I’m an electrician. I haven’t been impressed by most of the tankless systems I’ve hooked up. I would definitely go with gas unless you are willing to run some serious power. Most hot water tanks pull about 3000-4500W or 12.5-18.75A at 240V. A good tankless system is upwards of 18000W or 75A at 240V and some can be around 36000W which works out to 150A. This will easily be the single largest electrical load in your house, unless you also have an electric furnace or something. Depending the size of your electrical service and what else you have in your house you may need to upgrade the electrical service going to your house as well. Most Residential Electrical services are usually 100-200A in my area.
I mean I know things are different here in Europe but 18kW for a water heater? Why? I have one that plugs into a regular outlet, so no more than 3.5kW, and I have no issues whatsoever. Sure, water isn’t boiling hot out of the tap, but I can take showers no problem and usually need to mix a little cold water to make it comfortable. Why would you need any hotter water? Or is there some other reason why you need so much more power in an american system?
The 3.5 kW heater will have a tank reservoir that will have time to heat up the water when it’s not being used. Tankless means it has to be heated instantly.
So if a shower uses, say, 9 litres per minute, i.e. 0.15 litres per second, heating that water from 10°C (typical cold water temperature) to 40°C (comfortable shower temperature) is:
4 • 0.15 • 30 = 18 kW
Anything less heats less water per second, or to a lower temperature.
Like this 5.1 l/min unit at 9.5 kW will be able to heat that flowrate ~28°C above its inlet temperature.
I’m an electrician. I haven’t been impressed by most of the tankless systems I’ve hooked up. I would definitely go with gas unless you are willing to run some serious power. Most hot water tanks pull about 3000-4500W or 12.5-18.75A at 240V. A good tankless system is upwards of 18000W or 75A at 240V and some can be around 36000W which works out to 150A. This will easily be the single largest electrical load in your house, unless you also have an electric furnace or something. Depending the size of your electrical service and what else you have in your house you may need to upgrade the electrical service going to your house as well. Most Residential Electrical services are usually 100-200A in my area.
I mean I know things are different here in Europe but 18kW for a water heater? Why? I have one that plugs into a regular outlet, so no more than 3.5kW, and I have no issues whatsoever. Sure, water isn’t boiling hot out of the tap, but I can take showers no problem and usually need to mix a little cold water to make it comfortable. Why would you need any hotter water? Or is there some other reason why you need so much more power in an american system?
The 3.5 kW heater will have a tank reservoir that will have time to heat up the water when it’s not being used. Tankless means it has to be heated instantly.
It takes ~ 4 kJ to heat 1 kg of water for each 1°C. If you want to do that in 1 second, you need 4 kW of heating power.
So if a shower uses, say, 9 litres per minute, i.e. 0.15 litres per second, heating that water from 10°C (typical cold water temperature) to 40°C (comfortable shower temperature) is:
Anything less heats less water per second, or to a lower temperature.
Like this 5.1 l/min unit at 9.5 kW will be able to heat that flowrate ~28°C above its inlet temperature.
Oops, my bad, I really thought it used a regular 240v plug. Turns out its hooked into my kitchen’s high voltage (400v) circuit and uses 21kW.
Thanks for explaining why physically my assumption could not be possible.
Good lord, well that puts that into perspective, thanks.