May or may not be accurate. But, there is one major flaw. By running his tests only at night, he did not take into account the energy wasted by having to run the water longer at each faucet in order to get hot water. That would have to be accomplish by measuring flow rates at each faucet and timing how long it takes to get hot water and keeping track of how many times per day each faucet is run. Then he could determine total gallons wasted, calculate energy costs and water costs and subtract that from his $$ to see if the recirc system cost or saved money. His initial calculations only tell half the story.

in my case it would be a waste because my lines are installed underground and not insulated. therefor if i don't have a flow rate of at least 3 galls a minute my water never gets hot.

Of course he failed to consider the cost ($ and energy) of wasting water while waiting for it to warm up.

As for the basic premise, of course it costs money ($ & energy).
Maybe he should get rid of his electric service and go back to manually pumping his water.
And propane is a very expensive way to heat.
He should switch to a decent wood burning fireplace, and be sure to fell and cut the wood by hand.

If he lives in a deep enough cave the earth temperature starts to go up, so he could avoid heating and cooling costs altogether.

Convenience costs money.

While I didn't really go through the OP's number carefully, they all seem to be based on the most pessimistic assumptions possible.

I'm pretty sure the hot water circulation system in my house (Grundfos UP 10-16) saves money because I don't have to waste hundreds of gallons of water every year waiting for hot water to arrive at any of the showers or faucets throughout my house. Not only do I save water, but since my sewer tax (which is about double the cost of water) is based on water usage, I save again when I don't need to run water needlessly.

The circulation system in my house is controlled by a timer AND an aquastat. That means it runs only during the hours that hot water would be in use (not 24/7), and it shuts off when the sensor in the aquastat detects that hot water is present throughout the system. I'd guess the pump is running only a few minutes every hour, and doesn't run at all during the night.

Even if it doesn't save money (I haven't run any numbers), I'm sure the cost to run the system is nominal compared to the comfort and convenience it provides.

"Convenience costs money."

Pretty much says it all....for just about every topic.

You don't need any "figures" to determine that a recirculating systems wastes energy - it's keeping more water hot all the time, and it's keeping it in un- or maginally- insulated copper pipes. I can't imagine a situation where it wouldn't use more energy.

That being said, WOULD be nice not to have to wait...

My strategy for minimizing the wait is placing the tank as close as possible to usage, and using 1/2" pipe (rather than 3/4") for hot water supply lines. If you get too many things using it at once, you may have a flow issue, but you're probably going to run out of hot water anyway...

I am currently re plumbing my master bath. My plan is to run a recirculating loop back to the water heater with a pump at the heater, which will be controlled by an aquastat in conjunction with a switched power supply, which will be switched on when the bathroom light is switched on.

My recirc pump is activated by a motion sensor along with one of the bath fans.

Now I never forget!

The recirc system uses energy and of course costs money - but if the DW says she can't stand waitng around for hot water to flow - it's worth every penny you spend.

The cost to run my 30 watt recirc pump is pennies per day (the max cost per kilowatt hour in my region is 2.3 cents!) The cost to heat the water with my 4 gallon tank is about 25 cents per day.

This all comes out to about a little over 100 bucks per year minus the cost savings of not running the tankless system for 5 minutes eveytime I need a little hot water to flow. I think I might be saving money - not wasting it.

But I am not going to calculate it - the DW is happy and so whatever it costs, or saves, it's worth it!

I had a recirculation pump with a dedicated return line and a timer but it had two problems:
1) Most of the time the pump is running, it is not needed
2) when Hot water is needed, the pump is often not running.

I solved the problem with a unique "on-demand" control that turns on the pump when the hot water anywhere in the house is turned on.

You can see a diagram of the set-up at:

http://i480.photobucket.com/albums/rr167/PRYGAARD/RecirculationControl.png[/IMG]

1) On the cold water IN on the Hot Water tank, a flow switch is installed that turns on when it detects flow. (Note: This can *not* be anywhere in the circulation loop)

2. A Delay-Off timer turns the pump on immediately when the Flow Switch turns on, but does not turn off the pump for a while after the flow switch is turned off. (The delay time needs to be adjusted for the characteristics of the particular installation. Typical times range from 30-90 seconds)

3) An aquastat is used to turn off the pump when the farthest faucet in the loop reaches temp.

When the hot water is turned on, the pump comes on and hot water arrives very quickly (but not instantly). The innovation is this: Turn the hot water on for a second and then turn it back off...and the pump keeps going for a while. Then just wait for a little bit and turn the Hot water back on...it is hot and ready to use. After the water is turned off, the pump will run for the delay time and then stops till the next time there is demand.

Flow Switch: Gems 26605 (I got it cheap on ebay). (http://www.gemssensors.com/ApplicationSearchResults.asp?nQuestionID=36 ) Others are available, but be sure to get one that has a fairly low trip point on the flow. (.75 Â 1 GPM)

Delay off Timer: MX046 timer kit. (15 second to 6 min delay)
(http://www.bakatronics.com/shop/item.aspx?itemid=466) It is inexpensive but you must build it into a case. There are other delay-off timers and relays available but this seems to be the cheapest option.

Aquastat: Grundfos ½" Clip on.

I goofed the URL for the image of the system I described above. The correct URL is:

http://i480.photobucket.com/albums/rr167/PRYGAARD/RecirculationControl.png

(The [/IMG] was removed) Sorry for any confusion.

I have a similar installation in my house.

Setup:

- Two second story baths fed from the same PEX manifold.
- One 1/2" hot water return line
- Without recirc, about 60 seconds for hot water to make it to taps.

Solution:

In basement, we have a Grundfos recirc pump. Pump has thermostat and timer, though the timer is not used. In the two baths, I installed motion detectors.

When either detector is triggered, the outlet for the pump is powered for 20 minutes. When the pump is powered, it is controlled by its thermostat. After 20 minutes of no movement, power is removed from the outlet.

Since we almost never go into those rooms and immediately turn on the hot water, by the time we need it, the loop has been charged and it takes less than 10 seconds for hot water to come out.

I ran the recirc for almost a year before putting in the detectors and I can tell you that any energy usage difference now is imperceptible versus when we did not have the loop. In contrast, the water heater used about twice the amount of energy when the recirc had only thermostat control.

The detectors were about $10-15 each and the timer (Honeywell HPT6062) was $25.

I really like both of these setups. The motion detector uses inexpensive off the shelf parts (Lowes)and gets the water hot before it's needed but without wasting the heat when it isn't needed.

The flow switch has the potential to have all of the electrical right by the pump, thereby avoiding running wires to the bathrooms.

prygaard - Do you even need the aquastat? Or could you put the aquastat on the return line near the pump? The idea would be to not have to run the line for the aquastat.

Also, the flow switch you used wasn't showing up on the website... can you suggest a different one?

Or you could engineer your recirc system that would not require any pump, switches or flamshatter valves. Clue: elevation, elavation, elavation.

Or you could engineer your recirc system that would not require any pump, switches or flamshatter valves. Clue: elevation, elavation, elavation.

If you are talking about a gravity loop, the amount of operating energy they waste is worse than any up-front savings on materials.

TO Jake2007
Sorry about the delay I have been away on vacation.

> "Do you even need the aquastat? Or could you put the aquastat on the return line near the pump? "

The aquastat only really kicks in when we are using hot water for an extended time....but you are correct, since the pump only runs when we use hot water, the savings probably are not huge. And yes, you could put the aquastat at the pump and get most of the savings without running the wires.

> "the flow switch you used wasn't showing up on the website..."

Ooops sorryÂ. I had a typo. I used the 26615

Others that would work are:
27051 - FS-200 Series - Straight-Through Flow Path, 1" NPT Ports, 0.5 GPM

27052 - FS-200 Series - Straight-Through Flow Path, 1" NPT Ports, 1.0 GPM

26440 - FS-400 Series - 90° FlowPath, 1" NPT Ports, .75 GPM

26600 - FS-400 Series Adjustable - 90° Flow Path, 0.75" NPT Ports, 0.75 to 4.0 GPM Range

26615 - FS-200 Series Adjustable - Straight-Through Flow Path, 1" NPT Ports, 1.0 to 6.0 GPM Range

(You might want to measure your flow rate by timing how long it takes to fill a quart pitcher)

I would have used the 26440 or 26600 because it would have been easier to plumb but I got the 26615 cheap (and I am all about keeping the cost down on my projects :-) )

Cheers
Paul

Another flow switch that would probably work is the McDonnell & Miller FS6-3/4 high sensitivity or FS6-1 high sensitivity switches:

http://www.mcdonnellmiller.com/Literature/FlowSwitch.pdf
(I just saw one of these cheep on e-bay)

I was asked for pictures of the set-up on a different forum... I thought I would post them here too.

Top of WH and Flow Switch plumbing:
http://i480.photobucket.com/albums/rr167/PRYGAARD/flow-switch-pic-1.jpg

Controller:
http://i480.photobucket.com/albums/rr167/PRYGAARD/Controller-pic-1.jpg

Inside of Controller:
http://i480.photobucket.com/albums/rr167/PRYGAARD/Controller-pic-2.jpg

Enjoy
P

Here is a link that might be useful: