Combination boilers provide the space heating of a boiler and household hot water heater in one appliance. This combination is more cost effective and space efficient than separate boilers and water heaters. However, combination boilers may not meet your peak hot water usage needs as noted in my section on water heaters. Perhaps you may want an additional storage tank or tankless water heater to meet your needs.
Condensing boilers convert more than 90 percent of their fuel into heat compared to only 70- 85 percent for the conventional ones. As with all condensing units a mechanical fan is used to expel the low temperature exhaust- often thru a sidewall. The cooled gasses create a condensate that must be moved to a drain or moved with a lift pump to a plumbing waste stack.