1. These units optimally work if you are also willing to install a hot water recirculation system. Otherwise the wait time to get hot water is ridiculous. Points of service that used to take mere seconds will take SIGNIFICANTLY LONGER with a tankless. You'll also notice that your water temperature may fluctuate quite a bit. If another point-of-service (tap or appliance that uses hot water) is opened, you'll notice a huge drop off in the water volume and water temperature.

2. The units make a lot of noise. If you cannot mount the unit away from living/sleeping areas, you'll be sorry later!

3. You may need to install new shower/sink fixtures for the unit to operate properly. Generally there is no problem with double handle faucets. You are much more likely to have a problem with a single ball faucet. The problem is that the tankless units only pump through a few gallons of hot water per minute, so the pipe pressure is much less than the cold water pipe. Unless your single ball faucet has some sort of hot/cold water balance mechanism, I can almost guarantee you will be taking cold showers. This imbalance can also make precise temperature adjustment difficult.

4. Typically, a 1" gas feed is required if you also have a furnace on the order of 100,000 BTU or above. Most older construction does not have 1" gas pipe -- a common standard is 3/4", which means new gas pipe needs to be run from the gas meter to the point of delivery (furnace and tankless water heater). Be sure to ask your installer about this!

5. Your gas meter may also have to be replaced to handle the added demand of these units. When they're cooking on full, they're burning around 200,000 BTU...that load, along with your furnace, may be more than your gas meter can handle. Even with a meter upgrade, it may be more than your gas company can deliver in terms of pressure. Check with your local gas vendor. Additionally, some municipalities require installation of a seismic (earthquake) gas shutoff valve to be installed any time a new gas meter is installed. In our case, that ran an additional $350.

6. Any time you momentarily turn hot water off, you will experience what is called the "cold water pocket." This happens because when the flow is disrupted, the unit shuts off. So cold water runs through the unit until it once again senses the flow and cranks up the gas jets to warm the water. For us, this is about a 3-6 second process. May not seem like a big deal, but when you're taking a shower and get blasted with 5 seconds of cold water...brrrrrrrrrr.

We had one of these units installed earlier this year and have been very disappointed. Our heating & AC salesperson promised us the world, but it seems very few of them actually LIVE with one of these units. They simply don't know what the heck they are selling, as well as some of the negative consequences homeowners will inevitably run across. Also, we have not noticed any appreciable energy savings. I wish we could turn back the clock and put in a traditional gas tank.

The bottom line: If you're considering installing one of these things, make sure you try it out in someone's home FIRST. Measure how far your vital points-of-service are away from the unit and decide if the delay is acceptable to you. Determine how many faucets you may need to replace. Check your incoming gas line and meter and check with your local utility company to ensure your home can accommodate one of these dogs. For most consumers, unless you are willing to have a recirculation system installed to complement the tankless YOU MAY BE DISAPPOINTED IN THE PERFORMANCE!