AirWorks

Heating and Cooling Solutions



Demand Hot Water

Dear Comfort Advisor,

I will need to change out my older gas water heater soon and since it is just me the wife at home now, I was thinking one of those “on demand “units might be a good idea, but I really don’t know much about them. Can you shine some light on this for me?

Dear Tankless Tom,

Demand water heaters (also referred to as Tankless or Instantaneous water heaters) can be energy savers because they only heat water when called on so they don’t produce the standby energy losses that occur with conventional storage tank heaters most of us use now. And because they don’t have that large storage tank they can be a real space saver too. Many advertise that they supply “endless hot water” but be aware that there is a flow rate limit, so even the higher rated gas-fired models ( at 5 gal/minute) cannot supply enough hot water to satisfy simultaneous, multiple calls for hot water. For instance, when multiple showers are running (pretty typical at my house every morning), and the dishwasher or clothes washer are also running. In smaller households like yours, that is probably less of an issue and in larger households multiple units can be a solution. So, why aren’t these units all over the place? COST!

A demand water heater can easily cost 3 to 4 times more than the run of the mill water heater. This is because the unit itself is much more expensive and the installation is more complex for several reasons. The gas line serving your existing water heater, only has to deliver about 35,000 BTUs. A demand water heater will need 150,000-200,000 BTUs, so you’ll need a good gas pipe fitter for the job. They also require specialized vent systems. On the electric models, you’ll need a 2 to 3 30 amp/230 Volt circuits installed. Hopefully there is room in the breaker box.

Another matter to consider is maintenance costs. Hard water is no friend of any water heater, but is a real problem for the demand systems. Regular flushing with vinegar is necessary and a water softener is highly recommended. There are inlet strainers that need to be cleaned regularly too. Cleanliness in the water system is important because having good water flow through the unit and you home distribution system is critical for proper operation.

This is an important consideration for older homes with galvanized water piping. You would be surprised and disgusted to see what is inside some of those old pipes. Also, consider the availability of parts that might need to be replaced in the future. You might find the water heater online or at a large box store, but what do you do if you need a gas valve? Remember you might need to go several days without hot water if you are waiting for a repair part to be shipped in from Timbuk2. So do your homework on brands and models.

Another important concern, especially for the electric models, is the fact that when they call for energy, they really call for energy. Not great news for the electrical grid when thousands of households are demanding hot water for showers between 6-8 am or for dish/clothes washing from 6-8 pm . Those “storage tanks” are pretty helpful on that front. And the newer storage tank models are insulated pretty darn well so those standby losses aren’t as bad as they used to be. I hope this has shed enough light on the topic that you can make the best decision for your circumstances. You call always give me a call at 257-1341.

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