On demand hot water

Posted by Tom Mayrand on September 02, 2009, 11:37:06 AM

David, if on demand is your choice, check out "Noritz". They manufacture on demand heaters. They make models that have direct ignition based on water flow. Operation power is 120 V using 115W or 250W if freeze protection is needed, so around 1 amp or 10 amp draw off of your 12 V solar PV system. They can be purchased at any local plumbing supply.

Posted by Dave C on September 07, 2009, 09:09:50 AM

Re: On demand hot water (Reply #6)

Thanks Tom. I will look into the Noritz line and see what they have to offer.

Posted by Thomas Anderson on September 10, 2009, 12:33:24 PM

Re: On demand hot water (Reply #7)

I highly recommend the Takagi TK-Jr. At only about $600 (+$300 for venting), it is very cost effective. You can also set it up as a closed combustion unit, as I have with mine, so that it draws combustion air from the outside instead of pressurizing the building. It tops out at about 140,000 BTU though. For me this is plenty since I have both passive solar in my house as well as a solar thermal system, which really doesn't cost that much if you source the materials yourself. I bought 3 x 30 evacuated tube arrays for $695.00 ea., plus $37.50 S&H ea., plus tax, for a total of $2,329.35. And I built a 900 gallon hot water storage tank for just a few hundred bucks (wood frame, styrofoam insulation, EDPM liner, cement board, and tile). You can put the evacuated tube arrays on simple ground-mounted frames. I would highly recommend more research into this route. Nonetheless, if you improve your insulation and infiltration and thermal mass in your house, you will probably find that 140,000 BTU per hour is plenty anyway. That's over 3 million BTU per day!

Posted by Thomas Anderson on September 10, 2009, 12:42:05 PM

Re: On demand hot water (Reply #8)

BTW, the Takagi uses a 120VAC electric ignition. As far as I can tell, it draws nothing until it sparks. Also, while the flame is actually going, it has a fan to actively vent the unit. The draw doesn't register on my Outback inverter however, so it must be miniscule, probably 10 watts or less.

If you're still at a stage to do so, I would absolutely recommend you install at least one wood-burning stove (I love my BIS Ultima, but any high-efficiency unit would do) as a back-up and top-up heat source. I wouldn't want to depend solely on solar or propane, just in case. I'm assuming that you have woods on your property (or nearby) and could thus collect firewood if you had to.

Posted by Dave C on September 11, 2009, 08:08:10 PM

Re: On demand hot water (Reply #9)

Tom,
Thank you for the info.
I'm looking in to the Takagi now and it seems to be well suited for my needs. I'm going to call the manufacturer and find out what the draw is when idle. I'm sure it's not much.
I'm looking at a larger model than the JR. and it draws less amps with a higher BTU range.
We'll be digging a well on Monday or Tuesday and depending on how much gallons per minute we get at around 150' (all we can afford) will determine if we need to build a cistern in the basement. If we do, I'd love to see photos of your design.
Thanks again,
Dave

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