On demand hot water

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Posted by Dave C on August 26, 2009, 09:37:09 PM

Hello,
I am building a off-grid home in upstate NY and need to install a propane on-demand hot water unit. Eventually I will incorporate solar hot water but given the fact I'm near broke, it'll have to wait.
The system I have is a 1K array with 16 Trojan T-105's. I see 6K per day in the summer and probably 3.5K - 4K in the winter.
I'd love to hear if anyone knows of a unit that only draws a mere trickle of electricity when not in use and only runs temp controls when in use.
I know Bosch makes one that turns on with water pressure but it's BTU rating is too small for our household needs.
175,000 BTU range would be about right and no standing pilot is a must.
Thanks with any input.
Dave C.

Posted by Tom Mayrand on August 27, 2009, 11:49:07 AM

Re: On demand hot water (Reply #1)

Dave, why do you have to install an on demand hot water heater? 175,000 BTU's? A normal hot water heater is only around 40,000 BTU's, and probably a lot cheaper to purchase and replace as well as to operate. You should consider solar first. If you are installing a PV system I would think that if you invest in a single or two solar hot water panels and run the pump off the PV system that the cost would be way more economical. If this is a vacation home and you are not there much, then there will be plenty of time to heat up a tankfull of water.
If you are building this home from scratch, then maybe you should consult with someone who knows solar. You could incorporate a sunspace to house the tank that can heat your home off season and while you are away and incorporate the hot water tank into this space as well.
Lots you can do besides invest lots of money into PV......

Posted by Dave C on August 27, 2009, 01:11:30 PM

Re: On demand hot water (Reply #2)

Tom,
It will be a year round home and my refrigerator (already in use) is propane as will be my hot water.
My "solar window," where my PV panels are located, is about 100' down hill from the house and is already beyond the re-design stage to accommodate for solar hot water (no mount, no roof, no-go)
Everything is up and running and I'm not buying any new PV panels (8-130 Kyocera's) to accommodate an on demand hot water unit.
I will definitely invest slowly into solar hot water in the future. One step at a time and I know propane is good back up (as is solar) to pump through radiant flooring when we are away on vacation (if ever)in our cold dark winters.
The BTU rating of 175,000 is needed given it will be our only source of hot water and the runs it will make throughout the home.
Thanks for the input.
Dave

Posted by Tom Mayrand on August 29, 2009, 09:21:34 PM

Re: On demand hot water (Reply #3)

Dave, 100' isn't that crazy of a distance for hot water. Just think of a large house with panels on it's roof. The runs from the roof into a basement can reach this distance in some cases. Now think of the Alaska pipeline. It delivers hot oil over miles. The trick is in the insulation. If you bury it below the frost line and insulate it may be possible to have SHW. Plastic water service pipe works well in this application. An insulated elevated line can also be done. Think of a chain linkfence with the hot water line as the top rail.
If the hill is south facing, panels can be installed upon an earth berm using the ground for insulation.
Are you installing a wood stove? Another easy way to make hot water. You mention radiant heat. In the summer you can gain heat from the floor and pump it into the tank, heating your water and cooling your house at the same time.
Just don't give up on SHW yet until you realize all you can do. As a plumber and mech. engineer, I am not a big fan of instantaneous HW makers. I've seen them come and go over the years. And when service time comes, you may find the manufacturer out of business. Taking a couple showers at the same time can be an issue. Also determine your water quality which may hinder materials used in the heater.

Posted by Dave C on August 31, 2009, 12:51:45 AM

Re: On demand hot water (Reply #4)

Without going into crazy detail about my site, it's just not well suited for SHW. I'm really just looking for information for off-grid on demand hot water. I'm dialed into everything I could do for SHW and have determined its just not in the cards at this time given the logistics and the money so.....
As of now I'm building an off-grid, strawbale, timberframe home I've designed and milled all the lumber myself and know the in's and outs of my site to that end.
Any input on a model would sure be helpful.
Thanks.

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