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Thread: Selecting Domestic Hot Water Recirc Pump - Tankless - no dedicated return line

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  1. #1

    Default Selecting Domestic Hot Water Recirc Pump - Tankless - no dedicated return line

    Hi,

    Looking for a little help selecting a pump to drive domestic hot water recirculation in my home (I am the home owner). I have a tankless hot water heater and no-dedicated return line. I don't have power available under the furthest two sinks!

    As far as I can tell none of the systems on the market will help me... requiring either a dedicated return line or power under the furthest sinks.

    So I got to wondering...

    What if I use the "return" values from Amstrong's new Astro Express System (looks much more well constructed than the grundfos comfort valves.) These valves create a return path for the water from the hot to the cold pipes at the furthest two sinks - but don't require power.

    Then get a suitably sized pump to trigger the tankless water heaters - which I would mount near the tankless heater in the mechanical room.


    So the question is what pump to buy...

    I see from the Laing ACT-909 model designed for tankless applications, without a dedicated return but mounted under the furthest sink has a head of just over 25ft and max flow of 8.5GPM.

    So what I think I need to try (yes I recognize this is an experiment and it may fail!) is a "simple" pump (no timer, no temp sensor, no check valve - all of which the Laing ACT-909 has) with the following specs:

    - 25ft of head
    - max flow of 8.5GPM
    - 3/4" connections
    - Thermally protected (in case the pump ends up dead-heading against the closed Astro valve... I plan to only turn the pump on* for just long enough to get hot water to the faucets)

    Can some one give me a part number for a Laing, Armstrong or Grundfos pump which would meet these specifications?

    Also... should I mount the pump before the tankless (on the cold water inlet - i.e. the pump is pushing water into the tankless) or after the tankless on the hot side - i.e. the pump is pulling water into the tankless)...or doesn't it matter?

    Thanks

    * I will be controlling the pump using a computer controlled timer I already have (actually an X10 control system).

  2. #2
    General Engineering Contractor ballvalve's Avatar
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    Its stuff like this that makes the world hate America's excessive energy usage. A European would fill their watering can with the cold flow if he REALLY needed hot water to tinkle his hands under. The rest of the world is thrilled to have a mud puddle with a duck sitting in it to wash up in. Most of the earths houses are not 5 or 8000 square feet for a few people, with 25 peaks and valleys in the roof.

    If you insist, wasting the cold water in the drain is likely more cost effective than all the hardware and heat loss. And/or, spend a month in a village in India - you'll be much more patient waiting for that hot water to arrive....

  3. #3

    Default Impact of Water + Gas Use vs. Purchase and Install of Pump

    Quote Originally Posted by ballvalve View Post
    Its stuff like this that makes the world hate America's excessive energy usage.
    If you insist, wasting the cold water in the drain is likely more cost effective than all the hardware and heat loss.
    If you can let me know how you did the calculation to reach that conclusion I'd be interested:

    Option 1: Running water for 3 minutes for each shower, dishwasher run, etc. etc. - plus the gas usage with the on-demand boiler firing at max rate (150,000 BTU) every day 340 days a year
    vs.
    Option 2: No wasted water, running the recirc pump, having the boiler fire at a lower rate on average, but then of course we have to factor in the "impact" of the manufacture, shipping, installation, and end of life of the pump and valves.

    You might be right that the energy used to extract the raw materials, make the pump, ship it, install it and deal with it at end of life could be more than the water / gas wasted without it... but that's a damm complicated calculation.


    The rest of the world is thrilled to have a mud puddle with a duck sitting in it to wash up in. Most of the earths houses are not 5 or 8000 square feet for a few people, with 25 peaks and valleys in the roof.
    And/or, spend a month in a village in India - you'll be much more patient waiting for that hot water to arrive....
    If you feel that on principle we in the West shouldn't have hot showers, dish washers, etc. then that's a totally different discussion - one I'd be interested in having a debate about. I agree with you that the inequity is clearly something that is morally justifyable - and from this perspective my "need" for solving this problem is clearly trivial and inconsiquential.

    BTW just to check your illusions that somehow I must live in a McMansion: my house is a row house, 1800 square feet, built in 1920, with a single pitch to the roof and no valleys, and has been very insulated well beyond current code.

    Also I have a passive drain water heat recovery heat exchanger which pre-heats the cold water (which in my town is cold) using the waste water from the stack

    A European would fill their watering can with the cold flow if he REALLY needed hot water to tinkle his hands under.
    BTW...I'm not American - I'm a Canadian originally from the UK... and I don't own a car.

    Thanks for sharing your thoughts...

  4. #4
    General Engineering Contractor ballvalve's Avatar
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    I was wondering why you let me get away with that reply for so long....

    Well, okay, if you have a single roof pitch in an old house, you pick up some waste heat from the drains, and you don't have a car, you have at the very least mitigated out the carbon footprint of your desire for instant hot water. Probably more so. Personally, I would forgo hot water altogether rather than not have a car, but then where I live, a bus or trolley is only found under a large tree and used as a living space for those Americans that make living in a backwater Afghan village look inviting.

    "Thrift" in America is becoming a fairly lost adage, and indeed it is hard to get that watering can under those short sink faucets if in fact you have plants and wish to use that run of cold pipe water to keep them green... I dont think we have enough wine or spirits in stock to start a debate about the life cycle costs of the recirc pump and gas consumption.

    I know a few folks that have learned to turn on the "hot" water to brush their teeth and wash their hands with while getting ready for a shower. We don't need a lot of alcohol to agree that system is economical.

    And I suppose your recirculation system, if on a timer for main use times, and especially if only in the winter, would be fairly neutral in costs - assuming the waste heat is warming the cold house.

    Because I have radiant heat, my problem is reversed during the winter when I want COLD water - everything comes out hot.

    Main point, when every Chinese, Indian, African and Indonesian takes up golf and wants an instant hot shower, you might just as well bite down on that cyanide tablet than wait for the nuclear bombs to start falling.

    Have you seen this months National Geographic dedicated to water? Sums it all up nicely.

    Around here, whole rows of those styrofoam-stucco faux vomit "spanish" Mcmansions sit empty, bank owned, bold testimony to the greed of mortage brokers that would lend to your parakeet a few years ago.

    As lemmings, I think our cliff is in sight. Cheers, until that day!

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    In the Trades Wally Hays's Avatar
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    Let's bypass the energy stuff for a bit and get back to the problem. You said you have a tankless heater. I assume you mean like a rinnai or Noritz type heater? If so you can not use a re-circ line because they void the warranty on the heater.
    Perception is 3/4 of reality

  6. #6
    General Engineering Contractor ballvalve's Avatar
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    Looks like you gotta go green anyway!

  7. #7

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    No, I am not concerned about the warranty - the unit is more than 5 years old now anyhow.

    But I can't open my walls to put in a dedicated recirc line, and I don't have power under the furthest sink - so the Lang ACT-909 and Chillipepper solutions won't work for me.

    I did talk to Laing about my idea (see first post) of using their UCT-909 Astro Express valves (similar to the Grundfos comfort system valves) with a pump of the same size as the ACT-909. But they said it won't work - because the flow rate through the valve is very low. While I can trigger the boiler based on the pump timer rather than flow rate the Laing technician suggested that having the UCT-909 trying to force water through the low flow valve would not be good.

    BTW I was also told by both Laing and Chilipepper that they are working on a solution to my problem - obviously enough people are in the same situation as me: installed tankless heaters without return lines and without power under the sink and then realized they'd reallly like a recirc system! Laing thought it would be 9 months before their system was launched. No timeline from Chilipepper.

    In the mean time if anyone has any other thoughts on how to do this I'd be interested.

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    Shared Well Services RayMan's Avatar
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  9. #9
    General Engineering Contractor ballvalve's Avatar
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    Surplus center is a great place but they dont have a pump for this silly use. Try Graingers for Grundfos, but 25' of head is an expensive pump with a wet rotor and mag drive.

  10. #10
    DIY Junior Member too old for this's Avatar
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    I never saw such harsh replies until i joined. Sheesh!
    Grainger or *******. I recently saw recirc pumps (Grundfos) in *******, but didn't catch the specs. 25' of head is a lot! I have limited experience with hydronic heating, but if you keep the air out of the lines, which you would with potable water... you can get by with less head. The water that falls down the cold pipe will pull up or balance the force in the hot pipe going up. Make sense? A check valve under the farthest sinks H > C should do it. Put the pump on the cold line going into the tankless. The pump will last longer. Make sure you get enough flow to trigger the tankless. Some of those require quite a bit due to the BTU rating. It's your house. Do what you want!

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    DIY Junior Member too old for this's Avatar
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    The store name got blanked out. Save big money at M...... You know. the guy that was into indy car racing that owns all those indoor lumberyards in the midwest.

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