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Old 11-09-2012, 09:09 AM   #41
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If in a cold climate, half the year the lost heat is used to warm the house.

If in a hot climate, not so good.
Yes, it is a hot climate so it is bad. There's got to be some electrical load on both the circulating pump, and the air conditioning.
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Old 11-09-2012, 10:09 AM   #42
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Yes, it is a hot climate so it is bad. There's got to be some electrical load on both the circulating pump, and the air conditioning.
One option is to use a timer on the pump to minimize loss during down time.
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Old 11-09-2012, 10:46 AM   #43
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If in a cold climate, half the year the lost heat is used to warm the house.

If in a hot climate, not so good.
Doubt this contributes to our overall AC load. Our pipes run under/through our concrete slab.
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Old 11-09-2012, 12:48 PM   #44
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Doubt this contributes to our overall AC load. Our pipes run under/through our concrete slab.
The heat taken from the hot pipes and into your slab doesn't disappear. It's making your floor warmer and increasing your AC load somewhat. Figure about 2/3 of the "lost" heat is warming the floors and increasing your AC load (the rest is warming the soil under your slab somewhat, being slowly conducted away through that soil). It takes about .3 watts of air conditioning (at typical efficiencies) to remove one watt of heat gain from other sources (your gas hot water heater via this hot pipe). Given the typical difference in cost (per watt) of electricity vs NG, it's likely that, in a climate where cooling is required, a circulating hot water system in the slab is costing about as much in electricity (for AC use) as for NG to heat the water. And then there's the electricity used to run the pump (oh--which also generates heat. Not a factor if it's outside the conditioned envelope).
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Old 11-09-2012, 01:02 PM   #45
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You may be able to install a pump that is operated with a proximity/IR switch that senses when someone enters the bathroom and turns on the pump only when someone is in the room. I believe you could use the existing cold water line as a a return line for the pump or if able run a separate line (small pex line?) back to the water heater.
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Old 11-09-2012, 02:13 PM   #46
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Thinking about this some more, I realized that I have been spoiled. People in colder climates need to do the above things to get hot or even warm water. Where I am, the water comes out of the faucet at temperature in the 70F. I do not need hotter water to ensure that my hands and face are clean!

I am going to get out of the bad habit of wasting half-gallon of water to wait for hot water.
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Old 11-09-2012, 02:13 PM   #47
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The heat taken from the hot pipes and into your slab doesn't disappear. It's making your floor warmer and increasing your AC load somewhat. Figure about 2/3 of the "lost" heat is warming the floors and increasing your AC load (the rest is warming the soil under your slab somewhat, being slowly conducted away through that soil). It takes about .3 watts of air conditioning (at typical efficiencies) to remove one watt of heat gain from other sources (your gas hot water heater via this hot pipe). Given the typical difference in cost (per watt) of electricity vs NG, it's likely that, in a climate where cooling is required, a circulating hot water system in the slab is costing about as much in electricity (for AC use) as for NG to heat the water. And then there's the electricity used to run the pump (oh--which also generates heat. Not a factor if it's outside the conditioned envelope).
Okay. I'll admit it, I'm paying a little bit for the convenience of having hot water, virtually on demand. But it is well worth the extra few pennies a month we spend for it. This small cost saves us about 2 minutes per day of waiting for hot water or over 10 hours or so over the course of a year. Also saves us conservatively about 2 gallons of water per day or over 700 gallons per year, water that otherwise would have went down the drain, further increasing my sewage costs based on water usage. Most importantly DW loves it, a happy wife means a happy life.
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Old 11-09-2012, 02:40 PM   #48
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You may be able to install a pump that is operated with a proximity/IR switch that senses when someone enters the bathroom and turns on the pump only when someone is in the room.
How about this idea: Plumb the toilet water supply from the hot water pipe under the sink? Assuming most hot water use in the bathroom is after the toilet flushes, the cool water that is in the hot water pipe would be used to fill the toilet tank and the warm water would arrive at the sink just in time to wash up. No water wasted down the sink drain while you wait for it to get hot, it fills the toilet tank instead.

The two problems:
1) The flow rate through the normal toilet tank valve is less than a sink faucet, so it might take more time for the hot water to arrive (hey, flush and then finish reading that magazine article).
2) A second toilet flush shortly after the first would waste good, hot water.

In some commercial/industrial applications, the heated water going down the drain is used to warm incoming water on the way to the water heater, reducing energy use. In theory, you could accomplish this in your home by winding a copper pipe that feeds the water heater around the large drain pipe from the shower (or dishwasher, etc). It would be impractical for most residences, probably having a payback period of decades.
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Old 11-10-2012, 11:14 AM   #49
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My old house had a really long delay, so we got one of these pumps.

http://www.gothotwater.com/hot-water-pump

Just press a button, wait two minutes, then instant hot water for the shower. Our unit was installed under the kitchen sink, which was the furthest from the heater. IT did return slightly warm water into the cold line, but I didn't need cold water all that often.
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Old 11-10-2012, 11:20 AM   #50
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My old house had a really long delay, so we got one of these pumps.

Recirculating Hot Water Pump - Gothotwater.com

Just press a button, wait two minutes, then instant hot water for the shower. Our unit was installed under the kitchen sink, which was the furthest from the heater. IT did return slightly warm water into the cold line, but I didn't need cold water all that often.
It seems to me that the only real advantage is avoiding wasting the cool water in the hot water line but it doesn't reduce the amount fo time that you need to wait for the hot water to get to the faucet.

In other words, if the concern is time, whether I push a button and wait two minutes for the hot water to get to the faucet or open the hot water spigot and wait the two minutes it doesn't make much of a difference.
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