Recirc Pump with Takagi Instant H20 Htr

Discussion in 'Pumps and Tanks Well Forum & Blog' started by tobinator, Apr 8, 2005.

  1. tobinator

    tobinator New Member

    Takes over 60 seconds to get hot water at my kitchen sink, so I need to hook up my recirc pump myself since my plumber flaked out on me. I have a old home with all new supply piping including a 1/2 recirc line. Water heater is an instant hot Takagi TKD-20 that requires 3/4 Gallons per minute demand in order to fire. Water heater is located in the basement, recirc line is from upstairs bathrooms on 2nd floor. Total rise from heater to top of recirc riser is about 12'. Plumber planned recirc pump to be located in utility room in basement. Looked at the Grundfos Model UP10-16B5 ATLC. My preference is to locate the pump in the basement utility room. Will this pump work? Will it created 3/4 GPM demand even with a 12' rise from the heater to the end of the recirc run? Takagi manual can be viewed at:

    Thanks, Matt
  2. Gary Slusser

    Gary Slusser That's all folks!

    I don't know much about this but I've not heard of a recirc system on an on demand water heater before. And I'll be damned if I'd feed the electric company enough to pump 3/4 gpm constantly and then fire my demand heater just to not have to wait a minute for hot water! But then I'm an old dude and have tons of patience and wouldn't spend all the extra money for the plumbing, pump and the rest. IOWs, I think it's a dumb idea and possibly not doable. Why didn't the plumber do it?

    Quaity Water Associates
  3. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona

    The height of the water is immaterial for a closed system. The important thing is the friction loss through the piping at the pump's developed velocity. If the pump will activate the flow switch, and it should, then you can install a globe valve after the pump and close it to the point where the flow is just adequate to operate the heater. Just realize, that if the water making the circuit cools down enough, the water heater will never turn off, but will just modulate to a lower firing level.
  4. tobinator

    tobinator New Member

    HJ, the circuit is fairly small. I'd estimate it at about 50' of 1/2" CU. The pump I'm looking at has both an adjustable thermostat and a timer, so I wouldn't be heating all day, probably just early AM and evenings, and then just to 95 degreees for twenty minute intervals during those periods to keep the water warm. The globe valve is already in, so it makes my job a little easier.

    Gary, we are on a well and the incoming water is pretty frigid. So a minute of 45 degree water can seem like a long time. The use of a recirc line is covered in the Takagi (NG Fired) manual, so the concept isn't unheard of. Since the recirc line is already installed, I'd only be adding the pump. Not sure if it's a dumb idea, but maybe we should wait and see if it is really an issue. Perhaps with insulated pipes and pretty regular use of hot H20 during "business" hours, we won't really be waiting. Plumber didn't do it because he is a jerk. He was recommended to me by a friend and he "sold" himself as an expert. He was temporarily laid off from a large HVAC company in Seattle, and he agree to do the job over a two week period. He was borderline incompetant. As an example, he failed to sweat at least 12 connections. Found the last one (hopefully) the day before drywall went in. There were a number of other things as well, that is just the most obvious.
  5. srdenny

    srdenny Plumbing Contractor

    SF Peninsula
  6. carol crom

    carol crom New Member

    Recirculation Pump

    A recirculation pump will work great, and I believe that the hot water saved will more than compensate for the small amount if electricity used. About 7 years ago, I installed radiant heating in our house. It was a lot of work but worth it. While installing the radiant heating, I also installed a recirculation pump for recirculating hot water to all the remote faucets. I installed a Takagi TK 2 for all our hot water needs.

    I use a Grundfos P/N: 59896127 Type UP 15-8-SU recirculation pump. It uses about 80 wattswhen runing. I used 1/2" PEX flexible tubing for the recirculation. Its lots easier to work with than copper tubing. I have a Green Air Products timer which allows setting of both cycle time and duration.

    A check valve is required to keep cold water from flowing backwards through the recirculation system. Be sure to use a high quqlity check valve. Its a good idea to have shut of valves on each side of the check valve to allow cleaning or replacement of the check valve.

    Be sure to have good insulation on your hot water pipes and also the recirculation return. This will reduce the heat loss considerably.

    Taknless water heaters need to be descaled from time to time. The recycle pump can be used ro help with this task and save some money on a descale kit. Plan ahead so you can ues the recirculation pump to ercirculate descaling solution through your heater.

    Good Luck,

  7. Gary Slusser

    Gary Slusser That's all folks!

    If there is enough hardness in the water to cause scaling problems, then you need a water softener. Usually that would be 3-4 gpg or more hardness.
  8. leeteam

    leeteam New Member

    Los Angeles, CA
    Recirculation pump for a tankless water heater

    If you use a timer for a tankless water heater, you will be unpleasantly surprised when you get your gas bill. A timed pump is not the way to go, unless you know exactly when you will turn on the faucet, every day. It will either stay on longer than needed or turn on when you may not need hot water.

    Get a recirculation pump without a timer and thermostat. I like the Bell & Gossett ecocirc.Ā®-high-efficiency-low-lead-brass-ecm-circulator/ Read about it and you will see why I like it. Use a wired or wireless switch with a timed shut-off delay. (CP Electronics MRT16-REM) It can be programmed for a delayed shut-off from 1 second to 2 hours. Set the time period for the time it takes hot water to reach the fixture furthest from the water heater. When you need hot water, press the remote switch. The recirculation pump starts, and stops at the time interval you programmed.

    This set-up will keep wasted electricity or gas to a minimal amount.
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