Your experiences with tankless water heaters

I currently have a 10 year old electric water heater. I’m considering switching to tankless. An electric heater will require an additional circuit. The reviews that I’ve read about them aren’t exactly stellar. They don’t have the capacity that a gas tankless system does so I’m thinking about gas. I already have gas in the house but not to the closet where the heater would live. I got an estimate of $3500 to have one installed. That’s a turnkey job. I’ve read that even with pumps, it can take a long time to get hot water from one side of the house to the other as it would have to in my case.

If you have any experiences with tankless systems, I’d like to hear them. Thanks.

I’ve had tankless systems in several of the houses I’ve lived in and I love them. It is infinite hot water so I can shower after my wife in the morning and still have all the hot water I want. The biggest downside occurs in winter time where the tankless systems are only rated for a particular delta T like 60 if I remember correctly so when the water coming into our house is <40F we couldn’t get hot water anywhere in the house at any time. We’re going to switch to tankless in our current home once our water heater dies but we’re going to install two of them in series so I can get hot water year round.

As far as your concern about taking time to get hot water across the house you could insulate your pipe or install a loop in you hot water lines that would circulate the water in the pipe when you aren’t using it. I’ve never noticed that it takes any longer to get hot water with a tankless system then with a conventional water heater.

Isn’t this the same concern with a tank water heater?

It’s my understanding that tankless isn’t exactly instant. I’m not sure how long the delay actually is.

According to this old house it take about 15 seconds to get up to temperature which in my experience isn’t noticeable. Maybe if you were cheaping out with a very undersized unit it would be worse.

Not quite. I have a small 30A 220V tankless system in my current kitchen on a ~25 foot run. As you imply, the flow time of water through the pipe run is the same tanked or tankless. But it does take the electric heater maybe 30 seconds to get fully up to temp whereas a tanked heater would be moving fully hot water into the pipe from the very first second.

A different issue with gas tankless systems is they take some time to ignite and also some time to heat up. So their reaction is even slower than an electric tankless although they have theoretically a greater heat output.

One side effect of this reaction time is that tankless are not very good for intermittent loads like a dishwasher or clothes washer. Those machines consume hot water in brief pulses. And may never receive any actually hot water despite being downstream of a tankless system on a short run. Doubly so for gas tankless.

Overall I’m happy with my tankless system for the kitchen. Although the biggest advantage is the space I gained in the closet, not its performance at heating water which is merely adequate. I’d prefer one with more oomph, but that was all the electrical capacity available. I have a conventional tanked heater feeding the bathrooms precisely because I didn’t have the ampacity to install a suitable tankless heater for those loads.

Ours is oil-fired. During the winter if we want a shower we bump the thermostat up to about 80. The heater starts heating extra water to increase the temperature in the house; we take a shower, then turn the thermostat back down to its usual 55-60.

Here are two threads from 2015 on point. There’s doubtless been some progress in tankless systems since then.

Mar 2015:

This thread also references even earlier threads.

Dec 2015:

I’ve lived in a house with a tankless gas water heater, and the delay is quite short, hardly noticeable.

As I understand it, many dishwashers heat up their own water. Clothes washers I’m not sure.

Depends on make, model, and age. My dishwasher is cold water input only. My clothes washer has hot and cold inputs but also has a built-in pre-heater on the hot water side to ensure the right temp goes into the drum. Despite being fed by my rather underpowered electric tankless heater, my clothes washer seems perfectly happy with the hot water it’s getting.

OveralI I suspect that tankless HWHs were a lot like low-flow toilets: the first couple years’ products were substandard then the manufacturers broke the code on making sucessful products. Meanwhile the pro plumbing and DIY community persuaded themselves that all the early teething pains were Eternal Truths. The fact the internet never forgets means there are plenty of DIY horror stories from 2007 still findable via Google.

Nowadays I think the systems work well and most plumbers are OK with them. Which is not to say they’re drawback free; every device of every kind has tradeoffs. It may just be a different set of drawbacks than those we’ve accepted for decades with tanked heaters.

I had to replace my water heater last year, and looked into tankless heaters.

One thing that I read from several sources is that it was advised that one should use a water softener with a tankless heater, in order to prevent mineral deposits from accumulating in the heater. We don’t have a water softener, and as we were in an emergency replacement situation (the old heater had sprung a significant leak), I didn’t want to have to make it an even bigger project.

That totally makes sense to me. Interestingly, I bought a house in 2016 that was new construction with a tankless gas water heater. There were hookups in the garage next to the heater for a water softener. The flow to the water softener was from the tankless system to the rest of the house. I guess they didn’t get the memo. ¯_(ツ)_/¯

Wait, no. That doesn’t make sense unless only the hot water were softened. The softener must have been before the tankless heater and it just wasn’t obvious from the exposed pipes.

I have had basically only bad experiences. The problem I have had, with showers in particular, is temperature stability caused by hysteresis and interaction between pressure and temperature. Adjusting the pressure changed the temperature and then you had to change the temperature and that affected the pressure, which affected the temperature and so on. It is entirely possible that things have improved.

I had a Takagi tankless propane system put into the shed when I built it–I intentionally wanted to keep as many crucial systems off the electric grid as possible. Hence the ventless propane heater, vented water heater and gas range. The Takagi I bought was about $700, with maybe a couple hundred in installation costs that included cutting a hole for the vent to the outside through the wall. The thing is lovely, all the hot water one could ever want and so far no matter how cold the inlet water (and according to the Portland water bureau, it gets down to 37F sometimes in winter) the heated water is always plenty hot. Seems quite economical, too, since heating is the major consumer of propane around here and I generally don’t have to fill the 100 gallon tank between about January and September/October. Doesn’t take up much room in my tiny house and I am never going back to the big stupidy round tank again.

I understand that if you have a long way to travel to serve your entire house you might want to consider putting small point of delivery units in far flung bathrooms to cut down on water waste. My house is 14’x36’ so I don’t have that problem.

I do not have gas.
And the cost of rewiring the house makes this a no-go.

This house we bought last year had an electric tankless already installed. I do like it but it’s not without its downsides (and I have no idea of the model or how old it is).

Or house is long and narrow, with the heater at the opposite end from the kitchen. It takes so long to get truly hot water to the kitchen that I’m considering putting in a small unit just for the sink. We’re on a good well so it’s not running up my water bill, but I hate having the water running for no real reason.

It may also be the well pump effect that causes a bit of fluctuation in temperature. It’s not drastic enough to freeze or burn you in the shower, but it is noticeable at times. The bathrooms are very near the laundry room where the unit is, so they get hot water pretty quickly, but the temp isn’t 100% constant.

This describes my parents’ ongoing experience with tankless. It’s been a disaster from day one, with (as of this weekend) a total of 12 service calls and one complete replacement with a newer model. I still cannot get through a shower at their house without constant adjustments to counter sudden cold, followed by scalding hot. They’ve had to reduce the max temperature to avoid burns, and that limits the capability even more. I’ve been a regular guest for decades, and can see no difference in “time to hot” from before.

Based on their experience, this falls under the “not only no, but hell no” category for me. I doubt I’ll ever be convinced to try them.

It sounds like you have what is called a hot water coil which is part of your furnace, and not a tankless system, though you are using it without a tank. But that is a different type of system than discusses here.

It takes longer for the hot water to show up because, first, it has to start up, which takes a few seconds, and second, because the water in the line is completely cold. With a tank, the tank is heating the water in the tank, and some amount of the water in the line.

The other issue is that they have minimum flow rates before they turn on. So, when I’m doing dishes, I have to keep a certain amount of hot water flowing or it will turn off, and the water goes completely cold again. I’ve had that problem in the shower, when switching from two shower heads to one – I think they sometimes just both go off.

The other issue I had was that the output vent wasn’t installed properly, so moisture from the outside was dripping back in and it ruined the heat exchanger. Make sure whoever is installing it really knows what they’re doing – there should be a moisture drain off the side of the output vent to capture that moisture and drain it out the side.

You’ll have to get annual maintenance, or do it yourself. That involves using a pump to pump white vinegar through the system for about an hour. We have a water softener and still have to do this annually.

Because of the drain issue, we ended up having to replace ours at about the 10 year point. That’s where you might have to replace a tank kind, but tankless are much more expensive and are supposed to last 20 years. We’ve replaced the tankless with new ones, properly installed, and hopefully they will last longer now.

You just adjust to the delay in hot water – I’ll get the shower going while brushing my teeth, so it’s ready to go when I am. I definitely use more water with a tankless, but much less natural gas, since I’m not keeping water hot literally all the time, when at work, on vacation, etc.

The endless supply of water is nice – we have a pretty big jacuzzi-style tub, and someone can take a bath while someone else is taking a shower, and there’s still an endless supply.

I would do it again for the reduction in energy use, even though I use more water. Water use is not really an issue in NJ, but CO2 is an issue everywhere.