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Old 09-30-20, 01:20 AM   #5
nibs
Apprentice EcoRenovator
 
Join Date: Jun 2010
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Have you done a heat loss calculation, if not you are groping?
A tankless water heater is a terrible choice, they are designed to put out short bursts of very hot water, inslab heating needs a steady stream of warm water. My own inslab system never heats the water past 110F even at 20 below, but spends most of the time idling along in the mid 80's or 90's.
Once you know how many BTU's you need, you can begin to design a system, you can work out your emitter spacing and your boiler size (BTU output).
I designed and built our system, spent a year studying everything I could find on Hydronics, and still did some things that I would like to take back. You need to study hard in order to get it right.
Best thing to do while studying is insulate under the slab with as much insulation as you can afford and insulate around the edges, become an insulation overachiever & your system will love you for it.

Last edited by nibs; 09-30-20 at 01:28 AM.. Reason: Added more info.
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