Try propane. Buy a used tank. Gas issue solved. Also, more BTU's with propane than natural gas, I believe. Might be a permit issue in Seattle where they may not allow propane, but it wasn't here. All we had to do was the plumbing pressure test inspection. Tank goes in the back yard.

We have a 200 amp service on a 3300 SF house and use a high output tankless hotwater tank. We can have two showers going on any day of the year without issue. Our target temp is 130.

I ran a dedicated 20 amp/110V line for the hotwater heater. That was it.
I wired it based on how my plumber told me to do it and we have had ZERO issues with it in 3 years. You might want to check your sources for your info.
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