Hot or cold water for initial tub fill?

[Ohiotubbin]

Hello again. Still waiting for my caldera Marino to be delivered.  I was thinking about when I fill the tub I have an electric tankless water heater that lets me set the exact temperature of my hot water in the house. We usually keep it at 117 degrees. The thing is super energy efficient, so my thought was instead of using cold ground water (northeast Ohio is usually in 40-50 range) I set my on-demand water heater to 102 and fill from my washer hot water spicket. Am I overlooking any reasons why this wouldn’t be a good idea? I figure I can save some money on the first heating too.

Also, since I am on well water with a softener, are there any specific concerns with the initial water chemistry I should be aware of? I am going to ask the dealer when they deliver to test the water and give me a specific instruction on this, but general knowledge is always appreciated.

[wmccall]

Hi neighbor, state wide at least. I assume you are in NE Ohio.   This question gets asked a lot, but in my 15 years here, I think this is the first time anyone with one of the tank less heaters has asked.  Have you ever tried to get 300-400 gallons of hot water at once?

[Ohiotubbin]

I can’t say that I have, though in theory it should be an unlimited supply.  I don’t know if that long of a constant run of the heater would stress it too much or not.  How long does a fill take? 2 hours or so?

[Spatech_tuo]

I can’t say that I have, though in theory it should be an unlimited supply.  I don’t know if that long of a constant run of the heater would stress it too much or not.  How long does a fill take? 2 hours or so?

It all come down to: what do you gain? Nothing that I see really.

[Tman122]

I can’t say that I have, though in theory it should be an unlimited supply.  I don’t know if that long of a constant run of the heater would stress it too much or not.  How long does a fill take? 2 hours or so?

It all come down to: what do you gain? Nothing that I see really.

The only thing you gain is the ability to go in sooner. They both cost about the same to heat.

[gmdodt]

My manual says specifically not to fill with hot water as it can mess up sensors

[Spatech_tuo]

My manual says specifically not to fill with hot water as it can mess up sensors

The only way I'd consider this is as a supplement to the regular fill method so the starting temp was higher and furthermore I'd only do that if it were the dead of winter.