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Thread: Open system idea - thoughts?

  1. #1
    DIY Junior Member BDrivenByDemons's Avatar
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    Default Open system idea - thoughts?

    I have a 2400 sqft ranch with a full basement. I've been kicking around the idea of putting some radiant pex loops under the bathrooms cause the tile gets so cold. I'm also kind of an efficiency weirdo and have been trying to come up with a way to minimize the amount of pumps and loops I would need. I know I can zone and valve but that adds to cost/design. So I had an idea...

    I also wanted to set up a hot water circulator loop since many faucets are far from the heaters and it takes a while to get cold water. I'm thinking I could make one big 3/4" loop that would circulate constantly for instant hot water at the faucets. Then where I need heat in the winter I could tee a parallel pex loop into that big loop using some kind of actuated diverter valve. The main loop would always be pumping hot water. I get a call for heat at one zone and the valve would redirect flow through my small pex loop till heat was satisfied then go back to the main loop. Only one pump needed for two purposes. Any thoughts? I know I'd need to use bigger pex since fixtures may call for water during a heat cycle and I'd want good flow but so what? I'd also need some way to periodically switch loops for a short time in the summer to prevent stagnation but I could figure that out with some cheap timers.

    Looking forward to comments as I feel like this could work really nicely and with a minimum of equipment.

  2. #2
    DIY Junior Member Raspy's Avatar
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    By the time you size the recirc loop and route the recirc loop to do heating as well as recirc, and then install a control system, you might just as well dedicate a heating loop with it's own circulator. It seems you might be adding too much complexity only to avoid using another circulator.

    If you propose putting the heating loops in the joist bay space then the temp required is about the same as the recirc temp. So maybe you can avoid the diverters and simply let the recirc heat the floor. Of course, you'd have heat when you wanted hot water and you'd have it all year, but that might be fine. Heating tile from joist bay tubing is slow and requires a higher temp than tubing in a mortar bed or thin slab.

  3. #3
    DIY Junior Member BDrivenByDemons's Avatar
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    Quote Originally Posted by Raspy View Post
    By the time you size the recirc loop and route the recirc loop to do heating as well as recirc, and then install a control system, you might just as well dedicate a heating loop with it's own circulator. It seems you might be adding too much complexity only to avoid using another circulator.

    If you propose putting the heating loops in the joist bay space then the temp required is about the same as the recirc temp. So maybe you can avoid the diverters and simply let the recirc heat the floor. Of course, you'd have heat when you wanted hot water and you'd have it all year, but that might be fine. Heating tile from joist bay tubing is slow and requires a higher temp than tubing in a mortar bed or thin slab.
    I had the same thoughts as you but the loops are so small and it's hard to justify placing pumps by my heat source, running 40' of tubing just to get to the space I want to heat, making a small loop, then running 40' back. AND doing that 2 or 3 times. I feel like my original post makes it simpler. I wouldn't really need a control system the way I figure. Just a transformer and thermostat to open the valves at each heating loop. The main circulation loop to eliminate the cold water at faucets is happening either way so any work involved with that shouldn't be considered. I wish I could draw a diagram of my thoughts somehow. I need a little CAD program.

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    DIY Junior Member Raspy's Avatar
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    I think, for ultimate simplicity, I'd just run the recirc as the heating line. Then valve it later if you can't get the two functions to match with timing and flow adjustments.

  5. #5
    DIY Junior Member BDrivenByDemons's Avatar
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    Quote Originally Posted by Raspy View Post
    I think, for ultimate simplicity, I'd just run the recirc as the heating line. Then valve it later if you can't get the two functions to match with timing and flow adjustments.
    I like this thinking. Manual diverter valves would be perfect for this setup. Now how can I make a diverter valve not close off either section completely? I'm asking to prevent stagnation in either loop. Once installed *I* would know how to operate this setup but I like to make everything foolproof. If I sold the house or something I'd put some simple labels on the valves for "heat" and "no heat" but optimally a very very small flow would be present in either loop with the valve in either position. Is there an easy way to do that? Limits on a valve somehow?

  6. #6
    In the trades Dana's Avatar
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    "Open" systems that use potable hot water as the heating water are a bad idea in general, and even illegal in many states. In MA they are legal only if one guarantees that whether there is a heat load or not, a specified minimum amount of circulation injecting fresh water occurs daily on the heating loop to guarantee you don't have stagnation issues. Most use a duty-cycler timer than runs independently of thermostatic control to achieve that function, but that does induce a small cooling load during the off season if using a recirc system off the hot water heater.

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