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How good are instant electric hot water heaters–new construction?
My wife dislikes reduced flow shower heads and she takes long showers and likes the water to be a bit above 105 degrees. The incoming water is from a well and will be about 55 degrees.
Will instant electric hot water heaters produce enough hot water for her?
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What do you think? Electric? Should be obvious. What's the GPM rating on the heater?
*Here's the calc: gpm x temp rise x 146 = wattsThe 146 has units of min x watts/gallons/degreesF which is just the heat capacity of water in different units.So 3 gpm x 50F temp rise x 146 = 21,900 watts for a nice flowing, indefinitely long shower. Half that if she's willing to take a low-flow, 1.5 gpm shower. So look for a 20kw+ unit or two 10kw+ units plumbed in series.How good are they? I've been very annoyed with ones that I've used in Europe. The heat output didn't adjust with flow, it was either on (when flow exceeded a low set point) or off. So if you turned the cold faucet up, the shower got colder (of course). But if you turn the hot faucet up, the shower also got colder (because the wattage is fixed but you're increased the flow). To get it hotter, you turn off all the cold water and DECREASE the hot water flow. Until you get down to that low-flow shut-off. Then it all gets very cold.I listed other options for having lots of hot water under the thread, "High-efficiency boiler worth the $$$?" in the "Energy: Heating, Insulating, & Venting a House" topic. For a continuous shower from an 80% efficient gas heater(s), you need about 90,000 BTU/hour. -David
*Hoo! Hoo! I just love it -- picturing a 21,900 watt demand water heater in my house. 91 amps @ 240 volts. I think the spouse would have to undergo a change in behavior, were she mine. There's an old saying I read once about country plumbing, and one thing it said was that it don't take city habits.
*Yeah, that electric meter sure would spin fast ($2 to $3/hour). Consider how little the 4500 to 7000 watt element can do in an normal electric water heater once it's out of hot water. That's why it has a 40 gallon tank. Need light, computations, or horsepower - use electrons. Need heat? Burn something (LPG, NG, oil, wood, coal, junk mail, whatever) - it's always cheaper.Just had a bright, cheap idea. Run another 30 amp circuit to your (presumably) electric hot water heater and wire the bottom element to pull power whenever it wants instead of being secondary to the upper element. Also check the upper element and upsize the element (and the wires and breaker!) to 7000 watt (hard to find, about $35). Two 7000 watt elements would give 2 gpm continous. Or 3 gpm for about 30 minutes if starting with 40 gallons already hot.
*David,Are you assuming something like a 2:1 tempering ratio of cold to hot? Flyfisher's spouse likes 105 degrees, so she may require a little more hot water to start, or maybe he can boost the tank to 180 degrees or so. Plays hell with washing the dishes, though.
*I didn't factor in the extra heat of a really hot water heater - although that's always one way to make a 40-gallon HWH act like a 70-gallon HWH. Install a tempering valve and crank the HWH thermostat. I've got one HWH under my kitchen set at 120F - great for doing dishes by hand and the dishwasher will boost to 140F automatically. Plus there's the instant hot dispenser for a quick cup of tea. And another HWH under the bathroom set to 130F - the better for topping off the tub to keep it hot during an extended soak. Like when a new FHB arrives. -David
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Dear David, Barry & all readers: You guys know some stuff! You're right, it takes about 91,000btu
@ 80% eff' to do this. Our RA28 (28kw) model is 99.3% efficient, & will run a 105deg/3gpm shower all day long, assuming you have a 200amp service. Because it is classified as a variable load: It may be installed in virtually all new homes, and any existing homes with a 200amp service. The RA22 is for buildings with 150amp service. Yes they will spin the meter, but ONLY while being used. Overall, your electric bill will go DOWN, because it only comes on when you want it to. I supply these units, as well as gas & propane units. I have a patented showerhead, rated at 2.25gpm max @ 80psi, which will satisfy ANYONE, or I'll give you your money back. Contact me at 1-800 851 9891, and I'll get info to you. Or e-mail me. [email protected]. Cheers Brian.
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How good are instant electric hot water heaters--new construction?
My wife dislikes reduced flow shower heads and she takes long showers and likes the water to be a bit above 105 degrees. The incoming water is from a well and will be about 55 degrees.
Will instant electric hot water heaters produce enough hot water for her?