First, Rob and I had to figure out how many zones we wanted in the basement. Each zone is controlled by a thermostat, so all the rooms or areas in that zone would be consistently heated.
We decided we wanted the office to be one zone, the family room and bathroom would be a second zone and the bedrooms would be a third zone.
Then, Ray (over at Peterson Plumbing Supply) worked up our heat loss calculation. This is determined by several factors including the size of the room, how many exterior walls there are, and the number and size of windows and doors. I know there is more than that, but that's the simple version.
He determined how many loops of PEX we need for each zone, how long each of those loops need to be and the distance they need to be laid from each other. Then I took those calculations and started to design the best way to fit the linear feet of tubing into each room - from the boiler - through the room - back to the boiler in one continuous loop without crossing the lines. Each colored line in my drawing represents one loop. We had two loops in zone 1, two loops in zone 2 and four loops in zone 3.
If we had an exterior wall that wasn't covered by earth (which is two and one half walls of our basement) we needed to run the PEX closer to the exterior wall (two lines of PEX at 6" centers) and that tubing needed to be the line that came directly out of the boiler so it would be the hottest. As we moved into the interior of the room we were able to space the tubing at 12" centers. I couldn't run the PEX too close to the walls. I needed to run it through doorways and not under walls. I had to avoid the areas where cabinets were going to be installed. All of those factors played into how the design came together.
Some of the rooms were easier to configure than others and some of the areas I got too fussy about trying to make it perfect. Also, you can't bend PEX too tightly or it will kink so all those square corners are really rounded corners but VISIO doesn't do curves too well (at least not in a way that makes it easy for me to caluclate linear feet).
It was nice to have the design laid out ahead of time. We had to make a few adjustments as we worked but overall we stayed pretty true to the design.