We love the tankless units. When sized and installed properly they are everything they are supposed to be. However they can be somewhat problematic to size properly and have a high initial installation cost.
PRO
1. Only uses energy to heat the water when the water is needed. This equals lower utility use.
2. Takes up less room in the area it is located.
3. The supply of hot water is endless. No holding tank to empty.
4. Tankless water heaters may qualify for tax credits.
CON
1. Higher startup cost than standard unit; this will be recouped with the savings in energy over time.
2. Gas versions may require upgrading the gas service and larger gas lines for the higher volume of gas needed when in operation. Electric versions may require upgrading of circuits and wires for the unit.
3. Some units are very strict on placement in the home; this sometimes makes it difficult to install/retrofit in an existing home.
4. Some complain that they do not meet high demand (example: shower with washing machine and dishwasher running.) This is avoidable if the unit is properly sized.
The decision to install a tankless water heater is a personal choice. While it is an expensive investment, it is certainly one that will pay for itself over time. You will also have the convenience of always having plenty of hot water. The downside is you won’t have the supply to operate several water demanding appliances at once. Some people already find that to be true with their conventional water heater, so it won’t be considered a negative feature.