I told my guy I wanted 5 inches.. so I would get a solid 4. He did close to 8 in places to make sure I got my 5! After they were foamed... I was still losing a lot of heat around the valves that he had kept the foam off. So I boxed the whole works in with studs and 3/4 inch plywood. Filled the box up with blow in cellulose. I've had to get in to one part to clean my sticky aquastat once.. but it wasn't so bad. I have to replace one temp probe this summer when it gets a bit warmer outside. Setup is good.. I don't have near the losses you are talking about.