Hot Water


    I know it’s been addressed before but what are the pros & cons of ‘on demand’ hot water heaters? Are they complicated to install? Need major modification of existing plumbing where there’s been a normal gas tank?

    9 Replies

    1. I remember the same postings DIBS does.

      I read them and my memory may not be perfect, but I think the upshot is the on demand ones are good for places where you need hot water only occasionally–like a weekend house or something like that. Not so good for regular use.

      A vast oversimplification I’m sure. Those old posts would be worth looking up.

    2. Most on demand water heaters aren’t installed the proper way. A small electric water heater(6gal) should be installed as a buffer tank so cold shock doesn’t zap the on demand heater at initial start up. Also the buffer tank helps bring hot water up to you faster. Most people don’t read piping instructions when they’re installed. Over all I think they suck. I sell a few here and there and have nothing but problems with them over the years. Get a high efficiancy boiler with a indirect water heater. You can’t go wrong.

    3. “Electric ones take up three double breakers in your panel. I have never seen a panel that has three double breakers not being used.”

      Don,t even waste your time with electric on demand hot water! Huge waste of money. Generally they run on 3 30 amp circuits at a full eighty percent capacity. I have been on several service calls to fix these things, and a year later I’m back replacing another element/circuit board.

      The gas ones are great if they’re in proximity to your bath, but you end up taking longer showers. Longer runs need well insulated pipes. You can double them up for longer runs, but disabling the thermal sensor on the second unit voids the warranty on the unit, uses twice the gas, wears the unit out faster, and requires more adjustment at the shower/sink valve.

    4. I lived in an apartment with a gas ‘on demand’ unit for both heat and hot water. Perhaps it was installed incorrectly but it stopped working at least twice a month. The landlord finally had to remove the whole system and put a boiler in the basement.

    5. Energy savings depends upon frequency of usage. I believe either Steam Man or master Plumber have posted a long disussion of the pros and cons in the past. It may not be under plumbing but under Utilities or another topic. I believe he’s posted it more than once, with links to other analyses as well.

    6. I’ve had quite a lot of trouble with my gas tankless heater (a Rheem). It seems to require repair every six months or so. The burner gets clogged up with debris and the unit will only run for a few minutes before it senses a problem and shuts down. I’m on my third burner unit. The techs at Rheem say that you should clean the burner unit periodically. Unfortunately, this requires a complex disassembly of the unit — either 2 hours of my time or an hour or so of a plumber’s (expensive) time. This may simply be a consequence of Rheem making a crappy product. However, all tankless units need to be flushed twice a year, which is also either time-consuming or expensive. I haven’t noticed major energy savings over my old tank heater; certainly not enough to compensate for repair costs and aggravation.

    7. Mine would be gas & there are 2 floors between tank & bath – guess it’s not a good choice. Thx.

    8. The gas ones are supposedly great, but have heard the water is often not as consistently hot in remote locations of the house.

      Electric ones take up three double breakers in your panel. I have never seen a panel that has three double breakers not being used.

      Biggest pros are the energy savings (which some say are not really there) and the space savings in the utility closet.