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Recirc loop, tankless heater, problem with direct home run

Posted by drtechno (My Page) on
Thu, Aug 19, 10 at 13:20

Hi all

We are going with two cascaded Navien 240A tankless water heaters, and are concerned about the problem of waiting long periods of time for hot water. Now I know the A versions have a recirc tank which should help decrease the time of delivery, but I don't think we can run a recirc loop in our house, which I just realized.

We are plumbing a direct home run system with manifolds, and therefore, any recirc loop will only take care of one run. In typical plumbing, the wait time for hot water is reduced as hot water lines off the recirc trunk are ready to go. However, in a home run system, there are no common trunks... only the recirc loop run will have 'instant' hot water.

Am I correct in thinking that, since the home run system only heats one trunk, it is useless in decreasing hot water delivery time in other trunks? I think its the same problem even with the Navien A models, in that the cold water in the direct home run trunk needs to be purged prior to hot water arriving.

Follow-Up Postings:

RE: Recirc loop, tankless heater, problem with direct home run

You are correct, but you will have hot water at least to the manifold decreasing the time it takes to get from heaters to it. The benefits of home run systems is smaller pex pipes to each fixture. Smaller pipes mean less water thus the hot water will get there faster than a conventional piping system.

Many will only recirc to the hot water manifold, especially if it is located a distance away.

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