Check out some similar questions!

homeskillet66 · Apr 4, 2008, 10:57 PM

Thinking of purchasing a DMAND water pump which, supposedly, will bring hot water to my faucet 3-5 times faster than it does now. Right now, it takes about 90 seconds of running the faucet to get hot water to my kitchen sink. Does anybody out there know how well this system works with a tankless water heater?

homeskillet66 · Apr 8, 2008, 12:49 PM

Anyone... anyone... Bueller...

Any thoughts on using a water pump with a tankless water heater... anyone??

ballengerb1 · Apr 8, 2008, 02:16 PM

OK 32 folks have read your post but no answers yet. I think the only folks who can answer this question is the manufacturer of your tankless heater. The DMAND system works by pulling the room temp water out of the hot water line and shoves it back down the cold supply line so you do save water (think green.) However, that may increase the flow rate beyond what the tankless folks spec for your heater. It should work, in theory, but the flow rate is a question I can't handle.

homeskillet66 · Jul 7, 2008, 01:43 PM

Originally Posted by homeskillet66

Thinking of purchasing a DMAND water pump which, supposedly, will bring hot water to my faucet 3-5 times faster than it does now. Right now, it takes about 90 seconds of running the faucet to get hot water to my kitchen sink. Does anybody out there know how well this system works with a tankless water heater?

I installed the Metlund Dmand S-70T water pump under my kitchen sink. When I want hot water, I push a doorbell button which starts the pump, subsequently kicks on the tankless water heater, and brings hot water to the sink. After the pump has kicked off... When I open the faucet, it takes about 5 seconds to get hot water (it used to take 90-100 seconds).
This is a huge water saver and must-have if it takes a long time for you to get hot water. Cost was about $380 plus 1 hour of plumber fees if you don't have the skills to install it.

jlisenbe · Jul 7, 2008, 04:58 PM

It was taking you a minute and a half to get hot water from a tankless water heater? How far away was it?

KISS · Jul 7, 2008, 05:40 PM

I have one. Not installed yet, but for a tank system.

I doubt it would work, but it might if you had a small tank, but you'd have to use it for all hot water taps. The tank just has to be the volume of the pipes with a dip tube and outlet. The Dmand system would have to have enough flow to turn on the tankless heater.

At the furthest tap, th dmand system would be installed as usual between the hot and cold water supplies.

You would start the p.ump, water would flow out of the tankess through the cold water It would do it's thing and then shut off. Now you have instant hot water.

The other solution would be to plump the furthest hot to the cold prior to the tankless water heater.

Same solutions they recommend for non-tankless water heaters. The do recommend 3/4" for the return lines.

Milo Dolezal · Jul 7, 2008, 07:12 PM

We routinely install Hot Water Circulating Pumps in new houses in combination with Tankless Hot Water Heaters. In So.California, there are 3 major tankless w/h brands on market: Takagi, Bosh, and Rinnai.

Rinnai is the best as to compare to the other two brands. Bosh is the worst, especially the AquaStar model with 1/2" water inlet / outlet.

Not every pump can be used. Most Groundfo's, for instance, will not work with certain tankless heaters since it circulates water too slowly for heater to activate flame. We use one specific LAING pump that is made specifically for tankless heaters.

Manufacturer suggests that if you are using hot water circulating pump, that you use hot water storage tank. If you think about it, presence of storage tank defeats the energy saving properties of tankless w/h. In other words, you get rid off of your old tank, that was being re-heated 24/7 - and than in its place - you install storage tank that is constantly being reheated by - now - fancy, tankless heater. It is the same thing.

Kitchen faucet has always had problem with late hot water delivery. Kitchen sink doesn't require lots of hot water in one use, but in many small amounts. What we do, we install 2 to 6 gln elec. "point of use" hot water heater under the cabinet, right below the faucet. The heater is fed with hot water. This way, we don't have to run all the hot water for entire house to the kitchen sink and then back.

Disadvantages are: Hight start up cost, including installation. Can not be always used in the same spot as old, conventional, heater. In many cases, new dedicated gas line has to be installed from gas meter all the way to the heater. Only dedicated vent can be used + venting has certain limitations. Has bit of delay before flame kicks in. Lack of operational history and very few plumbers can troubleshoot it.

Advantages: small, technologically advanced, energy saving unit ( when used w/o pump ), and, of course, continuous hot water for as long as you please.

homeskillet66 · Jul 8, 2008, 08:19 AM

Originally Posted by jlisenbe

It was taking you a minute and a half to get hot water from a tankless water heater? How far away was it?

Yes, 90-100 seconds 'til the water was "hot", not just warm. Distance from tankless to kitchen sink is approximately 50 feet.

Milo Dolezal · Jul 8, 2008, 08:12 PM

I think 1 -1.5 minute hot water delivery is normal, especially when hot water pipe is ran through concrete slab and through 3/4" pipe.

jlisenbe · Jul 8, 2008, 08:55 PM

10 seconds is normal in my house and it is far from new. 90 seconds to get hot water fifty feet sure seems wildly out of line. That would be moving water at about 6 inches per second. Sounds to me like the tankless heater has problems, but I don't claim to know much about them.