Can I use this unit inline to give me instant hot water until the hot water makes its way from the tank heater on the other side of the house?
This unit requires 220 volts on a separate circuit with its own Ground Fault Interruptor circuit. It has a low flow rate and would typically only be used for one sink or other device. Its rare to have 220 volts on a dedicated circuit at a sink location, so it doesn’t appear to be a practical option for most.
And although they pitch the energy savings compared to a tank water heater, if you have a gas fired water heater its hard for me to believe that using 220 volts to heat water for one sink is going to save significant $$$ or energy.
I’d like to see a serious tankless water heater capable of providing water to multiple outlets on Woot.
So… due to the flow rate this may not even be good for a shower?
I have no idea if these particular tankless water heaters are good or crap, but I’m curious if anyone has considered this idea:
I live in an apartment building (a condominium) and it can take a good 90-120 seconds for hot water to arrive at my sinks.
I’m considering putting a tankless water heater under my sinks on the existing hot water line, and set to a few degrees cooler than the building’s hot water. My thinking is that the tankless heater will give me hot water quickly, and then switch off, using little or no power, once the building’s hot water reaches it.
I realize that these require a separate 220V circuit. For my bathroom, this is fairly trivial because the main breaker panel is less than five feet from bathroom and I can do the wiring myself, though I would likely hire someone to do the plumbing (I hate plumbing).
Also, I’m aware that hot water is included in my monthly common charges, while electricity is not. I do realize that this idea will cost me more than I am currently paying.
Here is the manual FWIW
Okay, I’ll try to give you what little I know about these tankless heaters. I assume this one is like the one I put into my greenhouse 10 years ago. That one cost me around $300. It died 2 years ago. I haven’t had it fixed and I think it might be time for me to purchase one of these instead!
I used it for watering orchids. In winter, the water out of the pipes here is extremely cold. This served my purpose by raising the water temperature a bit. The water passes through it, and as it does, it gets heated. The faster you run your water, the cooler the water temperature is. That is my experience. You could adjust the temperature a bit, but it wasn’t highly adjustable.
I think that’s what the chart is trying to tell us - you need a more powerful unit the colder your incoming water is.
Semi-quickly written, unqualified talk only:
I’m not completely sure, but I think these woot units are only flow switch activated. If the flow rate is sufficient (usually higher than in units that can modulate), the unit turns on at a fixed setting (full on, fixed temperature rise). There is no temperature monitoring with electrical output modulation on these units. So when your building’s hot water hits, it will be heated too with near the same temperature rise as when the water was cold, hopefully only until some thermal cutoff safety trips in the tankless.
They do make modulating electrical units. Ecosmart and Stiebel Eltron (Tempra) both should still be. The concern then I have is how reactive the units are (depends on flow, how much rise, wattage of the tankless, how many heat elements in the tankless, how good the temperature detection and modulation is). Usually when a tank and a tankless are inline, they’re close to one another and deal with slower temperature transitions (as the tank turns cold from use, the tankless would provide boost to maintain temperature). Yours is a 2 minute cold/room temperature slug then the hot water hits.
As to solutions…depends on your situation. How much spare amps do you have on your panel? Do you have space for a tank anywhere and if so, what size? Budget? Gallon per minute of the hot water pipe full blast?
Solutions, for example–
Without knowing the tech, my guess is that if you only had space for a pure tankless solution, a somewhat oversized (for heat output needed) unit that uses many amp breakers of smaller size and was physically/dimensions larger would be more reactive.
On the other end but similar, you could simply buy a small tanked water heater, acts like a buffer tank, the larger the better. Depends on your gallons per minute, but 10 gallon might do.
A mix of the previous 2 would work too (5 gallon tank, smaller modulating tankless).
Another solution is to use a hot water recirculating pump on your incoming lines to the apartment. Probably the simplest solution. You cross/tie the hot and cold lines upstream (just after they enter your condo) and that has a pump in the middle that is thermostat controlled to run when the hot water line drops. However, there are a LOT of caveats with that, one especially is the plumbing lines (you are pumping into the common cold line) you are dealing with are not yours alone, which is a huge issue and pretty much disqualifies this as a real option imo.
I would consider having your condo association install a recirculating pump. They’re inexpensive and relatively simply to install. Even if the installation is complex for some reason (no good return line options) running a new line, even in a large building, wouldn’t be more than $1000.
The cost savings are instant. Not only do you waste less water, but you use less energy heating water every time someone uses it. If you are in a building where heated water is built into the assessments, everyone will save money.
This is more expensive but is a product built precisely for your issue.
I was thinking of getting one of these since our kitchen is the furthest spot from the Water heater but procrastinated since we hardly use heated water there.
 someone upstream mentions that this sort of solution pumps it back through a common line and I didn’t consider this since I live in a condo that doesn’t share plumbing.
In looking at the specs I am a bit confused by the listing of 35/45/77 degree * RINSE*… should that say RISE ??
(and should the last column be 75 not 77…?)
My powers of deduction are not the best, especially this early in the morning, but I think the 6.5 and 8 kw unit prices are reversed.
** FIRE HAZARD WARNING !!**
Also, in looking at your technical table in the picture to the right of the listing, there is an error in the wire size for the 13kW unit AT900-13. According to the information in the manual (re-posted below), it requires a #4 AWG field wire (the ground line can be a #8 AWG).
Depends on your incoming water temp. US flow rate for shower heads is 2.5 gal or less by design. So if your incoming water temp is 55degrees the AT900-13 would give you about 2 1/4 gal/minute of 100 degree water… and as already mentioned, lower flow rate =higher temp gain, so if you were running 2 gallons a minute it would be higher than 100
Making water hot: It’s a tankless job.
There are pumps you can buy that keep the hot water circulating and reduce the wait time.
As noted by MRLN a few posts back…
Here are a couple answers from the vendor:
> In looking at the specs I am a bit confused by the listing of 35/45/77 degree RINSE… should that sayRISE ??
(and should the last column be 75 not 77…?)
Correct, this should be RISE, not Rinse.
No, should be 77 F (not 75 F)
> My powers of deduction are not the best, especially this early in the morning, but I think the 6.5 and 8 kw unit prices are reversed.
This is correct, because it is a typo. Should read 3.8kW, not 8kW.
> Also, in looking at your technical table in the picture to the right of the listing, there is an error in the wire size for the 13kW unit AT900-13. According to the information in the manual (re-posted below), it requires a #4 AWG field wire (the ground line can be a #8 AWG).
*The image was never changed to the attached image I sent over with the correct information, stating #4 AWG. *
No way. Well, a Navy shower maybe, but a good (Rheem) whole house tankless water heater will run you close to a grand. Installation costs could run you more than that. These things generate tremendous amount of heat, and they must be vented to the outside with a certified, dedicated vent system. I thought about it, but someone told me it might cost me $1500 or more to install. Looking at a good, high efficiency standard tank type now.
You’re pricing sounds about right, and let me say it’s worth every penny! We installed a Rheem about 10 years ago and never looked back. Imagine endless hot showers for multiple people while doing laundry and dishes.
The best part, you can go up to the unit an instantly turn off the hot water to the house if someone is lingering in the shower too long! (not that I would EVER do that…)