Heaters, how many BTU''s?

[DonDunn]

For a 37 foot sailboat, there seem to be 3 options: 6,000, 9,000, and 6,500 BTU.

Which could bring temp from 40 to 70? any? all?

Thanks,

[walt123]

As a comparison a 1500 watt 110 Volt ac heater puts out 5100 btus + or - hardly enough to warm up a uninsulated boat at 40 degrees Go for the highest btus you can get.