The BIG tankless water heater post
Thursday, November 29th, 2007If you’ve read our blog before, you know that we have had some ups and downs with our tankless water heater. You can read about our noise problems in this post, and our joy in receiving a replacement unit from Bosch here. The long and short of the story is that I rebuilt the supply gas line twice, trying to resolve a problem that turned out to be a defective gas valve in the heater. Given the massive number of comments we received on those posts and the numerous questions I’ve gotten from friends, I’ve been wanting to put together a new post that shares our opinion on the pros and cons of tankless water heaters. Also, I’m going to share our overcomplicated but effective plumbing layout. First, I’ll start with a picture of our Bosch 635ES (aka 250SX) in all its glory:
Tankless Heaters – why use them?
I think most are familiar with tankless heaters, but just in case you’re not, I’ll touch on this topic. There are several reasons to consider using a tankless heater:
- Energy conservation – since a tankless heater heats water only when needed, they use less energy than tank heaters. Although tank heater insulation has gotten much better over the years, a heater that doesn’t have any standby heat losses will always be more efficient. Also, I would argue that since a tankless can be set at a lower temperature (since you don’t have to jack up the temp as you might with a tank in order to extend your supply), there will be slightly less heat lost through your pipes and insulation to the surrounding air due to the lower temperature differential. Our heater is set at 110° vs the 120-240° most people set for the tank heaters.
- Endless hot water – as long as your tankless is large enough to meet your needs, it can supply infinite hot water. This is great when you’ve got visitors staying at your house, and the fifth shower is the same temp as the first.
- Smaller footprint – being able to hang the heater on the wall saves a lot of floor space. Ours sits above our washing machine, so it’s not taking up any valuable space.
- Direct venting – many of the gas tankless heaters support direct venting out the side of the house. This was a big plus for us, since we were removing our old chimney to gain extra space in our kitchen. An electric tankless wouldn’t require any venting at all, but I’ve not read too many good things about them.
- Longetivity – since tankless heaters are mostly made of copper tubing, as opposed to steel tanks, they will not rust through and should outlast tank heaters by a wide margin.
Why not use a tankless?
Although opinions will differ widely on this topic, you probably already know if you are a tankless person or not. Some people, like us, get so committed to the idea that we kept at it until we had a system that worked for us. Others don’t want any hassle or to spend more money than they have to, so I wouldn’t recommend them if that describes you. I often compare them to hybrid cars. You buy one because you want to use the least amount of energy possible, not because you think you may even out the extra cost with lower gas usage. While the payback of a tankless really isn’t all that bad once you factor in rebates and tax credits (see below), I think the inconveniences would scare off someone who wasn’t really motivated to save energy just for the principle of doing it. And don’t think that there weren’t many times during our troubles that I came very close to ripping ours out and plunking down a big ‘ol tank. There were moments where I didn’t care how much we had invested in it…it just wasn’t worth it. Imagine how I felt after upgrading to 1 1/4″ gas line because our gas run was a tiny bit longer than Bosch recommended for 1″ line (to which I had upgraded from 3/4″), only to find that we still had noise problems, since the unit was defective. I don’t believe that our situation was the norm, though, so please don’t take our initial bad experience as a deterrent. However, there are a few tankless traits that make them not suitable for everyone or their homes:
- Intermittent/low-flow issues – this is my least favorite trait of tankless heaters. While they excel at providing unlimited showers, they pretty much suck at the little stuff, like washing hands and doing dishes. Imagine someone washing their hands in the bathroom when the water in the pipe is totally cold. It may take 1 or 2 extra seconds for the hot water to reach the sink (compared to a tank), since the heater has to kick on once it senses the flow, but that person will not even know that you have a tankless heater. But now imagine that a second person goes in to wash their hands. At first things will be fine, because the line is already full of hot water from the previous use. But there will be some cold water introduced into the line due to the startup delay, and if they wash long enough that cold blast will make it to the sink. And that will be followed a couple of seconds later by the “new” hot water. And all tankless heaters need a minimum flow rate to even turn on, so too low of a low will always come out cold. We learned new behaviors, such as filling a sink for dishwashing or shaving, instead of using little bits at a time. But eventually we got tired of having to think so much about “gaming” the system that we eventually added a mini-tank heater under the kitchen sink. That worked out so great that we installed another one to serve the bathrooms a year later. You can read about our hybrid system below.
- Gas line size – if your gas line (from the meter to your heater) is too small, the heater will not be able to run at full output. If you don’t meet the manufacturer’s recommendations, you may have to upgrade at least part of your line. That’s not a big deal if you can do it yourself, but imagine it could get pretty spendy if you’re paying a plumber. Our unit is one of the higher capacity units, and its 160,000 BTU capacity dwarfs the 80,000 BTUs of our furnace. A tank heater doesn’t really care about the gas supply, since it’s heating a large amount of water at a slower rate. Of course, that’s also why they run low on hot water after a shower or two has depleted the tank. They just can’t recover quickly enough to keep up with lots of showers.
- Expense – there’s no escaping the fact that tankless heaters cost 2-3x as much as tank models, but there are many federal and state tax credits and rebates available to help offset the cost. The direct vent models also usually require some fairly expensive stainless pipe, which can add $100-200.
Our funky but effective hybrid system
As mentioned above, we eventually grew dissatisfied with having to always out-think the heater when it came to lower flow or intermittent uses. Eventually, we added in two mini-tank heaters to solve this issue, as well as minimize water wastage, since we now have true “instant” hot water at most of our sinks. Although they are reducing the efficiency of our hot water system somewhat, they seem very well insulated. It does mean that some of our heating now comes from electricity, which costs more than gas, but it is definitely nice to waste less water. And if you’re curious about the energy usage, I used my Kill-a-Watt meter to average out their consumption. The 4 gallon heater uses 25 watts, and the 6 gallon uses 37. These are averaged out over several days, so they suck this energy down around the clock. Although it might be slightly more or less depending on your usage, in our case it’s like having a 60 watt bulb running 24/7. I’d rather not be doing that, but some amount of that is offset by water that does not have to be heated by the tankless anymore. And just as important, we don’t ever have to run more water through a faucet than we actually need, since we don’t have to get enough flow to force the big heater to activate.
We have a 4 gallon Ariston under the kitchen sink and a 6 gallon in the basement that feeds the basement bathroom sink, the main bathroom sink just above as well as Chloe’s sink upstairs. It will also feed our (future) bar sink in the basement. In retrospect, we might have used a 6 gallon for the kitchen sink, because it does sometimes run out if we have to handwash a bunch of pans while running the dishwasher. But even when it does, it’s inline with the tankless heater just below, so it’s easy to “recharge” it quickly. Here are pictures of the heaters, as well as a diagram of our expensive and overcomplicated, yet effective hot water system. This is not for the faint of heart or cheap or wallet, and while we are very happy with it now, I can’t honestly say whether we would have gone this route knowing what all lay ahead.
