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Domestic Water Heater Question
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Sleepster Offline
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Post: #1
Domestic Water Heater Question
I have a modest 1300 sq ft single-story home. Water supply enters the building at the south end, and currently we have a conventional tank water heater at the north end of the building. We have to wait a long time to get hot water in the bathroom located at the south end of the building, so I installed a circulator pump atop the hot water heater. The circulator kit comes with a valve that I installed under the sink in the bathroom at the south end. And there's a timer. This works ok, but I think the valve is failing as we seem to have more hot water in the cold lines than we used to. Plus I think our water heater is near the end of its life.

I'm thinking of eliminating the circulator pump kit and installing a small tankless heater to serve the south bathroom, locating it in the attic just above that bathroom. It's a small unit. Google "3.0 GPM Indoor Natural Gas Powered Tankless Water Heater Model #i12-NG" from Home Depot.

Is this unit large enough to serve that bathroom? It has a sink and a shower. I don't want to encounter any performance issues at that shower as it's the one that my wife uses and ... well, it's the one she uses!

Can I connect this tankless unit in a "parallel" configuration?

Later, can I simply replace the tank heater with a tankless unit? Probably one larger as it serves both the second bathroom, the kitchen, and the laundry room; which are all located at or near the north end of the building.

It seem to me that having two heaters connected in parallel at opposite ends of the house will improve performance throughout the house as hot water can be drawn from both heaters at the same time, but I have a feeling I may be overlooking something important.

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02-15-2016 01:14 AM
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AlanE Offline

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Post: #2
RE: Domestic Water Heater Question
The way to determine if the system is adequate is to add up the flow rate of all the fixtures. You may never run the faucet and shower at the same time but this is how you figure your GPM. Faucet is say .50-.75 and shower, if it is a low flow, around 2.6 would give you about 3.1 - 3.2 GPM flow rate.

Second thing you need to do is calculate your temp rise. How much above cold water temp you need to raise. If you assume 50 degrees f for a cold water temp and you want the typical temperature of 105 degrees f at the shower you need a system that can produce a 55 degree f rise in temp and flow at least 3.1 gallons per minute.

According to the description, that unit you mentioned does a 35-40 degree f rise at a flow rate of 4 GPM and a 77 degree f rise at 1.5 GPM. 50 degree at 3 GPM should be obtainable. It's max rating is 4.8 GPM.

The closer you can mount it to the bathroom the better and obviously it needs to be vented and it needs 110v power. Code will determine where you can mount it. If applicable. Here, we can't mount it in the attic and we have to pull a permit. Though these installs are hard to regulate and enforce. YMMV.

As for parallel as long as you are not feeding the hot water back into the hot line you can have as many demand heaters tapping off the 'hot' line as you have water pressure to support. (demand heaters can't be pre-heated.)

Replacing the north end will be expensive. That will need to be a larger unit. With the addition of the demand heater at the south end you could install a smaller tank at the north end. Say 35-40 gallons. Just a thought.



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02-15-2016 08:46 AM
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Crimson Nape Offline

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Post: #3
RE: Domestic Water Heater Question
Three of my friends have upgraded to tankless gas water heaters. Each had to go back and install larger gas supply lines, with one having to increase the supply line to the home. I realize that this isn't your question but I wanted to throw it out here for your consideration.

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02-15-2016 09:22 AM
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Sleeprider Offline
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Post: #4
RE: Domestic Water Heater Question
I'm in a house twice that size at 2700 square feet in a single story with a full finished basement (5400 sf total). The 50 gallon gas, power-vent water heater is located centrally near the furnace. This distributes water reasonably quickly throughout the house.

In relocating a second unit, you will have a lot of costs including the second tank as well as gas, flue (or electric) services and the connections to the cold and hot water lines. I would carefully consider relocating the hot water to a single central location, which will still involve gas, electric, flue, tank and connections. The power vent exhausts through a PVC pipe, which is relatively inexpensive (the water heater with vent is not). That makes it possible to locate the tank away from a conventional chimney. Still, I would avoid dual hot water heaters in a house of that size.

The tankless water heater is tempting, but remember installation costs will still be high to run gas, power, plumbing and venting. A centrally located water heater is a pretty easy modification if you have a basement. Sounds like you might be on a slab.

One last note, you mentioned having hot water in the cold lines. That would get pretty expensive. A HW circulation system should have a back-flow valve installed anywhere a hot/cold connection is possible, and hot water pipes must be well insulated.

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02-15-2016 09:35 AM
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surferdude2 Offline

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Post: #5
RE: Domestic Water Heater Question
Consider using your existing pump and installing a dedicated return line in the attic back to the water heater cold inlet. A 3/8 o.d. soft copper will be sufficient. I did that on my last home and it worked very well. Depending on how cold it gets in your attic, you may need to run the pump continuously during very cold weather. Insulation alone will not fully protect against freezing. Even so, I recommend insulating the line to reduce heat loss and make the system more efficient. I used Armaflex but the foam type is cheaper and just as good.

Dude

edit: You will want to include a check valve in the return line to prevent backflow of cold water under certain demand conditions. It's not absolutely necessary but desirable.
(This post was last modified: 02-15-2016 12:24 PM by surferdude2.)
02-15-2016 11:19 AM
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justMongo Offline

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Post: #6
RE: Domestic Water Heater Question
It's a tankless job; but somebody's got to do it.

INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
02-15-2016 11:38 AM
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Homerec130 Offline

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Post: #7
RE: Domestic Water Heater Question
We looked at going with a central tankless heater and the maid show stopper was we would need to upgrade our gas line from the street to the house to a commercial vs residential line. (From what we were told the difference is in diameter). Between the cost of the new line and the associated permits on top of the heater, it was not cost effective to do it. It would still be cheaper to put a traditional heater when normalizing the costs over the life span of the heater.

Our 1900 sq ft house was built in 2000 and our hot water heater is in the garage on the side closest to the master bath. Getting hot water to the master is good, but it takes a while to get it to the other bathroom and kitchen as they are on the far side of the house.

I am still running the original heater and in the process of looking at replacements. Don't dare drain it as the sediment may clog the valve.

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02-15-2016 12:05 PM
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SuperSleeper Offline

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Post: #8
RE: Domestic Water Heater Question
(02-15-2016 11:38 AM)justMongo Wrote:  It's a tankless job; but somebody's got to do it.

Chortle, chortle... Too-funny

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02-15-2016 12:40 PM
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pholynyk Offline

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Post: #9
RE: Domestic Water Heater Question
I was hoping we would all ignore that.
02-15-2016 03:41 PM
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surferdude2 Offline

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Post: #10
RE: Domestic Water Heater Question
Now you're gonna get into hot water pholynyk Nervous
02-15-2016 04:18 PM
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