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Old 04-12-2012, 11:45 AM   #1
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Considering Tankless HWH... Reality Check Please!


I currently have an older gas heater that I feel is poorly installed in a less-than-ideal location. Its gurgling every time it fills make me think that I may not have a whole lot of time left on it, so we're starting planning to replace it.

We're thinking about relocating the HWH and going with a tankless to:
  • Reduce gas bill
  • Reduce time to get hot water
  • Reduce water bill
  • Ensure reliability

Also of note:
  • Current HWH is poorly wrapped
  • Current venting looks to be out-of-code
  • None of the pipes are wrapped at all
  • We'll be opening the kitchen walls for a reno
  • Current installation is on slab-on-grade (garage conversion to living space), rest of house is on footings

The current installation:



The current layout (3 bd / 1 ba):



X = Current HWH (manuf. 1997 / 40 gal / 32k BTU / " line / 3" vent)
X = Proposed tankless HWH (hall closet)
O = Kitchen sink, bathroom sink, shower
O = Planned dishwasher

For scale reference, the distance from the present HWH to the kitchen sink is 15' to 16' straight-line and the proposed closet location is 28" W x 33" D.

We like the idea of putting it in the hall closet because the piping for the shower is in that wall, because the closet is much too deep to utilize properly for storage, and we'd like to get the space back in the laundry room.

Reality check please!
  • Is there enough space in this closet to meet installation requirements and code?
  • Could we legally run track-style removable wire shelving in the front half of the closet, or is there an approach clearance requirement?
  • Is running the plumbing and gas lines feasible for a carpenter and a DIYer after a reading a few books and with plenty of patience? (no experience running gas or plumbing)
  • If we have to hire this out, is there anything we can do to "help" the pro to keep the costs down, like removing the drywall and cleaning up for them?

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Old 04-12-2012, 11:50 AM   #2
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Considering Tankless HWH... Reality Check Please!


Almost forgot...

House is located in the Central Valley of Northern California. Do not have water data on hand (yet) from City, but think it's slightly hard. Relatively few days of frost per year, and only snow once in a blue moon.

Quote:
Each winter, on average, your risk of frost is from December 9 through January 25.

Almost certainly, however, you will receive frost from January 2 through December 22.

You are almost guaranteed that you will not get frost from February 26 through November 16.

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Old 04-12-2012, 12:49 PM   #3
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Considering Tankless HWH... Reality Check Please!


Quote:
We're thinking about relocating the HWH and going with a tankless to:
Reduce gas bill
Doubtful as most modern Energy Star tanked units don't run all that much. Ours got flooded out and 2 days later I was still drawing warm water (not hot but not cold) from the tank.

The total BTU needed to heat water is not going to change. IE; you will still need the same amount of BTUs to heat the same amount of water.

Quote:
Reduce time to get hot water
Friends with one say it takes them longer to get hot water. Think about it, the tank has to sense water usage, fire up, warm up the line and the heat exchanger and then put out hot water.

Quote:
Reduce water bill
Not sure how a hot water heater will help with that.

Quote:
Ensure reliability
Some would say there are more points for failure in a tankless.

We looked at it when we replaced ours. Not worth it when I could walk into Home Depot and walk out with a $500, 50 Galon gas tank model that was a drop in replacement. Compared to the $1000+ of a tankless and the retrofitting. $500 buys a LOT of gas.
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Old 04-12-2012, 01:03 PM   #4
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Considering Tankless HWH... Reality Check Please!


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Originally Posted by itguy08 View Post
The total BTU needed to heat water is not going to change. IE; you will still need the same amount of BTUs to heat the same amount of water.
Entirely correct. However, the total BTU needed to hold the water at a constant temperature would drop to nearly 0.

Quote:
Originally Posted by itguy08 View Post
Friends with one say it takes them longer to get hot water. Think about it, the tank has to sense water usage, fire up, warm up the line and the heat exchanger and then put out hot water.
Interesting. Hadn't heard that. Will have to research that direction.

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Originally Posted by itguy08 View Post
Not sure how a hot water heater will help with that.
The idea was if I get hot water faster, I put less cold water down the drain. But this one hinges on the above assumption.

Quote:
Originally Posted by itguy08 View Post
Some would say there are more points for failure in a tankless.
Either there are more points for failure or there aren't, regardless of how many people say that there are. Unless you're an existentialist...

Quote:
Originally Posted by itguy08 View Post
We looked at it when we replaced ours. Not worth it when I could walk into Home Depot and walk out with a $500, 50 Galon gas tank model that was a drop in replacement. Compared to the $1000+ of a tankless and the retrofitting. $500 buys a LOT of gas.
Indeed, a lot of gas. Not sure I want a drop-in replacement, with that room being so poorly insulated that it may as well be considered outdoors. Then again, insulating a tank could negate much of that.
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Old 04-12-2012, 01:15 PM   #5
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Considering Tankless HWH... Reality Check Please!


Some things to consider assuming you mean tankless gas heater... Make sure to read the venting requirements in detail. If it is a high eff unit it may be impossible to run the required vent and intake pipes depending on install location you choose. At the very least running these pipes is likely to be difficult and expensive. Another major consideration is the sizing of the main gas line into the house. These units have big burners so it may have to be upsized to supply the necessary gas flow simultaneously to this WH and other existing gas appliances.

I looked at this in detail for my house a couple years ago and quickly decided it was not worth the hassle or expense. Your situation may vary depending on the details.
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Old 04-12-2012, 01:19 PM   #6
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Considering Tankless HWH... Reality Check Please!


I installed a gas tankless unit in my house, and would never go back to a tank model. There is no question that a tankless saves you money. But they do cost more.

One thing you should consider concerning where to put it is how to route the intake and exhaust. That can get expensive in a hurry. But there are units designed to be mounted outside, which would solve that problem.

I knew you were in CA as soon as I saw the picture - I've never seen water heater straps anywhere else. I was born in CA (Eureka) and grew up in Santa Rosa.

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Old 04-12-2012, 01:20 PM   #7
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Well, I have empty attic directly above, and the wall is non-load-bearing and non-insulated, so I figured it would be a shot straight up.

Is that a naive assumption?
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Old 04-12-2012, 01:23 PM   #8
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Considering Tankless HWH... Reality Check Please!


Go tankless and you'll love it....


Rinnai R98i is the real deal....


And as far as your plan to locate the unit in that closet, closer to the bathrooms? Yes!



Bottom line is that yes it does cost more on the front side, and yes, it will lower the monthly gas bill (although I understand that natural gas prices my soon drop rather drastically anyway. But still.).




Been there, done that...
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Old 04-12-2012, 02:45 PM   #9
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Considering Tankless HWH... Reality Check Please!


Quote:
Originally Posted by Thadius856 View Post
Entirely correct. However, the total BTU needed to hold the water at a constant temperature would drop to nearly 0.
Tankless heat exchangers are typically 15 to 20 % more efficient then hot water tanks. Additional overall efficiency is acheived becasue there is no standby loss.


Quote:
Originally Posted by Thadius856 View Post
Interesting. Hadn't heard that. Will have to research that direction.
How long it takes for warm water to arrive at a fixture is more dependent on the length and diameter of the pipe, and how well the pipe is insulated. In theory the hot water tank would provide warmer water quicker, just becasue there is a 130 degree heat source sitting at the end of the pipe versus a 50 to 70 degree cold tankless unit. But the effect is minimal. So most of your improvement will come from moving the heater closer to the fixtures.

Quote:
Originally Posted by Thadius856 View Post
Indeed, a lot of gas. Not sure I want a drop-in replacement, with that room being so poorly insulated that it may as well be considered outdoors. Then again, insulating a tank could negate much of that.
Most tankless units will be easier to vent then tanked units. Also, don't forget about combustion air supply. In the garage it had the entire garage for combustion air. If you hide it in a closet the closet will have to have vents to allow air in.

One thing that no one mentioned is the gas supply. You may have to upgrade the gas supply line to 1". We nixed going with tankless, becasue it required 1" supply and we only had 3/4" from the street. Because our water is so cold (mid to high 40's F) the plumber recommended 2 units in series or a solar preheater.
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Old 04-12-2012, 06:18 PM   #10
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Considering Tankless HWH... Reality Check Please!


Quote:
Originally Posted by goosebarry View Post
One thing that no one mentioned is the gas supply. You may have to upgrade the gas supply line to 1". We nixed going with tankless, becasue it required 1" supply and we only had 3/4" from the street. Because our water is so cold (mid to high 40's F) the plumber recommended 2 units in series or a solar preheater.
I called the utility company about this and they said that they have no information on what size line I have coming in. However, they did tell me that my meter is the "small" size they offer, which is capped at approximately 42,000 BTU. I haven't climbed the roof to check on the BTU rating for the central heat, but I'm not hopeful that I could get it all on this meter.

They said that they could *probably* upgrade my meter size *maybe for free*, but the lady on the phone was really unsure. She said she'd have to assign the case to a worker to come blah blah... something... blah. Either way, I'm less than 1,000 ft from a major gas pipeline. She said that *usually* service upgrades are done for free, but couldn't tell me what the largest gas line I could get here was either.
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Old 04-12-2012, 06:21 PM   #11
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Considering Tankless HWH... Reality Check Please!


http://www.consumerreports.org/cro/a...heaters-ov.htm
A little more info for you
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Old 04-12-2012, 07:36 PM   #12
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Saw the article from CR. I take all CR articles with a grain of salt. I've seen quite a few reviews where I question their accuracy (for example, Behr as the #1 paint brand).

Thanks though!
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Old 04-12-2012, 09:52 PM   #13
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Quote:
Originally Posted by goosebarry View Post
One thing that no one mentioned is the gas supply. You may have to upgrade the gas supply line to 1". We nixed going with tankless, becasue it required 1" supply and we only had 3/4" from the street. Because our water is so cold (mid to high 40's F) the plumber recommended 2 units in series or a solar preheater.

Good point about upgrading the gas line. However, I should point out that just because you needed to upgrade to 1" doesn't mean the OP would need to. He may very well need 1 1/4' or even 2", maybe 1/2" will do it. Who knows? Sizing a gas line isn't using whatever size pipe you saw on a similar appliance. There is a proper procedure using pressure, allowable pressure drop, longest run, demand, etc. One way to upgrade your supply without installing new piping is to get a higher delivery pressure from the meter (Such as 7" WC to 2 psig). This involves installing regulators, but it is often easier than re-piping.
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Old 04-12-2012, 09:53 PM   #14
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Considering Tankless HWH... Reality Check Please!


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Originally Posted by hvac benny View Post
Good point about upgrading the gas line. However, I should point out that just because you needed to upgrade to 1" doesn't mean the OP would need to. He may very well need 1 1/4' or even 2", maybe 1/2" will do it. Who knows? Sizing a gas line isn't using whatever size pipe you saw on a similar appliance. There is a proper procedure using pressure, allowable pressure drop, longest run, demand, etc. One way to upgrade your supply without installing new piping is to get a higher delivery pressure from the meter (Such as 7" WC to 2 psig). This involves installing regulators, but it is often easier than re-piping.
Hmmm. Greek to me. Lady on the phone said something about .25psi, I think. Does that mean anything intelligible?
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Old 04-12-2012, 10:00 PM   #15
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Considering Tankless HWH... Reality Check Please!


How about the dreaded cold water sandwich? Have you heard of that one?

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