My primary goal is making sure we have sufficient hot water to accommodate our big bathtub and our weekend guests, so that's just a matter of sizing for the most high demand scenarios.

Secondary goal is low cost to operate.

With the electric tankless, I'm concerned about cost to operate, but the math gets kind of fuzzy because obviously the hybrid tank gains efficiency due to the heat pump, but then also paying to keep the tank hot vs just using on demand resistance heat.

We are planning on 400 amp service already, and intend to add solar panels 2-3 years down the road. I need to review with the electrician because we'll be using a lot of electricity - 36" induction cooktop, double wall oven, boat lift, ice maker, heat pump HVAC, and electric water heater of some sort, and want capacity for a future EV charger.

For new construction on this size house, if we go tankless, would a single whole home heater, or zoned be better?

I was thinking if we go electric tankless, could do one in the upstairs laundry room, to feed the laundry, master bath and guest bath, then one in the ground level mechanical room, for the kitchen and main floor hall bath. This would also reduce lag time to getting hot water at the faucets.

Another option that might be appropriate is sdding a mixing/tempering valve to your water heater. The idea is to run your water hotter and ”temper” the outout with cold water to normal hot water temperature. The end result is that you have essentially increased the capacity of your water heater.

Here is an article:

https://www.rheem.com/water-heating/articles/how-a-mixing-valve-can-get-more-out-of-your-water-heater/

There are several caveats listed in the article, including including:

1. Running water heater at higher temperatures can cause it to fail sooner than at lower temprratures. How much sooner? The article doesn’t say.

2. Mixing/tempering valves fail slowly, allowing a hotter mix through. The article recommends monitoring output temperature regularly to catch failures early.

Maybe someone here has experience with mixing/tempering valves on water heaters and can comnent on whether they are a good idea or not.

Why would he do this? He's designing the system now- design it with the correct size.

Thanks Jake! I saw some comments of yours on old posts, which were mostly regarding questions from people looking to replace old electric tanks with an electric tankless, was hoping you would chime in here.

@stm25rs

Something for you to understand is that on an electric heater, the standby losses of a tank are minimal. It's a bit different for a gas tank water heater - because those have an open flue up the middle of them.

The reality is that tankless water heaters don't save energy because they are tankless... it's because the gas versions are generally about 93% efficient vs 60% for an atmospheric vented gas. A tankless electric only saves about 2-3% (standby losses) from an electric tank. There's no way to rationalize the expense of the massively increased electrical service - and the low gpm of the electric tankless whole house water heater.

A hybrid will cost less to use than a gas tankless - according to the DOE sticker (your milage may vary). There's less wait for a hybrid tank and plenty of GPM.

That's very helpful, thank you.

I had been thinking about doing the 50 gal + booster for high demand times, but knowing how low the tank standby losses are, I'll go with the 80 gal hybrid.