Are you warming to our water-heater discussions yet?

Second of two parts)

To continue last week's discussion of on-demand water heaters, we start with the knowledge that electrically-fired units are all but impractical for servicing the entire home. The amount of energy required is more than many homes can supply. Gas is a better choice for these applications.

Q: So that must mean a lot of gas is used also, right?

A: Yes, indeed. BTU required in full burn mode for the average whole-house system is 200,000. To put that in perspective, a furnace capable of heating a 4,000-square-foot house burns only half that amount of fuel. But the water heater runs only when you need hot water. From this, you can see why water heating is the second-biggest energy user in the home.

Q: Any other disadvantages?

A: Well yes, but they may be more accurately termed "lifestyle accommodations."

Q: You made that up, didn't you? What the heck is a "lifestyle accommodation"?

A: Let's say you're driving down the road and you notice people pointing, scoffing and laughing. It's apparent to all that you are driving a Toyota Prius. While it may be the ugliest car on the road, you remain confident in the fact that you are getting great mileage and creating very little pollution. It may be homely, but it does work!

Same thing with on-demand systems — you may need to make lifestyle accommodations ...

Gas units have about a three-second lag time from initial firing to hot-water production. This increases the wait time over a tank-type heater and produces cold bursts of water in the line if intermittent usage occurs (doing the dishes or shaving, for example). Turn on the water, wait for hot to rinse a plate, turn it off, pick up a plate and turn on the tap again several times, and you will get consecutive three-second bursts of cold water in between the hots.

The activation level of these heaters is usually about one half-gallon per minute. If you want a low and slow flow, you won't get it. If you want water to come out of a tap barely lukewarm, you won't get it without manipulation and adjustment.

Multiple fixture usage is limited. You cannot run the laundry, the dishwasher, take two showers and wash your hands simultaneously. Not that you could do that for long with a tank system, anyway.

At lower usage levels (shaving, for example), if cold water is used elsewhere in the building, reducing overall water flow to the heater, it may kick out of heating mode and you'll get cold.

Q: What about the installation issues you mentioned earlier?

A: For electric point-of-use units, you will need serious and expensive power lines to the unit. The gas/propane whole-house units will require new stainless-steel exhaust pipes and possibly a larger three-quarter-inch diameter gas line if not so equipped. These increase the cost by hundreds of dollars.

Darrell Hay is a local home inspector and manages rental properties.