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uninsulated (almost) brick building

So I'm getting ready to tackle my largest radiant project yet, and am trying to settle on the best controls for the application.

Here's the scoop:  Old brick building being retrofitted into 7 one bedroom apartments, with radiant heating in each, single zone per apartment.  3 on ground floor, 4 up.  first floor will be new concrete slab on top of 2" insulation on old slab, upper floor will most likely be Warmboard with engineered hardwood and tile on top.

The tricky part on this is figuring the heat loss.  The building will have 10" cellulose in the cieling (2x8 rafters with furring strips below to decrease bridging and allow more insulation.  When the roof is re-done, there will be 4" foam above. 

The walls are 8" solid brick upper floor and 12" first floor.  there will be 2" XPS on the outside of the walls with new siding over that.

What's the best way to calculate the heat loss thru that thick of a wall with insulation on the outside?  I've been using Uponor's CDAM for sizing, and then building a safety margin.  as we usually target water temps of 110 F and lower, we've usually got plenty of room to increase temps or reset curves if necessary.


I'm considering the Uponor T-75 thermostats with constant circulation and motorized mixing valves for each apartment, but with the low mass floor upstairs, and super high mass walls, I don't know if that's the best option.


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