducing energy use, including computers, wall worts, and HE lightbulbs. 40 mb file

Title: Energy Saving URL:

Unka' George [George McDuffee] ============ Merchants have no country. The mere spot they stand on does not constitute so strong an attachment as that from which they draw their gains.

Thomas Jefferson (1743-1826), U.S. president. Letter, 17 March 1814.

Kingfish,

Can you get 115+ degree F water out of the tap. I read one manual that stated that it would do an increase of 50 degrees at 4 gpm. That concerns me in the winter time. That would indicate some tepid water on a cold day.

Jay

snipped-for-privacy@spam.net wrote:

Steve,

I live in Texas so I don't have much of a heating bill. The current water heater is electric. I have a 3/4" gas line I can connect to the new heater and gas is much cheaper here. Economically it seems to make sense. I am trying to figure out what I got to give up to get the possible savings. I lived in Europe for a while 30 years ago. The tankless heater were pretty lame then. I presume the technology has advanced some. I just want to make sure I can have really hot water when I need it.

Thanks

Jay

Steve Potter wrote:

I live near Toronto and installed a Rinnai with a buffer tank. I can do about 4 gallons/minute all day if I need to.

The ability for everyone in the house to take a shower in the winter time is priceless.

tom

The house I rented while building my workshop with "apartment" had an electric version of tankless water heater. When it worked, it was OK, but there were times it had some issues. Yes, you can run hot water as long as you want, but make very sure nobody flushes while you're in the shower, unless you like significant temperature fluctuations. They are extremely sensitive to pressure and flow variations. As they age, particularly some of the electric ones, the sensors and/or controllers get fussy, and you may end up replacing one just because of the temperature variations. It's really a pain when the goofy thing trips out while you are in the shower and the water goes cold on you. People I know that have gas fired, high capacity ones don't seem to have the same problems (or won't admit to them), but the purchase cost is considerable, compared to an efficient, well insulated tank heater. Moving from the rental with tankless to our apartment with an 80 gallon, high efficiency electric tank dropped our power bill by about $40 per month, and only two people in the house. By the way, our electric rates here are nearly 33 cents per kilowatt hour, and propane is about 3.50 per gallon. Anyone serious about saving energy here tends to go to solar...

If you do consider one, be careful about the capacity. Most people cheap out and get one with minimal water flow. Typical spec is somehting like a 50 degree rise at 4 GPM. Try drawing 5 GPM and you're lucky to get a 35 degree rise, and that just doesn't cut it. If you do go under-sized, you have to watch how you fill things... For example, a

2.5 Gallons per minute restricted flow showerhead might be OK, but if you try to run a "HOT" load on the washer or fill a tub (That can flow as much as the pump will supply), the water will be barely lukewarm. If I were doing it, I wouldn't even think about anything rated less than 10 GPM, to provide the head room for the variety of pressure/flow conditions for the typical house....

They sound good on the surface, but unless you make sure you have enough capacity, they can be miserable to live with.

Most people that like long showers tend to spend at least as much on utilities even with good efficiency of the tankless, because instead of a 10 or 15 minute shower, it goes on a lot longer, and they end up paying more overall (less per minute, but more overall).

The inefficiency typically quoted for most tank heaters is because of the heat loss while the water isn't being used... In the new building, I put in a high efficiency heater to begin with (high efficiency is simply a matter of more effective insulation), then built a closet around it and provided more insulation. On the typical tank heater, you can feel that it's warmer than the room. A higher efficiency one loses less heat and is cooler to the touch. Providing additional insulation and a draft stop of the cabinet really helps out. If I could figure a good way to get an automatic damper system that was really effective, I might think about a gas heater for the new house.

If this isn't for new construction, be aware of the plumbing and flue issues for adding gas if you aren't replacing a gas tank heater, and if going for an electric tankless, bear in mind these things take an extraordinary amount of power (even the low volume ones need a 50 amp circuit) and you'll need some significant wiring changes to make the change.

--Rick

Dan,

You may be correct that a certain amount of is lost up the flue when the water heater is not running, but consider the surface area of the inside of the flue compared to the surface area of the outside of the tank. Also if loss up the flue is truly a big concern, an automatic damper is far less expensive (and less complicated) than an on-demand hot water heater.

I only live in a two person household, but during the summer months when the only thing using natural gas is my hot water heater my usage is approximately $7/month so as you can see it would take a long time for me to recover the cost of a tankless unit.

Also if the in efficiency of traditional units is because of "idle" time when the hot water is just sitting in the tank, as your usage goes up, your efficiency should increase (less idle time).

Steve

On Fri, 16 Nov 2007 19:18:11 -0800 (PST), with neither quill nor qualm, Steve Potter quickly quoth:

Aren't the new gas heaters pilotless and auto-damped?!? Where's the loss?

There's less loss if it's well insulated, but if you have a tank of water just sitting there simmering all day and night, there will always be some losses. The damper reduces the stack losses, but can't eliminate them. And you can only wrap so much insulation around the outside of the tank - you can't insulate the bottom or you cut off the combustion air.

With an instant heater, if there's no demand for hot water it's stone cold. And it doesn't take any energy to maintain that cold - unless you count a frost protection circuit. (Which is why you want to install it indoors in snow country - milder climes can mount the water heater outside direct-vent.)

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Jay,

I had never checked mine until this morning. My well water was 59* and the Rinnai was set at 120*. The water from the faucet was 117*. I bumped the control up to 125* and 130* and the water temp rose accordingly. (the control panel was still off a few degrees each time). My unit's rating is 4 gpm @ 90* rise and I think it will probably do it.

One interesting thing I've noticed between the two units I have is that the exhaust from the inside-mounted unit is not as hot as that from the outside-mounted unit. You can hold your hand over one and leave it there but the other one gets a little too hot. I wonder if one is doing a more efficient job than the other one.

K>Kingfish,