Hubby installs AND services the Rinnai's, but there are a couple of things that you've got to watch out for on tankless water heaters.
1. The best ones are gas-fired (natural gas or propane) and need to be installed by a certified installer that understands the gas loads involved (ie. sizes the gas piping properly). Electric tankless waterheaters for the whole house are not worth the money - but may be worth it for camping. We install and service the Rinnai because they are the best quality and the most efficient - and no, they're NOT cheap.
2. Finicky. Yes, they can be finicky - if they are installed on well/spring/munipal water that is UNTREATED and has hardness/iron/etc in excess of the manufacturer's recommendations. (Yes, there ARE manufacturer recommendations for water hardness.) Have your water tested to find out what is going thru your pipes. Replacing a heat exchanger is expensive when it clogs up with lime - and may not be covered under the warranty. You will also have problems if your installer does not properly size the gas piping.
3. Understand that if you have long runs of pipe in your house, you will need to install a hot water recirculating loop. You will likely have delays in getting hot water.
4. Get to know who is the service provider in your area as you may be calling him/her to service the unit annually or bi-annually. Our recommendation is to flush the units annually with vinegar so that it dissolves any calcium / lime.
On the flip side, these are extremely efficient units and can be well worth the price in cost savings.
AJ
www.clearcreekwaterworks.com