WARNING - things you should know about a tankless heater
Written: Mar 01 '08
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Product Rating:
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Pros: Pros: Endless (but limited volume of) hot water, smaller than tank.
Cons: Cons: Temperature surges, expensive, maintenance
The Bottom Line: I would not buy a tankless heater because of the temperature variations and expense. And in my situation I don't believe it will save any money.
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| dkuchta5's Full Review: Bosch AquaStar 125B NG Natural Gas Tankless Water ... |
Note: I don’t own this hot water heater, but I own a similar one. The comments I make here apply to all tankless heaters, regardless of brand. These are things you should consider before making a purchase. They are also things you won’t hear from the manufacturer.
I have had a tankless hot water heater now for nearly a year. I was excited about having endless hot water AND saving money on my bills, so I thought this was a great idea. Now I think we made an expensive mistake.
I live in a 2000 square foot house with my wife and 2 teen-aged kids and we have two and a half baths. We do a fair amount of laundry, run the dishwasher once a day, and everyone takes a shower once a day. We previously had an 80 gallon hot water tank and never ran out. So I was going more for savings than the promise of never running out of hot water.
When we needed a new tank, we had a choice of a new 80 gallon tank installed for about $800, or the tankless installed for $2500. The price was high because we needed one of the largest tankless models, and installation is tricky and much more expensive than a tank unit. But, we were told that we would save money in the long run, and that these things are designed to last a very long time, unlike the 10 year life of a tank.
Hot Water Supply
The first thing we noticed was that the hot water volume available, even when just using one bathtub at a time, was noticeably less than before. Also, an odd startup behavior occurred where the water flow was substantially less for about 5 seconds, and then ramped up to a more useable level, but still less than with the tank. We also noticed that the temperature seemed to vary considerably for the first couple of minutes while taking a shower. After several adjustments at the tap, it would stabilize.
The next thing we noticed was the cold water temperature surges. This occurred at the sink during my morning routine. I would run the water till hot, do what I needed, then turn off the tap. If I needed hot water again, say to wash my face, I would turn the taps on, adjust the temperature, and begin washing. Suddenly the water would turn ice cold! That would last for a good 10-15 seconds before it became warm again.
This happens due to the way these heaters work. When they detect motion of the water, the heaters turns on. It can’t heat up the water instantly, so it takes 10 seconds or so before the water going through the heater actually becomes hot. This is why many people report that it takes longer for hot water to reach the tap. But, if you stop the flow of hot water for more than a few seconds, the heater shuts down. When you start using the tap again, the heater again takes 10 seconds to get hot. During that 10 seconds, a slug of ice-cold water is going through the tank and into your pipes. When it reaches your tap, the water goes cold, really cold!
While this effect is most noticeable in an on-off situation, it also occurs to a lesser degree in a flow or temperature adjustment. When you’re taking a shower, if you change the temperature or flow rate of either tap, it changes the flow rate through the heater. The heater takes about 10 seconds to catch up, so the water going through it is the wrong temperature during that time. This water reaches your tap, you notice the temperature change, and you adjust again. This is why we noticed the temperature “instability” during the first couple of minutes of a shower.
Note that all this is just while using a single water source. The effects get worse if you are using more than one shower at the same time, someone flushes a toilet, etc.
One last thing about the hot water supply. My teeth are sensitive to cold so, when brushing, I like to run a tiny stream of hot water to take the edge off the winter water temperature. Can’t do it with this heater. The flow rate has to be above a certain amount or the heater shuts down.
Cost Savings
Here’s where it gets a little murky. If you use your water in exactly the same way as you did with the old tank, you will probably save money. The number is not large, and I’ve read that it’s about 10-20%. However, due to the hot water supply issues mentioned above, I have changed the way I use hot water. When I start the tap at the sink in the morning, I now leave the hot water running till I’m done with everything, so it will stay hot. Due to the temperature variations at the start of a shower, I spend more time fiddling with the taps, and my shower now takes longer. And, since it takes longer for hot water to reach the tap, I’m using more water. Am I saving money? I doubt it.
Initial Cost
One of the selling points for this was that it would last much longer than the 10 year life of a tank, although I couldn’t get a real estimate of its lifetime. But, at three times the installed cost, this unit will have to last me 30 years just to break even. Do you have any appliance in your house that is 30 years old? Even furnaces are usually replaced every 20 years or so.
Maintenance
I have taken apart and repaired hot water tanks. They are dead simple - a tank, a heating element, and a thermostat. My tankless unit is anything but simple. There are circuit boards, digital controls and readouts, and moving parts such as variable valves. This is not something I can maintain myself. This means if something goes wrong, I’ll need an expensive repair call, with complicated, expensive repair parts. And then there’s the 30-year life I need to recoup my investment. Will there be parts available for my unit in 30 years? Even 20 years?
So, what are they good for?
I think they are NOT good for a normal family in a whole-house situation. If you are a family that currently has a small tank and you run out of hot water frequently, you’re better off just getting a larger tank.
If you have one or more small tankless heaters located very close to the usage point, many of the temperature problems will not be as much of an issue. If you’re single and don’t have to deal with others using water at the same time, that will help. Probably the best use for these is in occasional use situations where a regular tank would spend most of its time wasting energy to keep the water hot. Examples of this would be a single person who travels a lot on business, or a cabin or cottage that is only used on weekends.
Bottom line
If I had to do it over again, there’s no question. I would get a tank unit.
Recommended:
No
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dkuchta5
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