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mtimmer_gw

How much flow from a tankless do we need?

mtimmer
9 years ago

We're doing a gut remodel of our house, which includes the installation of a tankless water heater, in particular a Navien model with built-in recirculation. Navien produces three units and based on raising the tap water by 62 degrees (from 58 to 120), the three units can crank out either 5, 6 or 7 gpm. (That's my rough estimate, based on Navien's specs.)

I'd like advice on the proper size of the unit. Our plumber is recommending the biggest: he says that the biggest versus the middle unit is an incremental $200 and it's worth it to never worry about having enough hot water flow. While I like the certainty of that, I'm also worried that it's overkill: we are a family of two in a 1,500 sq foot house with two bathrooms abd relatively little simultaneous hot water usage. I have a hard time thinking the biggest unit was designed for households like us. We also have flexibility to make sure we're not showering when another major hot water use is going on, such filling the tub or washing clothes/dishes.

Last data point: we live in Southern California and I'm using 58 degrees (best guess) as the temp of the incoming water. Not fully sure if that temp is correct, but it seems reasonable.

Thanks for any advice!

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