Adding baseboard heating to my current system.
I have in-floor pex in my house, but when I built the house, I stupidly didn't compensate for having about 1/3 of the house open to the upstairs, which means less floor with pex in it. So, my house doesn't get warm enough and I'm wanting to add baseboard heaters in the living room where there isn't sufficient pex. So, I need to tap into one of the zones I already have set up, but my living room zone already has 5 rolls (150 ft each? or whatever the standard is) of pex on it. My brother-in-law told me that I shouldn't put more than 5 rolls of pex on a zone, but is this true? What is the logic to this if so? My alternative is to create another zone with it's own thermostat, so I'd have two thermostats in the living room, or to add it onto another zone with less pex, but then it's dependent on the wrong thermostat. I'm not sure why it matters how much water you have running through one zone. Does it mean that it's taking the water longer to cycle through the boiler? I've noticed that one room in our house has only one roll of pex and it stays warm fairly easily. Thanks for any advice.
Edit: I could also add on some electric baseboard heaters, which would be much easier. I'm not sure how much less efficient they are than my gas boiler system.