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Joined: Jan 2005
Posts: 5,445
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Cat Servant
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I suppose we need to get ready to see more point-of-use heaters. The method does have it's advantages.

In "traditional" construction, all the things that used hot water were placed close to each other, and the heater was nearby as well. For example, in a recent building I worked on, the kitchen counter was on the opposite side of the bathroom wall, with the heater placed in the basement directly beneath.

Yet, today homes are not laid out that way. Bedrooms are scattered about, each with it's own bath. The kitchen is often pretty distant from the garage - a common place for the heater. Yesterday's job was in such a home, where the kitchen was the room farthest from the garage.

In such designs, the small size of these heaters, the easier piping, and the lack of delay waiting for the hot water to reach the faucet make them attractive options.

I would not be a bit surprised if someone starts selling "water heater cable" ... a relative of Romex, with 6-#8's and 3-#12's in it. That, naturally, will lead to countless discussions here about de-rating issues laugh

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Joined: Jul 2007
Posts: 1,335
S
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Fuel oil contain 138,000 btu's per gallon. One kilowatt of electricity contains just under 4000 btu's. My on demand oil fired waterheater burns just over a gallon an hour and 88% efficient so it utilizes about 122,000 btu's per gallon. Electric heat is 100% efficient so you need about 30kWh of power with an equivalent heating equipment.


"Live Awesome!" - Kevin Carosa
Joined: Mar 2005
Posts: 1,213
S
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Oh, believe me, I understand the physics involved. But the requirement remains to get those BTUs into the water as fast as it's used, which requires a fat pipe, beit electrical or gas.

Some energy savings are realized over a conventional hot water heater in that there is no thermal loss through the hot water tank insulation. In practice, though, I think these losses are overstated- yes, a hot water heater uses a lot of electricity, but that's because it's heating up a lot of water. I think I worked it out once to around 25-50 cents per shower. Of course, I was taking a shower at the time I worked it out, so those numbers might be a bit off wink

Joined: Oct 2006
Posts: 745
E
Member
Romex with 6 #8's and 3 #12's............Now that's funny!
I can't even begin to fathom how much that would cost per foot, not to mention the weight!

Please forgive my ignorance here as I never did well in school with math. So if I understand:

(using local east coast prices)

30KW of electricity costs about $2.10 for an hour.
One gallon of fuel oil costs about $3.75 for that same hour.

The net BTUs produced are roughly the same. I know that oil and gas prices are insane right now, but with nearly a 80% difference, why would there even be an option here?


---Ed---

"But the guy at Home Depot said it would work."
Joined: Jun 2004
Posts: 1,273
T
Member
The story is the waste of energy while the hot water is maintained 'at idle'.

Plainly, energy is lost every moment of the day from the hot water system. That's no problem if you're on solar power. Otherwise, the bulk of your energy consumption tends to be for the heat lost while NO WATER IS FLOWING. Tankless gains its merit from that fact.

If three phase power were available, then a single three pole C/B at 208Y120 could power up the three elements when wired delta.

Aiming at the residential market this high power insta-hot stacks three single phase 240V elements into one device.

I pity the poor installer who has to get (6) #8 conductors through a 3/4" KO. My advice: open it up to 1".

As for getting the field wiring in place start thinking of 1" PVC in the underslab/ or 3/4" ENT/SMURF tube (Flex?) with pre-installed conductors in the overhead.

Either way, quite a bump up in effort for the electrician.




Tesla
Joined: Jul 2002
Posts: 680
W
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Joined: Jul 2002
Posts: 8,443
Likes: 3
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Originally Posted by renosteinke
I suppose we need to get ready to see more point-of-use heaters. The method does have it's advantages.

In "traditional" construction, all the things that used hot water were placed close to each other, and the heater was nearby as well. For example, in a recent building I worked on, the kitchen counter was on the opposite side of the bathroom wall, with the heater placed in the basement directly beneath.

Yet, today homes are not laid out that way. Bedrooms are scattered about, each with it's own bath. The kitchen is often pretty distant from the garage - a common place for the heater. Yesterday's job was in such a home, where the kitchen was the room farthest from the garage.

John,
Do houses in the US no longer have a Laundry room?
Over here, this room is often the most central room of the house (in a single level construction).
Often the hot water cylinder would be installed in there with lagged pipes run to the various plumbing appliances.
I have also seen them installed in roof spaces, but that's a whole thread in itself.

Joined: Jan 2005
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Cat Servant
Member
Yes, we still have "laundry rooms." though 'out west' there is a tendency to place the laundry equipment in the garage.

The challenge is that we no longer have any location "central" to the water use, and the distances the pipes run has grown quite a bit over the years.

For example, yesterday's job was a house whose floor plan sort of resembled the letter "F." Bedrooms were in the base of the "F," and the top left part. The kitchen was the top right. The garage the middle "bar." It's almost as if they wanted things to be as far apart as possible.

Another common design these days is the "O", or courtyard design. In this arrangement, one side is a massive garage (imagine it at 6:00) most bedrooms would be at 11:00, with a guest suite at 3:00, and the kitchen/ laundry at 7:00.

Kind of makes you miss the traditional ranch style home.

Joined: Oct 2006
Posts: 745
E
Member
Sounds like as much of a horror show for electricians as it is obviously for the plumbers. That makes our traditional colonial construction around here with basements sound a lot better than I thought. We don't have any equipment in garages here, but then again, we have basements for the HWH, HVAC and laundry facilities. I will admit that my laundry room is on the second floor which is a lot more handy.


---Ed---

"But the guy at Home Depot said it would work."
Joined: Jul 2004
Posts: 9,923
Likes: 32
G
Member
Basements are called "indoor swimming pools" in Florida and second stories tend to be called "wind borne debris". Long, low ranchers are the norm. (although we do see piling houses at the beach and some 2 story McMansions) The architects usually put the laundry on the opposite end of the house from the master bedroom so you have a lot of pipe between them.
I do think that if you just had 20-30 gallons of storage in the attic you would have all the hot water you need most of the year here for free.


Greg Fretwell
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