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Old 11-17-2007, 04:26 AM   #31
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Ideal temp for water heaters is 120 F.

I live in Maine: our waters have so much mercury that pregnant women and children are recommended not to eat locally caught fish. This is due to power plants emissions and power plant emissions only. It IS a big deal.

For you folks with huge bills you must live in hot climates and run A/C. A better strategy is to keep the house closed up and shades drawn during the day then open windows at night. Look into reflective barriers in the attic, etc.

Programmable T-stats can save 15-20% easily (my experience with several buildings).
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Old 11-17-2007, 07:41 AM   #32
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Actually, rather than letting shower water pool in the tub and having to deal with excess humidity than can cause mold, there actually is a thing called a gravity film exchanger, or GFX, that can be used to add some of the BTUs of the water going down the drain to warm up the water going into the water heater and also into the cold side of the shower.

I am SO GLAD this subject was brought up! For the last week and a half, I have had the wall opened up below our two shower drains for a remodel and hadn't even though about this. It was a bit of a head-slapper moment for me. The trick now is finding/building one for a reasonable price.
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Old 11-17-2007, 11:05 AM   #33
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The exchanger works by pre-heating the cold inlet side to the water heater.

If the supplier's claims are to be believed, the main benefit is in expansion of virtual hot water capacity. They are attempting to sell it on a cost basis which works out to $10-$20 month for a family of four, but I see even greater potential benefit by downsizing the water heater, as they are claiming potentially triple the hot capacity.

So even if one were to cut the size of their water heater by 1/3, they could still double their useable hot capacity with one of these things installed and save money doing it.

And in my house there really isn't any such thing as a 'quick shower'. :P
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Old 11-17-2007, 11:08 AM   #34
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Ideal temp for water heaters is 120 F.
Depends upon what you consider "ideal". Yes, 120F is what we have been taught (by well meaning officials) to use. And if you have people in the house who are in danger of using hot directly (and therefore "scalding themselves" if the "hot" is "too hot"), than it can help protect your family some. However, there are good arguments for running with a much hotter temp (I run about 155F in our house).

For one thing, 120F is a great temperature to breed "Legionnaire's disease" (among other problems) in your plumbing! For years (after those 120F recommendations came out), public health officials didn't know why people were getting sick. And it was latter traced to the fact that 120F (as well as the slightly lower temp that occurs when a 120F system starts cooling down when hot water is being drawn), is just a great temperature for breeding some forms of harmful bacteria! Hotter plumbing temps tend to burn out the harmful bacteria, and lower temps tend to be "too cold" to grow/breed the bacteria in the first place. So from a health/safety standpoint, you are much better off with hotter water in your system (provided you have some protection against "scalding yourself" at that tap).

Also, keep in mind that if/when you routinely run your tank hotter, you have more overall ability to use hot water (i.e. for a given amount of hot water, you can either use a much bigger tank, or run the tank a little hotter and therefore have the opportunity to mix more with "cold"). And its also a little easier/quicker when cooking, to be able to start off with water much hotter from the tap (especially when you need to boil something).

Of course, we are on a energy efficiency board here, so the claim often comes up that lower hot water temps save energy. However, the surprising thing, is that (from an energy usage standpoint) it mostly balances out (with little difference in total energy usage, no matter which temp you set your hot water heater at). The reason for this, is that while lower water temps use less energy to heat the water, they also cause you to need to use MORE hot water as a result (as you have less opportunity to mix the hotter water with "cold" when you use it). So the overall energy for heating the amount of water you are using is about the same (as you either heat less water hotter, or more water to a lower temp point).

OTOH it is true that with a traditional tank water heater, going with hotter water (in the tank) will result in more heat losses around the tank itself (as hotter water in the tank, will tend to loose heat quicker). However, if you properly insulate your hot water tank (which is cheap to do, and worthwhile no matter what temp you run your hot water system at), the extra heat loss (due to the hotter water temp) should be negligible. So while in theory the costs are higher with a tank at a higher temperature, in reality this isn't a significant issue for a well insulated hot water tank.

So really, it shouldn't matter much from an energy using standpoint what temp you set a (properly insulated) water heater at. But while the energy usage should be about the same no matter what your temp (unless you use the excuse of the higher temp allowing more total hot water capacity to use more total hot water), the temp does matter a lot to both your health/safety and the overall usability of the hot water system itself.
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Old 11-17-2007, 11:10 AM   #35
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clench, these units really work best in dorms and locker-rooms. The payback is way way out there. My math may be wrong but at 2.5 GPM x 8.33 pounds per gallon it is gonna reduce your energy 21 BTUs per degree rise. On a 5 minute shower with a 3° rise, that's a penny or so depending on how you heat your water. In a family of 4, that's maybe $20 to 30 dollars a year on a $500 investment. The manufacturer's numbers are far better than mine for some odd reason.

That $500 would probably be better spent on solar preheat, but there are BTUs there for harvesting if someone wants them.

Snax, the price of copper has taken the price on these through the roof. There's one knock-off company out there - Canadian I think, but their prices aren'y much better - sorry can't recall the name. A pex based solution would be nice for price but the efficiency would drop a lot.

When I redo the plumbing for the baths, I'm gonna see if I have room below the lowest fitting for a 30" version.

Edited:
This is the company with the knockoffs.
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Old 11-19-2007, 03:04 AM   #36
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One device used almost everywhere here in Sweden these days, are heat exchangers on the ventilation system. This makes it possible to ventilate properly without energy losses. I think this is standard equipment on all new buildings over here.

Another interesting concept that is studied and piloted extensively in Sweden and Germany is the "passive house". These are houses that requires virtually no heating. They only use the dissipated energy from people and household appliances. The houses are heavily insulated and designed to minimize losses and take advantage of solar influx. The classification "passive house" requires that the installed power is less than 10W / square meter.
This has been shown to work very well, at least in the southern third of Sweden and the houses are now being mass-produced.
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Old 11-20-2007, 02:57 AM   #37
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Just for the sake of it, I looked into the legislation and numbers for buildings here in Sweden. The law says that a newly built house can't use more than 110 kWh/square meter and year. This includes heating and hot water but not household electricity.
Heat exchangers on the ventilation system is not yet mandatory. If it was, the maximum consumtion could be set at 90 kWh/sqm and year. The German classification for passive houses is as high as 45 kWh/sqm and year (Sweden 10). Building passive houses is rather low-tech btw. All it takes is good insulation, tight walls and doors, energy efficient windows and heat exchanging ventilation.

Anyone knows what is the average energy consumtion of an American house?
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Old 11-20-2007, 06:48 PM   #38
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That's a low standard. Translated that works out to 35,000 BTU per square foot per season. Suppose 7000 HDD per season and that works out to 5 BTU/HDD/SF and mine is around 5 and that's with a Euro boiler and a fairly tight house and actually a bit fewer than 7000 heating degree days (easily searchable for your area). It was around double that before upgrading. That's tight enough to require mechanical ventilation systems, definitely the German passive spec.
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