OWF Floor Joist Pex Radient Install

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hedgecutter

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I currently heat my 2600 sq ft house with a Shaver 165 using a 22"X22" three pass HX in my forced air system. The system is controlled with a simple two wire wall T-stat wired to a relay which pulls in the blower and water circulation pump when the T-stat calls for heat. The system works fine, except that my 1st floor, which is 900 sq ft, does not get very good air flow from the duct work. My house is a 1930's farm house with extensive remodeling except for the duct work. Any how, I am planning on installing radiant pex between the floor joists under the 1st floor. I have a full basement so easy access. The plan is to plumb into the OWF water to the new radiant pex header and loops to heat the first floor. I have limited knowledge on radiant pex heating so I am seeking your advice.

1. What size pex to use? 1/2? 3/4? 7/8? How far to space apart the lines?

2. Is is OK to plumb OWF water directly into the radiant pex or do I need to use a water-to-water HX?

3. What is the ideal or max loop length on the pex loops?

4. What is the max water temp I can run through the radiant pex which will be up next to my sub floor? I plan on using a "Temp Mixing Valve" plumbed from the return header to the supply header to control water temp.

5. Should I use the aluminum heat diffusion plates to hang the radiant pex in?

6. Planning on using a water pump tied to a fan control center and wall T-stat to control system. Does that sound reasonable?

And and all suggestions are appreciated
 
1. 1/2" is fine. Assuming floor joists are 16" OC, a single loop between each should be adequate. It also depends on what floor covering, if any, is present.

2. You can use the boiler water in the PEX, however, a separate circulator is suggested as is a mixing valve and zone valving as needed.

3. 250' total is a good length for each loop.

4. 140F is a good starting point - raise or lower as needed.

5. They're more expensive and can be noisy. A simple staple-up to the subfloor with radiant insulation below an air gap will work as well.

6. Probably. Would need to see a schematic of the system.

Steve
 
1. 1/2" 2 per joist, if you can fit them.

2. yes, no HX unless your boiler overflow is lower than the highest point of your radiant, you'll need either a HX, or some back flow prevention valves

3. 250ft

4. 115*-160*, start low and work your way up. if you have carpet you'll need a higher temp.

5. not at first, they are expensive. Use refletive insulation like solarguard, and then pul your batting back in under it. If you have a problem in the future you can always add the plates easy enough.

6. Are you still going to use hydro-air on the first floor, or are you going to block of the ducts? I'd run the radiant on a separate zone regardless. If you want to use both systems to heat the first floor try using a slab sensor on the floor, that way your floor heat won't cycle off too soon.

Depending on how easy it is to close your ducts on the first floor I'd add a second thermostat. 1st floor thermostat would turn radiant pump on to heat the main floor, 2nd floor thermostat would turn on hydro air blower to heat 2nd floor. Both floors would be nice and comfy and independently controlled.

Radient heat is very efficient. I have both floors of my house heated with it, my basement, and my garage. Let me know if you have any questions, I can take pictures of my set up if you'd like.
 
I love my radiant heat! you will too. the first time you take a trip to the head in the middle of the night with bare feet it will put a smile on your face. I guarantee!
 
I first need to make it clear that I'm not a plumber or HVAC expert.

I totally winged it on my set up.

I have the hot water coming in from my Shaver 165 to my HX in the duct work. From there it comes out to run through the radiant heating in a 24'x30' living room. I have no HX for this radiant floor. The pex runs two lines between each joist.

I went with 1/2 pex. I have a Taco 007 in line for a booster pump. I made two 20' long manifolds out of 1" copper pipe. I put five nipples on each spaced about 4' apart. One for out flow and one for return.

I have a 160' run of 1/2 pex on each nipple.

I also made my own aluminum heat transfer plates for the pex between the joists. I bought two 50' rolls of aluminum flashing. I took them to a machine shop to have them chop them into 6" sections. I had a friend, that made a jig, that fit on his log splitter, to make the groove in the flashing for the pex to fit.

I then stapled foil/bubble insulation over the joists.

I don't have a fancy mixing valve, just a ball valve that I never use.

After water flows through manifolds it returns to the OWB.

We have carpeted floor and I run the water temp at 155* on the OWB, although I've heard that water temp is probably actually 20* higher.

Like I said I'm not expert and I totally winged it with my set up but it works and works well.
 
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Thank you for your feedback guys. Now I have a direction to get started in. Looks like I need to head down to the local supply house and start gathering parts to get started. One more question. WindWalker7 commented that he tied into his OWF stream at the outlet of the duct work HX and that is working well for him. I was planning on tapping into mine just prior to the inlet to my duct work HX. Other than a difference in water temp, do you see any thing wrong with this?
 
It would be really cool for you to do/get someone to do a heat loss calc. That way you know exactly what you ned to do, without overdoing...see disclaimer below:
 
And BTW...if you can get your mitts on a Wirsbo/Uponor radiant design manual..it rocks!...Try Ferguson Enterprises/Noland, see if you can mooch one from the heating sales dude.
 
please excuse the slight hijacking of your radiant thread, but if I get an answer here it may help you as well...

I've always been told that the max surface temp for wood floors is 85 degrees. But is that only for glued/parq/laminate wood flooring? Our old house has 1" thick hardwood floor (1" thick pine in some rooms)...is 85 the max surface temp for hardwood as well?

I believe that the temp max has to do with avoiding splitting or cracking or "drying out" the wood, but it's also my understanding that heat doesn't dry out wood, it only changes the relative humidity and that moisture is not lost unless it's condensed, etc.

thanks.
 
correct about 85 degree max for any wood floor, or correct about temp doesn't matter with non-engineered wood?

:)
 
I don't think you can go much above that...but I'm not a radiant pro, my ed is in old-skool stuff, like BB, radiators, steam.

BTW, FYI; Drawings/schematics for hot water heat piping schemes are justa couple clicks away...www.heatinghelp.com

Click on the resources tab...get edumacated!

:cheers:
 
Hi All, Thanks for this great information.
I'm in the process of desiging a radiant floor system for our home and also want to make up my own heat transfer panels out of flashing. I have a few questions and your help is most appreciated.

Did you staple the tubing to the floor then put the heat transfer plate over both? I plan on using the transfet plate to hold the tube into place since it will have a tight form to the plate.

What about noise? Have you experianced any noise while the components heat up and cool down?

Is it possible to get more info on how the groves were made? I dont have access to a log splitter and I was wondering if you had any other ideas on makine the groves other than by hand using a jig and pressing the pipe into the aluminum to make the form.

My problem is I will have to use a lump hammer to do the pressing.

Your help is most appreciated.
Thanks
Joe
 
Don't want to use ready-made staple-up components Joe?...Me thinks that with homemade plate, how do you determine heat transfer rates, and if it is enough or not? I know that stuff is pricey. I personally would invest in one of the staple-up guns available.
 
I did a staple-up radiant install for my first floor as well.

1. I used 1/2" PEX, one per joist bay. Some say two - if you have a very old or drafty house, you might need two. Then again, you'd be better off insulating throughly.

2. Use a water-to-water HX.

3. I'd stick with a max of 250'. I used 200'. You can go much smaller but then your water needs to be cooler and your manifold larger. Not really a problem. I probably wouldn't go below 100 feet in any loop.

4. Don't know max temp. Water temp should be between 125 and 140?

5. I used the plates, and also stapled up the foil-bubble-foil 'insulation' below that. It seems to work very well. I have a major allergic reaction to fiberglass insulation so it is not allowed anywhere in my house, and the only other option was rigid foam, which didn't seem necessary.

6. I used a standard programmable t-stat and circulator pump controller. My domestic hot water is on priority, followed by floor heating.
 
I have since revamped my set up since my last post. The way I had it before worked great and did a good job of keeping that room warm. The problem was, my furnace draft was running constantly and I believe I was using more wood.

I have since installed a water to water HX.

I stapled the flashing right over the 1/2 pex. I ran two per joist.

You could make some kind of jig out of blocks of wood.



Fasten a piece of 1/2 pipe to one block of wood (centered)

Then nail down two boards with a 5/8 gap between them.

Sanwich the aluminum flashing between them and wack with a heavy hammer.

I didn't try this but was considering it before the guy with the jig offered to make them. This block of wood idea would take a really long time to make all those transfer plates.


Here is a site that might help you. I used the parallel set up with two homemade 20' long manifolds made out of 1" copper pipe.


http://www.radiantcompany.com/details/joists.shtml
 
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1 yes, no HX unless your boiler overflow is lower than the highest point of your radiant, you'll need either a HX, or some back flow prevention valves

Fletcher, this is the first time i've heard this, and it makes perfect sense! Did you have to address this with your install? How did you solve it - with check valves or HX? If useing check valves are simple swing-gate valves ok? do you need one on the supply and return sides of the zone or only one side? Tell me or about this - thanks!
 
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