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Experience with tankless water heater?

Jim Nazium

Jim Nazium

Jun 19, 2007
2,622
3,891
Loudoun County VA (DC area)
#1
I'm going to need a new water heater soon. I was thinking of going tankless, since I live alone and travel a fair amount. The HVAC tech I normally use said they have a lot pf problems and recommended a standard tank heater. Somehow he didn't sound convincing - just a gut reaction, but I wonder if they really have problems or this HVAC guy just gets a higher markup on the old variety.

So, do you have one? Any problems with it? Is it cheaper to operate?
 
#2
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#3
Retired plumber here.

A quality tankless water heater properly installed and maintained is superior to a conventional water heater in nearly every way. The only downside is that they require power to function. So, during power outages, no hot water unless you have a backup generator. Other than that, with your travel schedule, a tankless is the perfect unit. They use 0 utilities when not in use, unlike a standard unit constantly firing to keep that tank of water at temperature.
The list goes on.
 
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#4
Have a Rennai system and it seem to work very well.

Not sure if its a product issue or just the kids griping, but every now and then the kids will complain that their water goes cold. Only seems to happen when every shower (3) in the house is running at the same time and the users of the other bathrooms don't seem to experience the issue. The lady of the house showers at temps that would make a fire dragon scream from the scalding and she loves the system.
 
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#5
As above it it’s not the right capacity you could occasionally have a moment of cool water but in my case that’s when the dishwasher and 2 showers are running. Not common. They work and are pretty cost effective to own. Some utilities offer rebates so look that up.
 
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#6
It's important to be sure and buy a unit with a bit more capacity than you think you need, kinda like "headroom" for your tankless. Also, there are little quirks that are not deficiencies of the units. "Cold water sandwich" is common complaint for someone new to using a tankless. This is a slug of cold water between hot water already in the line from say, someone who took a shower 10 minutes prior, then you get in and a minute later you get a little cold water shot. There is a flow switch that activates the burner so a small amount of cold water gets by before being heated.
There are, of course, ways around this if it's a big deal to you, but those cost money and diminish the fuel savings that you would otherwise see switching to a tankless.

One other thing I forgot to mention. If you go the tankless route, which I recommend, be sure to have the service valve kit installed with the tankless. This allows the unit to be isolated from the house piping while providing valved flushing ports to do an annual flush of the heating coil. VERY IMPORTANT.
That flushing is really the only maintenance these units need unless you purchase a high efficiency condensing heater, you'll need to replace your neutralizer media every so often.
Sorry, I got carried away...:D
 
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#7
Make sure your natural gas supply can handle the tankless. You will need a lot of gas for a short period of time. My cousin got a tankless and found out the hard way she couldn't use three stove burners and the oven while someone else took a shower while dinner was being cooked all at the same time. (the oven didn't get hot enough) No tankless for her.

A tankless needs a certain rate of flowing water to determine you want hot water at the faucet before starting the heating process. If you have a water saving dishwasher or clothes washer, you might not get enough flow for long enough time for the tankless to make hot water before the water saving appliance shuts off. My clothes washer accepts a small amount of water, stops the flow, spins the clothes for a moment, then adds a little more water. It does this a few times before the washer is full. Not tankless friendly. But that's for my washer, maybe not yours or others.

The distance from the tankless to the faucets might make a difference. Again, the water has to flow before the heat comes on, then you have to fill the pipe from the tankless to the faucet to have hot water. With a regular tank, you start filling the pipe with hot water as soon as you open the faucet. Keep in mind, the amount of water to fill the pipe run with hot water isn't huge. Pipe diameter times the length of the pipe (or something like that) will show it's only a gallon or two of water. Not the biggest deal in the world, but if you have a large three story house and the tankless is in the basement in a far away corner, the distance could add up. A small one or two story house or condo is perfect for tankless.

And then there is the venting of the exhaust gasses. A tankless might need to be placed on or near an outside wall and might require a direct vent to outside. If your current heater has a chimney flue to the roof, there might be some venting issues. The tankless might need a fresh air supply different from your current heater. Many tankless use a combined intake/exhaust pipe-in-a-pipe setup that might be different than what you currently have. Time to drill a 4 inch hole in the side of your home.

Having said all of that, I replaced my hot water tank last month. 75 gallon tank, replaced with a new 75 gallon tank. My gas bill for hot water only is $30 or less per month. I can't find enough savings over the time before I'm dead to justify the extra upfront cost of the tankless.

Your mileage may vary. Many people have a tankless system and love every minute of it. They can be very efficient and reliable. If your plumber isn't a fan of them, he might not be the best person for future service IF there is ever a problem. Please let us know of your final decisions, and feel free to include pictures.
 
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#8
FRoss6788 said:
"Cold water sandwich" is common complaint for someone new to using a tankless. This is a slug of cold water between hot water already in the line from say, someone who took a shower 10 minutes prior,
Click to expand...
I get this in the RV, when I'm taking a shower. I turn off the water (not totally, just the "almost off" button on the shower head) while soaping, then when I turn it back on there's a few seconds of hot, then several seconds (feels like a long time) or cold, then back to hot.
 
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#9
I've had a Navian unit for 10 years or so. Once in a while, it'll run luke warm for less than a minute and then comes back on. I had to call a repairman after about two years because it was clogged. He told me to clean it with vinegar once a year and I haven't had a problem with it since. Mine's gas, vented through the garage wall and produces acidic water which needs to be pumped into my utility sink. I've had to replace the pump twice. Other than that, I'm happy with it. HTHs!
 
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#10
As everyone else has said, a tankless does require maintenance, typically flushing it annually but go with the manufacturer’s recommendation. Make sure it can get the natural gas flow it needs or you have room for an extra power circuit on the off chance it’s an electric.

A gas unit will require either PVC venting or could require special metal venting which could require some effort to install.
 
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#12
If you have gas, and your gas supply can handle it, great. Others have already covered the maintenance aspect (which can be reduced somewhat by treating the cold water going into the heater.)

If you go electric, you will probably require a service upgrade, or else you'll be limited to a unit that is too small, and you'll get lukewarm water from it. After which you'll go back to a tanked heater unless you are really dedicated to the idea of a tankless, and want to burn a lot of money on that service upgrade after all.

IMHO, if you have electric, tankless is NOT a particularly big win. A modern, properly insulated electric tank has ~1 kWh per day of standby loss, or less. If you're leaving on travel, switch it off when you leave. It won't require a service upgrade to provide adequate hot water. If your climate is suitable, consider a heat pump version, but realize that the common heat pump version adds to your heating load in the winter, so it may not make sense if you have serious winter. But it's some "free AC" if you have serious summer.
 
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#13
I really liked my electric tankless heater at my lake house. Beat waiting to heat up a 40 gallon tank and/or wasting $$$ to heat water that I wouldn’t use.

I had a Steibel Eltron unit. It failed only because it was drawing silt/sand from the lake via my pump system. The tankless heater was just too sensitive for that. The filter would clog regularly and the unit would go into protection mode.

I tried all kinds of filters at source and nothing really did the trick to keep the heater’s filter from clogging.
 
#14
My friends had a tankless with whole-house circulation (sorry, don't know the brand). Over about 10 years it broke down several times. The circulation pump had to be replaced twice. There was some other issue I can't remember. They finally replaced it with a conventional electric tank.

It just seems like there's more things to go wrong with a tankless. I dunno.
 
#16
turf3 said:
I get this in the RV, when I'm taking a shower. I turn off the water (not totally, just the "almost off" button on the shower head) while soaping, then when I turn it back on there's a few seconds of hot, then several seconds (feels like a long time) or cold, then back to hot.
Click to expand...
In our RV we take Navy showers (for sailors, Army showers for soldiers) I get wet, shut off the water, soap up, rinse, shut off the water, shampoo, rinse, done. It’s not so much because the WH can’t keep up, but because it fills the gray water tank faster.
 
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#17
Got one and like it. It takes a little longer for the hot water to arrive at the faucet, but that's not much of an issue now that we are used to it. With a tank, it took a little while anyway. Another few seconds isn't a big deal. I don't remember how long it's been in, but I don't expect problems. A tank will fail anywhere from ten to twenty years after installation. I expect the tankless to last as long as we maintain it because it won't slowly fill up with sediment. One thing to consider is the pipes coming into the house. If they are old, you may end up with some issues from that. We have all new pipes in the house, and a new and expensive line to the meter. What's beyond the meter is City of Seattle, meaning who knows how old it is. At least 35 years, since that's how long we have lived here. Probably a lot older than that. It could be an issue eventually.
 
#18
Ostie said:
In our RV we take Navy showers (for sailors, Army showers for soldiers) I get wet, shut off the water, soap up, rinse, shut off the water, shampoo, rinse, done. It’s not so much because the WH can’t keep up, but because it fills the gray water tank faster.
Click to expand...
Yes, like I said - I don't have to actually turn the shower knob off, I have a "pause" button that shuts it almost completely off. But when I turn it back on, there's a short period of COLD COLD COLD before the WH kicks back in and I get warm water again.

One solution, of course, is to shower in the park/camp facilities, if such are present.
 
#19
I have an electric water heater up in our mountain place. It looks like it might be as old as the building, which went up in ‘82. It works fine but I figure it could go any time, in which case I want to look at tankless since we aren’t always up there.

Which brings me to my question - how much of an issue is groundwater temperature coming into the unit? Our place is at 7400 feet in the Rockies and the water coming out of the tap is butt cold in the winter.
 

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