# Roof valley ice melt from below. Thoughts and help with circulator and plate heat exchanger sizing



## nlorntson (16 d ago)

Greetings.

We're contemplating a method to warm the underside of a somewhat flat roof valley using 1/2" pex, aluminum radiant heat transfer plates attached to the underside of 1/2"OSB and then covered in 1" closed cell spray foam. Something like you see in this picture.
View attachment 1073


The goal is to provide enough warming so on warmer winter days the heat from this will assist in warming the ice from below in the attic should a layer form, thus preventing an ice dam from getting a foothold. There are 7 roof valleys to address. Each loop of 1/2" pex ends up being about 300 feet in length between the ends that connect to the manifold. 

The valleys will never all be warming at the same time, just one at a time as the situation call for it. We do not anticipate running it to melt all the ice or snow, just warm from below to 35F or so to get things melting and then turn it off.

We'll be adding this demand to our radiant heat system already in place heating our house. That system was oversized to accommodate this addition.

Each valley area of spray foamed pex ends up being about 150 sqft. 

We expect to use a glycol mixture but don't know what percent yet.

*We're trying to establish what size circulator pump and braised plate heat exchanger we might need to perform what I'm describing*. 

Would love to hear your thoughts and comments on the idea but are really mostly interested in the pump and heat exchanger question rather than alternate solutions like electric heat tape on the roof, etc.

Thanks all for your help.


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