I have converted a garage to a family room with its own zone. It is 20 by 14 with an 8 foot ceiling. It has one interior door, four windows, and one 6 foot slider. One long and one short wall are exterior and other long wall has unheated garage on other side. Walls are six inch and are heavily insulated as well as floor and ceiling. cllimate area is eastern Massachusetts.
I have planned to put 16 feet of standard sized baseboard along the long wall behind the unheated garage. Is this sufficient or do I need more or less? Any other suggestions?
You need to do a heat load calc, then sizing is easy - compare the BTU/hr/ft at your supply temperature for the brand and style of baseboard you want, then just buy that. You'll be most comfortable when it isn't greatly oversized, as constant heat is more comfortable and ecconomical than when it is cycling on and off with long periods in between. But, then if the room is allowed to cool, you won't have enough to warm it up fast. So, there are compromises.
Heat load calcs are on-line if you do a little searching.
You need to know the worst case design temp, or make compromises. If you design it for -10, and it gets to -20, you'll never reach the desired set point.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013