Re: tankless water heaters
Posted by mss on October 11, 2001 at 01:24:23:
In response to Re: tankless water heaters
I've been running a tankless heater from TAKAGI for several years. Love it but you must be aware of a few things...

1: Turning on the hot tap for even an instant fires the burner and heats water in the standard installation. My mother in law spends a great deal of time at my house and she has a habit of turning on the faucet about 50 times a day. This causes the water heater to cycle excessively and literally wore out the porportional gas valve in one year. This constant cycling also blows any extra efficiency that the tankless heater has right out the window- thus not saving you any money.

2: Demand fired hot water is hard to control- water takes a few seconds go from dead cold to hot and the first few cups of water is generally not at the "set temperature"- it's usually hotter. This can be a problem (or dangerous) if you have kids or sensitive adults in the house. I added a mixing valve to regulate it.

3: In daily use, with multiple bathrooms with several residents in the house, you will not like the way a demand water heater works. Flow is limited- in my case to 5.5 GPM at 140 degrees F- Turning the water on or off and possibly having two faucets turning on or off at nearly the same time can result in a "stuck" or fooled demand controller resulting in no hot water or T&P valve opening. Once the T&P opens on a demand system, the heater will run until your gas bill comes if you don't notice it.

My current solution is: I put a regular water heater tank in a loop and use the tankless unit in a traditional boiler setup. I'm using a circulator hooked to the thermostat in a 25 gallon water heater tank to provide the "demand" to the tankless unit. This buffers the constant on-and-off of faucets and prevents cycling problems in the system. I also circulate hot water in a loop so that no faucet in the house is more than 2-3 seconds away from full hot water. The circulator is on a timer so that the loop shuts down when we are less likely to be needing hot water.

All in all, I would not do this again. My next domestic water system for my own use will consist of 2 40 gallon gas tank type heaters and a circulator. The tankless unit is expensive, excessively complicated (keep it simple stupid!) and requires occasional attention to keep it operating. Tank type heaters usually run for years without touching them and I could do my entire dual tank installation for about half what the tankless unit cost alone.

I do enjoy the endless hot water though, when it works.

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