The Water Heater

** Update 6/19/2007 ***

I was just asked how much, if any, noise the water heater makes and realized that I hadn’t mentioned this practical tid-bit.

“Noise” is a relative term – as any parent arguing with a teen about music selections will know – but by my definition it’s anything that stands out from the native environment.

For the tankless water heater there are two sources of noise, neither of which I find objectionable, but both are new/different from what you experience with a conventional tank water heater.

First is the sound of the selenoid(s) adjusting the water flow to assure a consistent temperature. You can hear them doing their thing as a distinct muted hum. This is very brief and is usually only when the unit first comes on when it’s trying to get the water up to the initial operating temprature. This would be on par with the sound of the burner starting in a conventional heater.

Second, the exhaust fan. I mention below that it will run for a minute or so after the unit turns off and it runs the entire time the unit is in use. This is somewhat louder than the sound of a conventional unit’s burner operation. Again, not objectionally so but you will hear it. I think I can safely say it’s about as loud as a common bathroom exhaust fan.

** end Update **

As I mentioned in my earlier post on our renovation plan, we elected to invest in a tankless water heater, not so much for the fuel economy – our gas bill for heating water was never terrible – but rather for the promise of infinite quantities of hot water. Our new bathtub will be able to hold up to 74 gallons. It would be a real shame if/when we decided to take advantage of that we ran out of hot water.

Moving the heater back to the center of the house where it would be at the originally intended beginning of the household hot water plumbing means that all the faucets should receive hot water as quickly as possible. Being on a slab we don’t have a lot of inexpensive options for re-routing the plumbing so it wasn’t really practical to consider leaving the heater in the laundry room and trying to re-route the pipes.

We ended up with a Rinnai R85i unit which, practically, I think we can expect to achieve about a 6.5 gallon per minute (gpm) flow rate (for a 50 degree farenheit temperature rise).

The technology for this tank is amazing. It uses a double walled vent (chimney in our case) where the middle section is used for exhaust and the gap between the two walls is used to draw in fresh air. This serves the double purpose of cooling the exhaust as well as ensuring that you are not drawing on your internal, household air for combustion. This prevents the possibility of Carbon Monoxide gas being drawn into the home should a vacuum condition exist (maybe you’re using your fireplace or you’ve got exhaust fans or are similarly actively venting air out of your house). So your home interior is never exposed to the flame or gas.

When you set a temperature, so far I’ve tried 125 degrees and 130 degrees, the unit will make sure that the water exiting is at that temperature. A low flow, such as from a sink faucet, will cause only some of the burners to activate while a greater flow, such as a shower or tub, will cause more burners to activate and burn at a higher rate. There is also a valve on the outgoing pipe so if the water is not being completely heated because it’s flowing through too fast, it will choke down and reduce the flow. This can translate to lower pressure at the faucets, but everybody using the water will have consistent heat. Combined with a Thermo-balance faucet (which we are installing in the master bathroom shower) this should ensure that you have a consistent temperature no matter what happens.

Given that a generous shower flow is rated at about 2.5 gpm we should easily have enough capacity for a couple of showers and a sink or two before any choking is required. I imagine two people taking a bath at one time might be a challenge, but the worst that can happen there is that both tubs will take a little longer to fill. Since you won’t run out of hot water, I don’t really see that as a problem.

2270Here is the closet (top half anyway) before we did anything to it. Note the valves that were already in there from when the original heater was moved to the laundry room.

2272Here we have the shelf and drywall removed. That yellow hose is the gas line. These tankless water heaters don’t use as much gas as a regular tank but when they use gas, they need a lot of it. They don’t have the luxury of spending an hour or so heating a tank of water, the water needs to be up to the desired temperature in the time it takes to pass through the unit. We needed a 3/4 inch feed which we fortunately had easily accessible in the attic.



2250Here the unit is mostly installed. Even though I was aware of the measurements beforehand it is still much more compact than I was picturing it to be.


2258And here we have the last part of the old piping removed (note that the valves are gone) and the condensate pump is installed. That’s the little white over black box to the right. The double-walled vent can be prone to condensation forming and if you have a greater than 5 foot rise (ours is going almost straight out the roof) then you need to have a collector and a way to get rid of the condensation that forms. It’s kind of like a tiny sump pump for the heater. We’re pumping the condensate back up to the attic and then over and out to the old hole in the wall that the water tank used for the pressure-relief pipe.


Still left to do is to dress up the pipes and the wall with some sheetrock to make it a little more attractive. I’ll post a picture when that piece is done.

The door to that closet is a louvered door (all those little slats) . It was like that to allow the original water heater unrestricted air flow. That is not necessary with this technology and there is an active fan that runs for a minute or two after the unit has finished burning to clear any remaining exhaust away. It’s not that loud but I think a solid door would make sense now to completely muffle the sound.

I was very excited when we got this installed and played with almost every faucet in the house. I say “almost” because everybody forgot to check the clothes washing machine. It turns out that this was not hooked into the original plumbing, but rather was hooked directly into the pipes feeding our old hot water tank. Inside the walls where nobody could see. What a surprise when we tried to wash some clothes and got absolutely no water! Ah well, we’re trying to determine whether or not there are any pipes left behind from an original setup for the washing machine or if perhaps it was located in this room concomitantly with the original hot water tank relocation.

I’m rather hoping that we can find the pipes and that this hookup was done to get the hot water to the washing machine as fast as possible. It would be quite the round trip for the hot water otherwise. The washing machine would be mostly full before the water would even begin to warm up, having to travel to the middle of the house and then back again if the original piping was used.

For reference (I couldn’t find the original reference page that I used) check out this article to get an idea of the water consumption of various items in your home.

Installing this technology is still a relatively expensive proposition. The cost of the venting pipe is very high as its construction is pretty sophisticated and it’s not very common. You can expect to pay 3-4 times for the actual heater unit as you would for a tank plus you’ll almost definitely have to pay extra in labor to replace your existing vent. In my case I had to pay yet more to relocate and replumb stuff. I think it’s not implausible that my actual break even point vs. just installing a hot water tank will be in about 8 or 9 years. But the absolute dollars are only part of the real equation…


4 thoughts on “The Water Heater”

  1. The best solution to the problem (if one should arise) of two taking a bath at the same time would be to use one tub…..I always say the first thing that comes to mind. Anyway, have you solved the washing machine pipe or pipless dilema? For me, just having a tankless water heating system is quite something.

  2. Two sharing a bath is certainly an idea. I think the issue is probably more hypothetical than anything else. With the new soaker tub there’ll be plenty of room. We may have to invite folks over so everyone can share! 🙂

    Right now we have a garden hose hooked up to the washing machine until we can craft a more permanent solution. We’re still trying to find the original owners to simplify the pipe-finding process. If worse comes to worse we’ll probably run some copper pipes through the attic parallel to the now-obsolete plastic pipes that used to feed the water heater. Apparently those were subject to bursting – everybody who saw them warned about them. I don’t want to reuse them, though it would probably be WAY more cost effective in the short term…

  3. A tankless water heater also known as point of use water heater or on demand units, turns on when you open a hot water faucet and turns off when you close the faucet, so the energy that is consumed is only for the hot water that is being used.

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