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Author Topic: How should the routing of the pex go with multiple heat draws  (Read 3908 times)

gandgracing

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How should the routing of the pex go with multiple heat draws
« on: November 03, 2010, 10:53:49 AM »

My hot water from my owb comes up thru the floor to the top of my furnace(it's a downdraft). I need to hook up a flatplate heat exchanger for my dhw. Do I first go to the flatplate and then back to the furnace?  And what if I added a heat exchanger to my garage off the same incoming line?  It seems like somekind of manifold could be used but I didn't see any for 1". And what about the cold return lines?  Can 2 lines come together going back to the stove?
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juddspaintballs

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Re: How should the routing of the pex go with multiple heat draws
« Reply #1 on: November 03, 2010, 03:04:18 PM »

If you don't see a manifold you want from this website, give her a call and have what you want made.  She makes excellent products in a very timely manner.  I'd buy from her again in a heartbeat.

http://outdoorwoodfurnaceinfo.com/forum/index.php?topic=598.0
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willieG

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Re: How should the routing of the pex go with multiple heat draws
« Reply #2 on: November 03, 2010, 08:49:42 PM »

i would suggest a header..store bought or home made (some guys just use galvenized pipe and a bunch of tees with a valve on each outlet. make sure you get one with an extra outlet or two for future use and you can use one of these extras for bleeding your system.
 i use both a feed and return header system. makes it nice for controlling things. like right now i only have my floor heat and domestic water turned on. when it gets cold i turn on my house furnace rads and rads that i have inside my fire place (no more wood fires in the house) and  also i have a rad in my "games" room in the basement.
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Ontario Canada

gandgracing

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Re: How should the routing of the pex go with multiple heat draws
« Reply #3 on: November 04, 2010, 05:27:32 AM »

So should I stick with the 1" or should the header itself be bigger and have 1" coming off of it?  I just kept thinking it should be one continuous line coming in from stove, running thru everything and then back. Will those manifolds cut down on flow quite a bit?  Especially on the return one.
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yoderheating

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Re: How should the routing of the pex go with multiple heat draws
« Reply #4 on: November 04, 2010, 07:33:34 AM »

 I never split the lines before going through a flat plate heat exchanger. The only way you will get a consistent water temp is if you go to it first and then to your other heating needs.
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juddspaintballs

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Re: How should the routing of the pex go with multiple heat draws
« Reply #5 on: November 04, 2010, 11:28:50 AM »

If your PEX lines into your house are 1", I would get manifolds with 1" bodies so you could close down all of your heating "zones" and still flow the entire amount of water through the manifold with no ill effects. 

The reason I went with a supply and return header was for simplicity.  Put your supply header on the end of your supply line somewhere convenient in your basement or such.  Put your return header on the beginning of your return line and somewhere convenient near your supply header.  Connect the two headers with whatever you're heating (for mine I have my water/air exchanger, DHW, and radiator in the basement).  The heat loads receive the hot water from the supply header and return the cooled water to the return header.  This only requires ONE circulator.  If you use a single large manifold with all zones supply and return off of that, you'll need one circulator to circulate the main loop and a small circulator on each loop to circulate water to/from that loop. 

If you do one continuous loop for your whole system, it could cause heating problems.  If you did that with your furnace, flatplate, and garage designed around a 180 degree initial water temp, the temps would drop for each item as you go through it.  Let's say your furnace was setup for a 20 degree delta T.  180 degrees into your furnace, 160 out.  That means 160 degree water into your heat exchanger and maybe 150 out.  That leaves you with 150 degree water to heat your garage and maybe 130 degree water returning to your OWB.  That means your OWB has to heat the water load 50 degrees before it can return to heat your house properly.  With a manifold system, your furnace would draw 180 degree water and return it 160, your flatplate would draw 180 degree and return it 170ish, and your garage would draw 180 and return it 160.  Your OWB only has to raise the temp 20 degrees then.  It would be a larger volume of water to raise 20 degrees, but it's all about the delta T and longer burn times as opposed to short inefficient fires. 
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willieG

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Re: How should the routing of the pex go with multiple heat draws
« Reply #6 on: November 04, 2010, 04:43:18 PM »

my header is 1 inch..my supply from the header to the home furnace is 3/4 frm header to domestic water 3/4 from header to floor heat 1/2 from header to rad in fire place 1/2

same for return header.
you have to remember that your pump on the 1 inch line is delivering only so much water from your OWB to the home (lets say for fun that is 12GPM if all your "applilances" ar calling for heat at the same time y ou will be splitting that 12 GPM up somehow. how that really is i am not sure as it would depend on the line size the line length and resistance in the appliances themselves.

again for fun lets say my home furnace is getting 5 and my domestic water is getting 4 (my lines to these appliances are both 3/4 but my home furnace is closer)  that is 9 of the 12 my pump can deliver. now my other lines are only 1/2 inch so they somehow split the other 3 GPM so at the return line going back to the stove we are still returning 12 GPM and as stated by the fellow above we are sending those 12 GPM back to the stove at the delta  that keep my stove at a good operating temp. Also we muct take into account that most of these "appliances" can deliver the heat load that is needed at much less than the 12 GPM that my stove is deleivering

in fact i have never seen my stove return water temp more than about 10 degrees lower than the stove temp
I do see my stove temp drop as low as 140 and my return will be 135 at that same time as i don't use a side arm or flate plate to keep my hot water tank full. I bypass my hot water tank and use "on demand" coil to heat my hot water, so a long long shower can draw my stove down to "kick in temp" tthat i set at 150 and by teh time the blower gets the fire going and it starts to catch up it can get (the stove) as low as 140

Thats my set up anyway
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gandgracing

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Re: How should the routing of the pex go with multiple heat draws
« Reply #7 on: November 04, 2010, 08:42:09 PM »

Well I'm not worried about putting a heater in the garage anytime soon so I need to just get this flatplate hooked up. Could I make a supply and return manifold out of 1" pex T fittings with 3/4" coming off the T and going to the furnace and flatplat. I'm just wandering if it will change swithing 1" to 3/4" going to the furnace.
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