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Author Topic: Plate size for in floor heat  (Read 10294 times)

justinb

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Plate size for in floor heat
« on: December 19, 2017, 04:42:22 PM »

Ive been wanting to hook up the in floor heat in my garage for a few years, but never got around to it.  I decided to treat myself and hire a professional.  I got home today to see what was done, and Im concerned about the heat plate exchanger.  Its very small ( about the size of my hand).  The plate exchanger that I installed for my dhw was a large 30 plate.  Did I go overkill, or did this guy undersize my garage??

This garage loop is coming from the return line and will heat a 4 car garage.  Any thoughts?  Ill call them tomorrow, but wanted to check with you guys first.
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justinb

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Re: Plate size for in floor heat
« Reply #1 on: December 19, 2017, 05:31:18 PM »

If it helps...this plate exchanger is rated for 45000btu and measures 3.5"x 8".  It is a weill-mclain wmbp1-14e.
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fireboss

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Re: Plate size for in floor heat
« Reply #2 on: December 19, 2017, 06:19:22 PM »

I heated my pool with a 10 flat plate exchanger with no problem. I can’t remember how many gallons, but it’s an above ground and it’s 24 foot round. I am sure you will be fine   
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E Yoder

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Re: Plate size for in floor heat
« Reply #3 on: December 19, 2017, 08:32:29 PM »

Would need to know more about your system to know for sure. How many and what size loops in the floor, what temp is the water mixed down to, what size piping on the main stove loop and how long, what is it pumping through, etc.
It may be fine.
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E Yoder

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Re: Plate size for in floor heat
« Reply #4 on: December 19, 2017, 08:34:20 PM »

The 45,000 BTU rating can vary dramatically in real life depending on flow rates and water temps.
Is the plate exchanger plumbed directly into the main loop return line? Restriction on that would be my greatest concern if it's a 14 plate, judging by the number you gave.
« Last Edit: December 19, 2017, 08:51:40 PM by E Yoder »
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wreckit87

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Re: Plate size for in floor heat
« Reply #5 on: December 20, 2017, 09:25:34 AM »

By "4 car garage", I will assume that this garage is of fairly considerable size. Perhaps 1200+ sq ft? I'm afraid you won't be happy with that little fella. I run a 20 plate 3x8 on my snowmelt which is only a single loop and does a really good job for what it is, but a building of that size would flatten it in a hurry. In my business, I would install a minimum of a 20 plate 5x12 for a 1200 sq ft building and have recently done so with 130 degree output temps from a 180 degree boiler loop. I'd be interested to see just what that little guy could do, but I wouldn't risk it over $120 for a 20 or 30 plate 5x12 if it were mine
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RSI

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Re: Plate size for in floor heat
« Reply #6 on: December 20, 2017, 05:34:39 PM »

Was this put is series with the main loop? If so I would me more concerned if you are still getting enough flow on the rest of the system.
If the return temps are still about the same under load as before then then small HX may take all the remaining heat you want to pull off the water before it goes back to the stove.

Having more heat transfer doesn't do any good if there is not enough heat available.
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E Yoder

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Re: Plate size for in floor heat
« Reply #7 on: December 20, 2017, 05:46:48 PM »

That's what I meant by more details about the rest of the system. I'm less concerned about transferring heat to low temp garage floor water as I am a small 14 plate slowing flow on the main loop. That affects the garage and everything else.
Anyway, keep us posted how it works.
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Smokeless

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Re: Plate size for in floor heat
« Reply #8 on: December 21, 2017, 06:34:02 AM »

flow is one factor for the boiler. Another is return temp. Keep it above 140 deg F  if you can. Not sure the brand ofboiler you have. Some fail because of cool return temp.
 I always over size any heat exchanger I install because eventually the will all plug up. House side or wood furnace  side. Just gives you more time between cleanings.
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Jon_E

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Re: Plate size for in floor heat
« Reply #9 on: December 21, 2017, 08:09:55 AM »

Reading this thread with some interest as I am going to be hooking up my own garage to my boiler next week.  I have the garage on a dedicated loop from the boiler, 160' away (320' round trip).  The garage will be a closed zone loop so I am using a very small HX (10-plate, 3x8) to get the heat into the zone loop, and then using a 105° to 115° mixing valve to get the zone temperature down to a reasonable level.  I do not want or need my garage to be over 65° during the heating season.  I am heating 800 sf of well-insulated slab, with 3 loops @ 300' each of 1/2" pex at 12" o.c.
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wreckit87

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Re: Plate size for in floor heat
« Reply #10 on: December 21, 2017, 08:59:34 AM »

Reading this thread with some interest as I am going to be hooking up my own garage to my boiler next week.  I have the garage on a dedicated loop from the boiler, 160' away (320' round trip).  The garage will be a closed zone loop so I am using a very small HX (10-plate, 3x8) to get the heat into the zone loop, and then using a 105° to 115° mixing valve to get the zone temperature down to a reasonable level.  I do not want or need my garage to be over 65° during the heating season.  I am heating 800 sf of well-insulated slab, with 3 loops @ 300' each of 1/2" pex at 12" o.c.

How will you be tying that into the boiler loop? That's a REALLY small plate for that size load. I just did a 3 loop floor like yours using a 20 plate 5x12 and was cutting it closer than I'd like with 160 boiler water. Did another 7 loop with the same 20 plate 6 weeks ago that did very well but was running 180 boiler water. There is a 20 plate 3x8 on my snowmelt loop that works well but it's only 160 ft, where yours is 900 with half the exchanger. Scary
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E Yoder

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Re: Plate size for in floor heat
« Reply #11 on: December 21, 2017, 02:01:30 PM »

https://www.weil-mclain.com/products/brazed-plate-heat-exchangers

This link has a brochure for the 14 plate mentioned earlier. In the brochure it appears like a small one can work if (big if) it's on a dedicated secondary loop where you can slap a lot of water through it. Definitely not ideal, and upsizing to one with more plates isn't terribly difficult.  Tied directly into a primary loop the pressure drop is plenty high with only 14. It doesn't cost much more to go with more plates.
I use quite a few 3x8" 30 plates for DHW on basic primary loops in the 4-6 GPM range, but those extra plates reduce the pressure drop a lot.

Jon_E, there are some pretty cheap 3x8 30 plates on ebay if you wanted to size up a bit. Saw one for $65.
« Last Edit: December 21, 2017, 02:26:55 PM by E Yoder »
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Jon_E

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Re: Plate size for in floor heat
« Reply #12 on: December 22, 2017, 09:08:30 AM »

I'm willing to take the risk at this point, since the plate ex was really cheap (lightly used).  Very limited budget and I can always up-size the plate if I need to.   A friend of mine has offered me a much larger plate exchanger (also free) but I am not sure what exact size it is - if memory serves it is something like a 40- or 50- plate exchanger.  Meant for a large coal boiler but never used.  I was thinking that is way too big, so I was going to trial the small one and see how well it worked.  I am not after a lot of heat - just bringing a slab up to temperature and then holding it there. 

Just for comparison, my main house circulation loop is fed by a Taco TFP5X12-30 (self-explanatory, there) and that handles (11) 300' 1/2" PEX loops and all of our domestic hot water with no issues at all.  Great recovery time. 
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E Yoder

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Re: Plate size for in floor heat
« Reply #13 on: December 22, 2017, 10:13:04 AM »

Hey, give it a shot. Plumb it with unions or Pex so you can do an easy swap if needed. Post back how it works, temps in and out on both sides.
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wreckit87

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Re: Plate size for in floor heat
« Reply #14 on: December 23, 2017, 08:56:43 AM »

There is no such thing as "too big" on a plate exchanger. That 40 or 50 plate would do ya more favors than the little 14 plate even for a price, but can't beat free! I certainly wouldn't waste my time with the little guy if that was an option, but I would be interested to hear how it goes if you decide to use the little one.

Am I seeing correctly that you're using the same exchanger to serve you domestic water as well as your radiant floors in the house??? Good luck with that Legionaire's disease
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