Electric tankless on-demand water heater basics

[wpcoe]

I'm renovating a home in Mexico (I will be splitting my time 50/50 between Thailand/Mexico once it's finished) and want to install an on-demand "multi-point" electric water heater.  In Thailand these are fairly common and I've had them in my past four Thailand homes.  However, I've been stuck in Mexico for three years and have trouble remembering what type of heater I even have in my Jomtien condo.

 

Tankless on-demand electric heaters are relatively new here.  Most people use a gas heater, usually with a big tank.  None of the "changs" that I'm working with have ever seen one, and even the experienced contractor I'm using has never used nor installed one, so local knowledge is pretty slim.

 

Seems like the entry-level heaters are 110v and 3.5kW, with a few 110v 4.5kW units.  There are a fair amount of 220v models starting at 5.5kW.

 

The climate where I am is almost identical to that of the Pattaya area.  Rooftop water tanks are ubiquitous here, too.  There are tons of scathing reviews for almost all of these heaters on Amazon, even for a 220v 7kW unit, saying they barely warm the water.  I have my suspicions that these reviews are from folks who live in colder climates, but not sure.

 

Is a 220v 5.5kW heater adequate for a one-bedroom home (think condo) for sinks & shower?  What do you think about a 110v 3.5kW heater?

[KhunBENQ]

Do you have 220 V supply in Mexico?

110 V, 4 5 kW is roughly 40 A!

You must have serious cabling there.

Is the electricity net (state monopoly?) generally reliable and able to  supply the needed power?

 

We have a 4.5 kW, 220 V here and with the fairly cool temperatures it's fighting to get warm water not to say hot.

Do you have morning temperatures of 14 C?

With "Pattaya climate" I would assume 4.5 kW is good enough for a normal shower head.

If you need it turbo strong massage shower maybe not.

 

 

[sometimewoodworker]

5 hours ago, wpcoe said:

The climate where I am is almost identical to that of the Pattaya area.  Rooftop water tanks are ubiquitous here, too.  There are tons of scathing reviews for almost all of these heaters on Amazon, even for a 220v 7kW unit, saying they barely warm the water.  I have my suspicions that these reviews are from folks who live in colder climates, but not sure.

 

Is a 220v 5.5kW heater adequate for a one-bedroom home (think condo) for sinks & shower?  What do you think about a 110v 3.5kW heater?

The best information will come if you can check the actual supply water temperature. If you can site your supply tank on the roof and you have decent sunshine you can get by with smaller unit.

 

However even if you are managing to get 30 degree water supply from the tank a 3.5kW heater is only going to give warm water showers. A 5.5 kW heater is going to give you hot showers with that kind of input temperature, but the colder the supply water temperature is, the greater the power that you need. We have 6 kW units and when the supply temperature drops to under 20 degrees we can’t get hot showers.

[Encid]

On 1/21/2023 at 4:47 PM, sometimewoodworker said:

We have 6 kW units and when the supply temperature drops to under 20 degrees we can’t get hot showers.

At our house in Najomtien (near Pattaya) we have an underground water tank, so the water temperature is always cool... even chilly in the cool season.

 

We installed 8kW Redring water heaters (from the UK) 15 years ago and have never had a problem getting piping hot water whenever we want.

We mounted them under the bathroom sink so both the shower and the sink have a hot water supply (essential for shaving).

 

When the weather gets warmer and the ambient temperature of the water in the tank rises, we turn down the heaters for a couple of months so we can enjoy cool showers.

Sure they use a bit of power when you want a nice hot shower, but it's worth it.

 

I will be installing similar in our new build up-country soon.

 

 

[wpcoe]

Most of the 110/120v heaters here are 3.5kW, but yeah, 4.5kW would need hefty cabling.  Electrical supply is as stable as in Thailand.  We have 14°C mornings as often as Pattaya, i.e. not often.  (I don't think we went that low this winter.  Yet, anyway.) 

 

From the comments here, I think what I probably have in my Jomtien condo is a 3.5kW heater.  When I was in smaller homes and in a low-rise smaller condo building with rooftop tanks, in the summer the "cold" water was warm enough for a shower without turning the hot water knob.  In a high-rise condo, the cold water's not quite that hot, and in the winter whatever heater I have (3.5kW?) is enough for hot, but not scalding, shower.

 

I think there's a big difference between underground tanks and rooftop ones exposed to the sun, and the latter is what I have in Mexico.

 

After reading these comments, I think I'll go with a 3.5kW or 4.5kW 220/240v heater.  Thanks!