HOWTO: Install a Tankless Hot Water Heater
Unlimited Hot Water
When I bought my latest house I was already planning on some upgrades to various things. One of these was the hot water heater. The water heater that came with the house was old and would start to run rust-colored water if the faucet was left on long enough. I'd been hearing about the new "tankless" style heaters so I went gathering information about them. Turns out they did what I wanted, using much less energy in their off state since they only heat water as it flows, there are no large reservoir tanks to worry about keeping warmed.
I installed my heater after finding rust and silt in the bath tub when trying to take a bath. I performed a second installation with a friend after she saw how nice the tankless heater worked, and her hot water heater just plain stopped. This article is the result of the lessons learned during both of those installations.
When I went looking for information on installing a tankless hot water heater most places told me simply to find a "qualified professional" and have them do it. Well, I'm a do-it-yourselfer so that wouldn't cut it. I found very little information on installing a tankless heater, thus this guide was born. The following items are the things I wish someone had told me ahead of time.
- Sizing: From what I have found, you determine which tankless hot water heater you will buy simply by deciding how many active faucets you want to be able to use at one time (each instance of you using hot water is known as an "application". So a 2-application water heater would be good for, say, running the shower and the dishwasher at the same time.) Since I am able to plan my days well enough and I have a smaller house with only two people in it, I figured a single application tankless would fit my needs. This also cut the cost of the heater in half, and brought it to within a close range of comparable tank models. The heater I ended up with (based on local availability) was the Bosch Aquastar 125B from Lowes. Home Depot did stock the Aquastar 250B (a two-application model at twice the price) at one of their stores, but they couldn't confirm stock. Since I already had a natural gas heater in the basement, I naturally went with the natural gas version. There are also LP (liquid propane) and electric models available from the various tankless hot water heater manufacturers.
- Placement: A normal tank hot water heater sits in the middle of the floor. A tankless model hangs on the wall (by two small hooks). This makes a huge difference in the amount of space you need, but it also means you need an open part of the wall to hang it from. My heater isn't particularly big at 30"H x 18"W x 10"D (with the cover on), but if you have a hot water heater stacked in a closet with a furnace you may not have available space to hang it. It is also light enough for one person to unpack and hang by themselves. My tankless heater (and I believe most others) is rated to hang on a finished wall, but I placed it on a couple of horizontal pieces of 2x4 against the cinder-block basement wall so I really had no concerns about excess heat. The heater I purchased also included a handy paper template I could tack on the wall to determine height and spacing.
- Plumbing (Water): If you decide to do this yourself you
will likely need to relocate your water pipes. Since most hot water heaters sit
in the middle of the floor the cold and hot lines are pre-run to the inlet and
outlet of the tank. I ended up cutting a small section of my existing pipes off
and running the new pipes back to the wall then down to the bottom of the
tankless heater (the location of the new heater's inlet and outlet pipes.) To
do this I just purchased a couple of 90 degree elbows and a few sticks of
copper pipe. The pre-soldered elbows make this job a lot easier to do,
especially if you will be soldering your new pipes up against a finished wall.
- Plumbing (Fuel): My hot water heaters use natural gas
(while yours may use electricity or liquid propane.) As such the feed pipe for
the existing heater needed to be extended to the new mounting point on the
wall. This was accomplished by changing the horizontal run of "black pipe" from
6" to 24". I could have re-routed the pipe along the ceiling and dropped it
closer but I was trying to make it as simple as possible (and having a vertical
pipe didn't impact the amount of room the heater was using much, it's right
next to my boiler in the utility room anyway.) One thing to keep in mind if you
are using natural gas is that the kit should include a gas regulator that mounts
vertically. So before mounting your new tankless heater on the wall put the
regulator on the gas inlet and try to hang the heater high enough that you only
need to change your existing horizontal run. I learned that lesson the hard way
and the second installation went much smoother for it.
- Exhaust: By far the biggest trouble I had was doing the exhaust on the new tankless hot water heater. Basically the old heater had 3" ducting and the new one required 5" ducting (or 6" ducting at high altitude, which Denver qualifies as). The existing 3" duct needed to be removed, which was easy enough, but finding the right duct work and getting it shoe-horned into the existing exhaust was not easy. My boiler sits right next to the hot water heater and I was finally able to find a Y pipe that would let me splice in the new exhaust piping. A friend has also heard you need double-walled ducting for the entire system, though I only used double-walled into the existing ductwork. I may upgrade later, but for now it seems to be working well. On the second installation I performed we mounted the heater directly under the existing duct, so the only upgrade that was needed was a straight piece of double-walled exhaust ducting.
- Missing Brass: One thing I did find annoying was that in the kit
there was a purge valve (useful for draining the heater), but all of the brass components
required to get the valve installed were not included in the box. In the photo below you will see what I
ended up purchasing, the parts include:
- 3-way adaptor.
- (2) brass reducers between the 3-way and the outlet threads (shown as the steel-braided cable.) The outlet is 1/2" and the brass 3-way had a 3/4" inlet. My copper piping was also 3/4", so I needed a second reducer on the left side to get the threads to the right size.
- Male-Male 3/4" pipe adaptor. This was due to my poor planning. If I'd been thinking ahead I would have soldered a male end on the pipe you see on the left of the photo.
- Garden hose adaptor. This sits on the drain side of the purge valve, letting me attach a hose to it so I can drain out the trap in the floor of the basement, rather than letting the water just run all over.
- Time: Keep in mind while you are doing this that you will not have hot water in your house (and if you don't have a separate shut-off valve for the hot water heater you will need to turn your mains off so you may not have running water at all.) Budget enough time for this. It took me about 5 hours on a Saturday for my first install (partially due to having to run to Home Depot and Lowes a couple times), the second install was about 3.5 hours.
I am very pleased with my home upgrade to a tankless hot water heater. As you can see in the photos below the space savings were enormous. My utility bill (for natural gas) has dropped by almost a third. I can shower for as long as I want without ever worrying about running out of hot water (or getting rust and sediments out of it.) Another advantage is that the service life on this tankless hot water heater is 20 years. Most of the new hot water heaters I looked at charge a big premium to have a service life of even 12 years, so I will be enjoying my trouble-free hot water for even longer. The installation was challenging, mostly due to my lack of advance knowledge and planning, but it certainly is within the reach of a competent DIY'er. After reading this you have any questions or comments, go ahead and contact me and I will do my best to answer them.
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