"Is it possible to drain a tankless water heater to prevent freeze damage when not in use?"
Yes. Simply drain both lines 'to' and 'from' the unit. As long as there are no check valves in the way, that should drain the water from the unit. To guarantee that there is no water in the unit, we recommend two drain valves - one before and one after the unit - as well as blowing air through the water line.

"If these units don't have a tank, how do they know when to turn on?"
The tankless water heaters have a flow switch built into them. When you turn on (open) the hot side of a faucet the water then moves (travels). Once the water is traveling at 3/4 of a gallon per minute or faster most tankless water heaters switches will then turn on the gas or electricity.

"I would like to convert my natural gas tankless heater to be able to use LPG (propane) gas instead. Do you offer a conversion kit?"
Sorry, but we don't. Even if we could, we probably wouldn't, as in most cases it is not a good idea to convert one type of gas for another. Burners can be different, orifices, etc. Not only is the BTU rating different for these two gases, but also the heat of the flames and a number of other factors. We simply do not wish to sell ("profit from") something that might create a non-safe environment.

"There are many companies selling all kinds of tankless water heaters. Why should I buy a tankless gas water heater from you rather than elsewhere?"
We are a large, reputable company that was here yesterday and we will be here tomorrow. We are often copied, but we don't believe that any one can match our service and certainly our base of satisfied customers is larger than any Internet plumbing supplier since 1995. We sell 1000's of other quality plumbing products as well, so you can rest assured that we know plumbing products. We are a very stable and reputable company. We love to sell what we believe in, and we definitely believe in Takagi.

"What's the difference between a conventional flue and a direct vent?"
A conventional flue is what most people are familiar with. It typically consists of a double-wall flue pipe going from the top of the heater through the roof, venting outside. The fixture draws its combustion air from the space around it (utility room, garage, hallway, etc.). A direct-vent unit on the other hand, both vents and draws its combustion air through a specially designed pipe from the outside via an adjacent wall.

"Your products specify the 'temp. rise' based on the GPM flow; what do you mean by this?"
Temperature rise is the amount the heater raises the temperature of the incoming water, based on the flow rate shown of that water.

"Will an on-demand water heater save me money on my utility bills?"
If your current water heater is electric, then yes. However your savings will vary depending on your local cost per KW hour.
If you're using propane, it might save you money. Again, it depends on your local propane cost.
If you're using natural gas, then probably not. You will save natural gas, but the extra money spent on a tankless heater will probably not justify the savings.