I wanted to convert the domestic hot water to electric.
Some goals of the project:
Less oil dependence
Nearly Instant hot water to all taps
Energy efficiency
Endless hot water at a very controlled temperature
Smart Controls and remote control via phone apps
Obtained a used eemax 23kW tankless and a 6 gallon hot water heater.
Got a whole mess of ¾” PEX and brass connection / valves etc..
(See parts list below)
Remove all existing ½” hot water copper lines.
Install a direct ¾” line from the meter to an Aqua pure descaling filter then an expansion tank.
Replace the aquapure filter every 6 months. Your hot water devices and faucets will thank you.
Pipe into a loop that circles around the basement joists underneath each tap.
Go through the joists safely or under them and secure with pipe fang straps.
Use barb connections wherever possible, they are way less expensive than shark-bites and will outlast them too.
Some connections will have to be shark-bites, just be smart with them.
Avoid soldering connections unless you are experienced, the quick clamps are just too easy.
Also, I suggest using the PEX as freezing issues all but go away.
They can expand to accommodate most freezes based on my experience with a house in NJ that has exposed pipes.
Install a shut off valve and tee at each tap.
Install the tankless water heater as close as possible to your electrical panel to reduce costly 6GA wire requirements.
Immediately after the tankless, pipe the outfeed of the instant into the 6 gallon tank.
Install a shelf for your 6 Gallon water heater and hang it from the rafters. (I put mine near the kitchen sink as that gets the most usage.)
I removed the old 6 gallon water heater heating element and the pressure release valve as they were shot.
I also added a webstone cold water bypass valve isolator to drain the tank when needed – as my tank had no drain valve.
Replace the heating element with a 1500 watt unit so you can use a 15 amp circuit. (though I installed a 20 amp circuit with 12GA wire to keep the wire resistance less)
Using a 15 amp load also enables you to utilize a WEMO switch!
I adjusted the temp to 122F on the 6 gallon tank.
Insulate all the PEX pipe with foam or rubber, as you are not looking to heat the air. Leave no surface behind, try to get the valves too, be creative. I use the PEX cutters to trim the pipe insulation.
Install a stainless steel recirc pump at last part of the loop just prior to the infeed – choosing non stainless steel is a bad choice and will cause things to rust. Don’t do it.
Install a Honeywell aquastat and set it to around 85 degrees and the hysteresis dial to 5 degrees – you can find these used too. Don’t get the clip on aquastats, they stink and you can’t fine tune your system.
Mount the aquastat on a 12” long section of copper ¾” pipe, as the PEX does not transmit the water temp well due to its low specific heat. Your aquastat will be close to useless if mounted on PEX pipe unless you want to waste energy.
I have the recirc pump controlled by a WEMO switch and in series with the aquastat.
Make sure to include a check valve so there is no back flush of cold water to your taps!
Not currently used but:
I also ran a bypass in/outfeed run off the main loop back to the oil burner domestic coil to have redundant systems, or for possible winter applications.
I also ran one more in/outfeed run off the main loop to a 50 gallon water heater. This can be used in the winter to “store” water at a warmer temperature then the ground water from outside. Additionally, DC heating elements could be added to preheat the water prior to entry into the main hot water loop. Thus far I have not used it yet, but will update in the future.
Set the 23 kw Instant hot to around 125 degrees – will take some trial and error.
BTW you will need (2) double pole 50 amp breakers for this guy. It uses a lot of juice when on full demand, but if you figure you are only using it for an hour per day or so, depending on household size… it really is not bad. Use a union prior so you can remove and clean when needed. I also mounted mine on a sheet of plywood and put some rubber cushion to serve as a noise mitigation device. As when the contactors are energized, they click a bit. Mine is in the basement so can’t hear that much but good to be safe.
Set the WEMO switches such that they turn on the 6 gallon water heater at 6:15am, then the recirc pump at about 6:45 to 7am. This will ensure that you have instant hot water at 7 am in time to wash our face, shower, or what ever…
I do the same timer sequence at 445pm so that we are ready to make dinner and wash hands by 515
If you find yourself taking a shower at a similar time, add some more timers etc… you will minimize the length of time it takes to get hot water.
Though I will tell you that even from a dead cold, the tankless 23kW will heat up the whole loop(including the 6 gallon tank) in 2-3minutes. So essentially activating the recirc just prior to going in the shower works fine. And yes, you can shower until your body prunes into oblivion, the hot water never runs out!
The system without the 6 gallon tank is not pleasant to use. It gets too hot and has longer lag times. The 6 gallon tank serves as a mixing chamber and provides a 2-3 minute buffer of hot water. The temp stays rock steady at 122 which is perfect for showering, laundry, handwashing, and dishwasher.
Make sure all your faucet pressure balance valves are working properly(the diaphragm commonly breaks over time), or have separate taps for Hot and Cold. You will have hotter water with separate taps and can likely turn the temperatures down vs having all your water mixed. But with a hotter setting, more people can use hot water devices simultaneously.
You can leave the recirc on for whenever you are in the house so that it satisfies the aquastat temperature, but we don’t use much hot water during most of the day since at work/school so no sense in heating water.
Additionally, I have a WEMO rule such that if my phone is not in the geofence of my house block area, it turns off the WEMO switches.
Integrate to your IFTTT app – google for more info.
Technology is pretty wonderful.
One should note, that even without the recirc system on(nor the 6 gallon heater element on for that matter), the hot water from the tankless punches through the 6 gallon unheated/circulated tank quickly. Mainly impart due to the fact that hot water rises over top of cold water. You could also install the tankless electric after the 6 gallon water tank, but i'd rather have the preheated 6 gallon tank last - My theory (though untested) is that it provides a steadier output temperature during the first minute or two of hot water demand (handwashing) which is frequent in a family of 4 household. Thus lessening the chance of getting scalded. I would also imagine that if you triggered the 6 gallon to heat several times per day and had the tankless after, you might consume less electricity overall - but lose some output temp conformity... especially for short cycle uses.
An alternate system would be to have instant water heaters at every tap, but with 7 hot water taps in the house: kitchen, 2 bath sinks, 1 tub, 1 shower, washing machine, basement sink…. It seems like it might be an electrical and cost challenge. But eliminates a lot plumbing in the house by doing away with hot water lines.
One note: When using the oil boiler domestic coil, I always found the water temp to fluctuate from super hot to lukewarm plus it seemed that a lot of energy went up the chimney. With an electric system, very little energy is wasted and it has a high efficiency – though your price per kW may make it more expensive. If you have your own solar PV system, electric is def the way you want to lean. Also note that natural gas is not available on our street… so that will have to weigh into your heating method decision matrix.