Frost protection setting

[Oz07]

What temp do you lot have your frost protection setting at?

Mine is apparently factory set at 1deg c but I am sure I have seen it not come on until 0 deg c

 

I want to knock it down a few degrees as I suspect this increases my heating loss due to the way the frost protection works (unbalanced?)

 

I suspect having a relatively cheap unit - Domus HRXD - I am safe to go down a few degrees as it wont be the most efficient unit (upto 86%) on the market anyway?

[MJNewton]

What's the setting actually a measure of? The reason I ask is that on my unit it can't be adjusted (not even visible) but it's never kicked in despite the outside temperature regularly sitting at -4C. I've put this down to the fact that the exhaust air in those situations has been, say, +6C and so the heat exchanger itself is still sitting above zero hence not at risk of frosting up. 

[Oz07]

Just says factory set of the incoming air at 1deg although can be set down to -15 I think