The dew points the last few days have been below zero, so any moisture left will create a condensation cloud. May be normal. Although, it does sound like you have a much bigger boiler than required. If it is keeping the house comfortable with the outside temps we've been having with only 139-degree water, it's probably too big, maybe by a factor of two and likely more, which means it will never reach max efficiency. If properly sized, it's likely when it's near zero F out, it couldn't keep the house warm unless the water temp was higher.