Electric water heater questions

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Post by dacflyer » Mon Dec 11, 2006 4:32 pm

i forgot to tell this..
i bought me a WH 2 yrs ago,, i bought the one with extra thick insulation,, its got a 3" surrounding. when its hot, i can turn it off and have HW for about 2 days..i have a timer on it right now, that cuts it off every 12 hrs,,and if i want it on, then i have to manually turn it on..i can tell the savings..
also the HW heater came with 4500 watt elements.. i changed them right away to 5500 watt elements...i too like long hot showers...and i have yet to ever run out..
any local plumbing place carries the hotter elements..and its safe to use..
just uses a bit more power.. try that,, its cheapest way to go before you commit to any thing else

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Post by richfloe » Mon Dec 11, 2006 5:00 pm

Low flow showerheads would help, I'm sure. I don't know how high my daughter has the flow but this is a new shower installed about 5 years ago by a plumber, it probably has the flow restrictor. The other shower that my wife uses is fed by the old-style hot and cold knobs, normally opened about 1/4 turn for a moderate flow, doubt there is the restrictor but any less water would be unacceptable. The big problem is the temp, they both want it hot.

Several years ago I had thought about the pre-heating idea but most of the smaller units were only a few KW and wouldn't help as much as I need it to (I would need a boost of 5kw or better). I also recall seeing either a warning against using one of the smaller heating units as a preheater (it was intended as point-of-use) or against feeding heated water into the water heater. A single unit is a better solution but if I could find a compatible water heater and pre-heater this might be a possibility but I would have to wonder why they would make it a two-piece system, they could just put it all into one package with the preheater built right into the inlet pipe.

I saw the 9.5kw instant electric heater, with the temp rise vs flow it would appear to barely make a tolerable shower. Water out of the ground is going to be about 55degF (if memory serves), at 1.5gpm flow rate the temp rise would get that to almost 100degF with the faucet set to full hot, barely hot enough and too low on the flow rate at only 1.5gpm. 9.5kw is not enough for a continuous shower. Of course at 9.5kw it will probably explode and kill a lot of people. I was only planning on going to 9kw with my water heater. 8) I can see that if something did go wrong, I could be in deep...

The water recirculating systems are great for large buildings or long runs but not necessary in my application. I had thought that if I had the room to put in a storage tank somewhere that a recirculating pump would be handy for that.

The on-demand units that I had seen for supplying a house ranged from a little over 100,000btu to over 200,000btu. The smaller said it would handle a shower, dishwasher, washing machine etc but one at a time. The larger units said they would handle two, possibly 3 things at once. Looking at the btu input (which is 3 to 6 times the input of a gas-fired storage water heater) shows just how much power it takes to heat-on-demand in a continuous flow application. I had figured that if I had 20kw that I might keep up with continuous flow of a shower but this just seems ridiculous somehow.

Again, yes, I did the math. I don't have the numbers with me but I worked it from a couple angles, this was the best:
I got literature on various gas and electric water heaters. As required by federal law, they have to tell you how much it will cost to operate the water heater for a year based on a typical family. The comparisons are the same, just with a different heat source. It said (just making up numbers here because I dont have them with me) that it was going to cost me $250/year for gas and $400/year for electric. This seems right, doesn't it, everyone knows heating with gas is cheaper. Here is where it falls apart. It also said that this is based on electricity cost of 0.086/kwhr and 0.97/therm. I wish. My cost per therm is about $2.30 after I factor in the customer charge ($13.50/month) and the delivery charge (Gas is sold here a little different that 'normal', I can choose what gas company I want to get my gas from and then pay the local gas company to deliver it to my house), as I said, tired of gas company ripping me off. As for the electric, the Highest I have ever paid was 0.075/kwhr and in the winter (using my heat-pump and resistive) my usage goes up which causes the price to drop, down to about 0.035/kwhr. Apply my higher than normal cost for gas to what they thought gas would cost and I end up with a yearly gas cost of $592 and a cost to do it with electricity of (figuring 0.065/kwhr avg) $302, gee which do I pick? These numbers are just off the top of my head but you get the idea.


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Chris Smith
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Post by Chris Smith » Mon Dec 11, 2006 6:34 pm

You do have to consider many things, like just the shower times VS hot water all day long.

The pre heater will cost you more in usage time during the shower, then shut off for the rest of the day,...while the electric heater will do its “lower cost jobâ€

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Post by Colinr » Tue Dec 12, 2006 5:18 am

why not adjust the thermostat on the HW tank a few degrees higher
when the showers are taken to get tha same temp the hot water will be mixed with more cold water to get the correct tempreture thus the fixed capacity of the HW tank will last longer.

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Post by Chris Smith » Tue Dec 12, 2006 8:38 am

Time set adjustable thermometers are better, other wise you waste lots of energy during the part of the day when no water is being used.

Storing such hot water all day is a loss as shown by many of the clips relating to conservation.

A preset timer before the shower time[s] is an alternative, and they are for sale last time I looked decades ago.

But that was decades ago, and things have changed.

Dean Huster
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Post by Dean Huster » Wed Dec 13, 2006 5:40 pm

1) The circulating hot water systems are nice, but hard on the plumbing. That constantly-running water truly will erode the pipes. That's info right from the plumber's lips and even though replacing the lines is potential income for them, they don't recommend the circulating systems unless they're really needed.

2) If you're getting 15 minutes of use it's because you're taking very efficient "Navy" showers. Even using "Navy" shower techniques as our family always does (we've had our fifth-wheel TT for 18 years now), it's easy to drain that water heater. Doing the dishes usually ends up with tepid rinse water with a bigger batch of dishes.

3) Around here, Missouri Natural Gas is high enough that some folks are getting $250 and $300 gas bills during the winter.

4) Adding a water heater insulating package to the outside of the tank is one of the biggest energy savers you can cheaply do. There's not much insulation between the tank and the outside cover of the original heater.

5) Upper elements rarely open because it's the lower elements that end up being buried in all the sand and calcium at the bottom, insulating them and causing them to burn out. The upper thermostat is an SPDT switch where the upper element has priority; if it's not "on", then the lower element is allowed to turn on if its thermostat is closed. An open upper element shouldn't make for a cold tank -- just a slow tank.

Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).


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Post by jollyrgr » Thu Dec 14, 2006 7:16 pm

Colinr wrote:why not adjust the thermostat on the HW tank a few degrees higher
when the showers are taken to get tha same temp the hot water will be mixed with more cold water to get the correct tempreture thus the fixed capacity of the HW tank will last longer.
While this is indeed will provide more hot water it is a very bad idea. All new showers do have antiscald valves in them but many existing ones do not. As of 1990 these were not required by my local building codes. By 1998 apparently they were. (This appears to be true in much of Northern IL and I don't think you can even buy a shower valve without antiscald protection.) I am not aware of sinks having antiscald protection.

My brother's water heater was turned up high. I noted when rinsing dishes at his house one evening that the water was quite hot and warned him so as well as the potential for a scald accident. His comment was that the very hot water "got the dishes real clean". This past fall I was there to clean and inspect his furnace. While in the basement we noted that the pressure relief valve on the heater had opened and was draining very hot water onto the floor. This water did not last long as it was so hot it evaporated rather quickly. I checked and noted that the temperature was above normal and adjusted accordingly. Still there is hot water but the relief valve no longer opens.

This thread intrigued me and I started researching "electric showers" and found many references in the UK, Australia, and NZ. But I also found shower heads with electric heaters on them made for RVs in the USA. These showers screw in place of the normal shower head pipe coming out of the wall. A heater about the size of a pop can is on top of the neck and has a normal 120VAC plug on it. Maybe you could use something like this to aid in your showers. (MUST USE GFI PROTECTED OUTLET!!!) The way this heats, according to the instructions I read, is based on the speed of the water. The faster the water, the lower the Delta T. Thus with already warm water you can get moderate pressure and lots of hot water. In other words what would be a luke warm shower without the device could be relatively hot with. Thus less hot water removed from the tank.

I've linked the image of one such device below.

No trees were harmed in the creation of this message. But billions of electrons, photons, and electromagnetic waves were terribly inconvenienced!

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Post by ian » Mon Dec 25, 2006 10:48 am

I've often thought about this kind of thing myself......

Electric water tanks are 100% efficient as opposed to gas because ALL of the heat is transferred to the water. Most people think gas is always cheaper and this is a cheap trick the gas companies play on. The fact is an electric tank is much better.

But the fact is, modifying the tank IS illegal.

What about using another tank as a warmer? Suppose you got another tank and installed it BEFORE your hot water tank. To be "safe" you could only warm the water to a few degrees above room temp. Possibly power the two coils in SERIES with 110V? Even if the thermostat failed the water would never heat up much past room temp.

To be COMPLETELY LEGAL AND SAFE........what if you installed a tank before the heater tank and stripped all the insulation out of it and didn't hook it up electrically? The water in that tank would warm to room temp and feed your heater tank with lukewarm water. This WOULD be safe AND legal.

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