Selecting Domestic Hot Water Recirc Pump - Tankless - no dedicated return line
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?
* I will be controlling the pump using a computer controlled timer I already have (actually an X10 control system).
Impact of Water + Gas Use vs. Purchase and Install of Pump
Originally Posted by ballvalve
If you can let me know how you did the calculation to reach that conclusion I'd be interested:
If you insist, wasting the cold water in the drain is likely more cost effective than all the hardware and heat loss.
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
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.
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.
And/or, spend a month in a village in India - you'll be much more patient waiting for that hot water to arrive....
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
BTW...I'm not American - I'm a Canadian originally from the UK... and I don't own a car.
A European would fill their watering can with the cold flow if he REALLY needed hot water to tinkle his hands under.
Thanks for sharing your thoughts...