How many BTU you need to stay warm in your truck, RV or a boat? Well, there’s no universal formula that would give you a definite answer. Unlike residential or commercial space, marine and automotive applications may vary widely from case to case. The main factors are temperature difference, humidity, quality of insulation, number of windows and volume of air you want to heat. Outside temperature is the one that has the biggest impact, so following climate map should help you to get in a ballpark area:
To get your number, find your demand in BTU per cubic foot of air, then multiply it by a number of cubic feet you want to heat. Consider other factors like insulation, fresh air supply etc. Remember: this is just a reference and we cannot guarantee that the number you get is going to work in your case. Reasonably oversized heaters last longer, work less and heat space faster than a “bare minimum” solution.