tankless water heater delay


I was watching this old house and they were installing a tankless water heater. And to over come the delay a recirculating pump. The solution to having the pump run all the time was to install a motion detector in the bathroom which would signal the pump to start.
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What was it recirculating? Cold water?
If it was truly tankless, the idea is not to have the burner or electric coils come on unless you need hot water. There is nothing to keep the water hot for long periods of time when the burner is off. The unit should be installed close enough to the point of use so that the delay is minimized.
Recirculating loops work OK for conventional (tank) systems, although they should be insulated unless you like spending money to heat the interior walls 24/7/365.
Personally, I prefer a conventional system with the design of the hot water heater as close as possible to the critical points of use (bathroom - kitchen, etc.)
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No, the hot water, the pump removes the standing cooled water in the pipes between the tankless heater and the point of use. Of course, it does nothing to deal with the "cold water sandwich".
Cheers, Wayne
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wrote:

TOH is doing a totally "green" renovation is Austin. Something we are all going to have to do someday. We have a drought situation in California now with voluntary conservation being sought and with the cost of energy always going up the tankless heater will be used more and more. Someone a few weeks ago was asking how to deal with the delay of getting hot water I just thought I'd share a solution. It also reduces the cost of running the recirc pump to when someone enters the bathroom.
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On May 2, 12:43 am, snipped-for-privacy@notreal.none (Beachcomber) wrote:

Unless you are going to have multiple units, which is cost and install prohibitive, in many cases in a typical house it's not going to be possible to locate a single unit close enough to all the important use areas. That's why the pump makes sense, just as it does for houses with a conventional water heater.

The system under discussion doesn't circulate water 24/7. It starts the pump when someone enters the bathroom. Other systems use a push button. So, they are not that different in the need for insualtion than a system without the pump.

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Sounds more like a convenience rather than something that is energy efficient. So there is a 5 second delay to your hot water. What's the big deal? The cost of polluted water is still cheap in most areas. Adding a circulation system and the extra copper (or plastic if you like) seems more like a loss in the long run. Not to mention the added price of its repair over the years.
If your house is so large that it takes even longer than that, your going to have to install multiple units because of your water demands cant be handled by only one machine.
Tom

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On May 3, 8:26 am, snipped-for-privacy@gmail.com wrote:

If it was only 5 secs, it wouldn't be much of a deal at all. In fact, even with the pump system under discussion, it's likely still longer than that. However, it's very common to have delays of many times that in a large 2 story house.
The cost of polluted water is still cheap in

The pump systems like the one being discussed go close to the faucet, like under the vanity. The only extra piping is between the cold and hot water lines under the sink.

No different than most other home convenience items.

An upstairs bath in a typical mid range 2 story home commonly takes longer than 5 secs to get hot water. And tankless are available that will deliver 10+ gal a min, which is a lot of water. At that rate, a 50 gal conventional would be gone in 5 mins and you see lots of 3000-4000 sqft homes with only one 50 gal tank. So, you can certainly have a fairly big house with only one unit. However, using 2 units would be an option and could help reduce the delay.

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On 3 May 2007 07:33:31 -0700 snipped-for-privacy@optonline.net wrote:

Using 2 units won't change the delay.
-frank
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Using 2 units will almost always reduce the delay, because the units are then almost always located closer to the faucets. For example, you'd typically have one unit in the basement close to the downstairs baths and then another one upstairs or in the attic, close to the upstairs baths.
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We have a one story house, with the water heater about 40' from our master bath shower.
With low-flow shower heads and 3/4" main supply lines, it takes well over a minute for the hot water to reach the shower head.
Thankfully, I installed a recirculation system when I plumbed our house, which circulates the water to a point just under the shower floor. Even with the recirculation system running, it can take 5-10 seconds for hot water to make the trip from under the floor to the shower head.
Our recirculation pump runs on a timer, so if we take a shower during the usual "off" time, it's a long cold wait for hot water, with a lot of water just going down the drain.
Anthony
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wrote:

If you have a basement, you might be able to use a recirculating thermal siphon instead of a pump. (For possibly less energy and maintenance costs). The idea is that hot water rises because it is less dense and by the time it gets to the top of the riser pipe, it will cool and sink down the recirculating pipe. Of course, good pipe insulation is recommended.
Many multi-story apartments and condos are plumbed this way.
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I already have the pump installed and working well, so I don't have much reason to change it now. Compared to the rest of our energy use, the recirc system doesn't use much.
In any case, I thought thermal systems relied on the water heater being at the bottom of the loop. In other words, the hot water rises from the water heater, up through the pipe, then comes back down the recirc line as it cools on the other end.
Assuming that's the case, we don't have a basement, so the water heater is higher than most of the fixtures using the hot water. And we have vaulted ceilings throughout the house, so we don't have an attic to run the recirc line up through either.
Anthony
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