Old Decommissioned Water Heater Tank In Front Of Tankless

When we had a tankless water heater installed a couple of years ago the motivating factor for the change was that one of our two conventional (tanked) water heaters was leaking.

I had them leave the non-leaking water heater tank in place (it was totally decommissioned) plumbed in before the tankless. So it goes Street->old tank->tankless. My thought was that I might as well have 40 gal of unheated water coming up to room temperature before it goes into the tankless. So theoretically it's taking the first 40 gal of water to be heated from ~60 to 120 as opposed to the temp that it comes in from the street at - ~40 or so?

I'm having a bit of remorse on this decision - because I'd like the floor space that this non-working tank currently occupies. It's not critical I have it, but it would be handy.

Have you heard of this kind of setup being done before and, if so, is it practically an advantage or is it all to theoretical/minor? I'm considering taking this tank out and having it go street->tankless - like I assume almost all installations are.

Thoughts?

Thanks!

Jim

You have a...

WH- Inlet Water Tempering Tank

Water heater tanks generally have insulation on them to retard heat loss, but the insulation will also retard heat gain. Your current arrangement might help out a little bit when there are long periods between hot water usage, but only a minor amount.