On Feb 11, 4:09*pm, RBM wrote:
On 2/11/2012 3:10 PM, DerbyDad03 wrote:









On Feb 11, 2:48 pm, *wrote:
On 2/11/2012 2:39 PM, DerbyDad03 wrote:

True or False?

A hot water recirculating pump won't decrease the amount of time it
takes to get hot water to a fixture, it will only eliminate the waste
caused by the water running down the drain.

True, right?

(Another Ask This Old House inspired question)

It eliminates the waste by providing near instant hot water

How?

Here's the situation shown on Ask This Old House:

The homeowner had a tankless water heater installed. It was installed
at the opposite end of the house from the second floor bathroom and
the plumber used 3/4" pipe from the unit to the bathroom. The
homeowner used a stop watch to show that it took a full minute to
drain all of the cold water out of the pipe before there was hot water
at the fixture.

A recirculating pump with a push-button control (and a remote for a
second bathroom) was installed under the bathroom sink.

How would a recirculating pump speed up the emptying of the pipes? It
still has to pull all of the cold water out of the pipes before hot
water could reach the faucet. Does it move the water at a rate much
faster than the normal water pressure in the house can move it? If so,
wouldn't that faster flow rate be too fast for the tankless water
heater to heat it up?

I don't know that one would work with a tankless heater because the
tankless needs flow for the heat to come on. The type of loop I
generally see is connected to a standard hot water tank. It has a bronze
circulator pump controlled by an aquastat. In circulating the hot water
off of the top of the tank, it keeps the entire loop hot

The pump did cause flow since it was pulling water from the pipe
connected to the tankless heater and pushing it down the cold water
pipe.

However, the fact that he installed a button and told her "When you
want hot water, push the button and the pump will come on\" is what
makes me ask the question.

Here's the exact part of the episode that prompted my question:

Before he installed the pump, it took a full minute to get hot water
to the sink. After he installed the pump, he pushed the button and
said "Did you hear the pump turn on?" (homeowner says "Yes") a few
(TV) seconds later he says "OK, now the pump is off." He opened the
faucet and got hot water.

I said to the wife: "BS. It's still going to take a full minute to
empty the pipes. There must have been some hot water in the pipe to
begin with or it wouldn't have gotten to the faucet that quickly."

There was no mention of on/off cycles keeping hot water in the pipes
or a timer or anything like that. Keeping hot water in that length of
3/4 pipe would probably defeat the efficiency gains of using a
tankless heater. OK, maybe not completely, but you see my point.