Unlimited hot water

[Bikewanderer]

For those who are writing that on-demand water heaters can't keep up with 2 showers, or 1 shower and 1 dishwasher, etc., maybe their water heaters are undersized. Like I wrote a few posts back, we have a Rheem RTG-84DVP. We often have 2 shower heads on simultaneously -- no problems.

You have to look at the Delta-T flow rate curves for the heaters before buying to calculate it that heater will handle the flow of 2 faucets at XX delta-T. Example: incoming water temp is 45 deg and output goal is 120 deg, therefore delta-T is 75 deg. 2 faucets at 1.5 gpm = 3 gpm minimum. Our water heater does 4 gpm for that delta-T on the graph.

Could it be that some unsatisfied customers just bought what the store had on the shelf and now it underperforms?

Marcus

45 degree incoming temperature is optimistic for many of us. You're also optimistic on GPM. A modern shower head flows 2.5gpm. Older ones can flow twice that number. Granted, most people don't shower at 120 degrees either. Mine is 110-115 degrees, so I use some cold water to temper it. I'd guess I use 2 GPM of hot water in the shower. The wife and kids a little less - 1.75GPM. 4GPM would be doable and in my mind would have limitations similar to what we have now with the tank style. I have 80 gallons in the first hour and we only use it if we are doing baths, showers, laundry, and dishes at the same time. That generally only happens saturday morning. We've just adjusted our habits to wash cold water wash first while we are in the shower and if all the kids are taking baths I'll toss a pot of water on the stove to help with that last bath that inevitably ends up cold.

We could probably get it to work, but I'd imagine that if two showers were on and another person used hot water it would get cold in a hurry.

My biggest thing is that I'm not convinced that energy useage is significant. I once shut off utilities at a rental house and came back over two weeks later and found still warm water in the tank. It was winter. In summer I rarely go over the minimum billing on the gas even with all the people in my house, so the savings would be nil there.

I'm glad you guys are happy with them though. To each their own!

 

[charlz]

Here's how my system is set up, if anyone is interested. The plumber was skeptical, but no problems yet. Because my storage tank is under the house, I don't have to worry about incoming water temps in the 30's like some have mentioned. The tank temp never get's below the 50's even without heat input.

I have thought about doing a solar thermal system to, at a minimum, pre-heat my incoming water before it gets to the HWH. Any code issues etc. having a water tank under your house? That is about the only way I could do it as my HWH closet doesn't have enough room for another tank. I was thinking of using a regular heat exchanger type tank in the crawl space and super-insulating it.

For your setup do you have a way to check the water level/add make up water to the storage tank to compensate for any evaporation etc?

 

[schweizer]

Code requires double wall between any antifreeze (even propylene glycol) and potable water. My tank system meets that criteria because the "heat sink" water is between the potable preheat coil and the solar/woodstove coils.

The plumbing inspecter sort of ignored my weird tank and pipes. "As long as it doesn't have to do with the potable water," he said. I connected it to the tankless after inspection.

The county required plans re-checked and stamped by an engineer because I put the tank only a few feet from the foundation and it was added to the house at the last minute. I had to put gravel around the tank with a drain pipe under the foundation, and compress it with a "jumping jack" all around. None of that was a big deal because gravel was put down under the concrete slab anyway.

Yes, there is a manhole to the tank in the corner of garage. Evaporation is minimal though. Thanks for reminding me that I need to check the water level.

I was thinking of using a regular heat exchanger type tank in the crawl space and super-insulating it.

Yes, that would work. You could use an all in one tank that have solar coils built in, replacing your regular tank -- they are quite a bit more expensive than a regular water heater tank, though. I wanted 2 separate inputs (wood and solar), and a lot of heat storage (i.e. 500 gal). The concrete septic tank was relatively cheap, I had most of the foam insulation already, and flexible copper coil was not that expensive. That's the reason why I went down my route.

Marcus

 

[dave1949]

I have thought about doing a solar thermal system to, at a minimum, pre-heat my incoming water before it gets to the HWH. Any code issues etc. having a water tank under your house? That is about the only way I could do it as my HWH closet doesn't have enough room for another tank. I was thinking of using a regular heat exchanger type tank in the crawl space and super-insulating it.

For your setup do you have a way to check the water level/add make up water to the storage tank to compensate for any evaporation etc?

If you have enough sunshine, the trend seems to be away from large storage tanks that act as pre-heaters or storage, unless you are looking at solar radiant heat. What seems to be recommended are dual heat exchange tanks in the 80-120 gal range. That makes some sense as a reasonable trade-off, since anytime your large storage tank temp. is low, the btu's needed to be produced by solar become huge to raise the temperature of a large volume of water. One of those dual heat exchanger tanks would replace your existing tank and are usually small enough to fit. They generally add capacity by making them taller more than making them a lot larger in diameter.

In the OP's case, he is getting the job done now by combining wood space heat with hot water. That makes sense for his application.

 

[schweizer]

anytime your large storage tank temp. is low, the btu's needed to be produced by solar become huge to raise the temperature of a large volume of water. One of those dual heat exchanger tanks would replace your existing tank and are usually small enough to fit.

Yes, exactly. What I didn't write is that I've been thinking about decreasing the size of my tank a bit, maybe half to 250 gal.

 

[wawajake]

This is unit I had installed this summer. It is propane and does my potable hot water and all my radiant heat for house. It is a European brand called Larrs.... rated at 125 MBTU/h. and uses new kind of 2 inch PVC for exhaust and intake. The professionals had difficulty getting the settings right at first because it came from factory set for natural gas , and it is not set by orfice size it is set electronically to change to propane. Eventually they gave up and ordered another unit set by factory to propane, it arrived a week later. Has worked great since. We will see how the first winter goes, but it seems up to task so far. But they are expensive. I switched from a wood boiler (the chimeny is still seen in the pic.)

 

[mistermcgoo]

We installed a geothermal closed loop system in 2010. So far it has been a very good investment in our view.

We live in the thumb of Michigan. Our first complete year of heating/cooling and hot water cost under $600.

Our water had high iron, manganese and calcium; very hard. It was ruining all our new appliances (did major home remodeling in 2010) at a rapid pace. Even the expensive Kohler faucets were failing. I found this place Water Softener Systems, Iron Filters, Water Treatment Systems for Home or Business. , sent them a water sample and purchased one of their systems; installed myself. There is no maintenance required. No more iron stains and sulfur smell; water tastes great. According to a test done at the local hardware store, our water is 17 gpg calcium; very hard. Having no room after installing the water filter system (and where the dogs stay), a traditional water softener was not much of an option. I decided to try a ScaleWatcher electronic water conditioner. After 7 months there has been no buildup of calcium on any faucets, tub, toilet etc. It cleans off with little effort and does not stick. I've heard it said these setups are a scam, but with a one year money back guarantee it was worth a try. So far its working as advertised.

So I have to say after 20 years of battling very hard water, not to mention the iron/manganese and bad smells, I believe the battle has been won.

One suggestion to those with hard water. Do not bother with a water softener until the water is properly analyzed and filtered before the water softener. I ruined two water softeners over the years before learning that.

P.S. We burned corn for 5 seasons until corn became too expensive; thought about an outdoor wood burner......then the flashbacks returned from the days of cutting wood.