Pex tube and the sun

[Raspy]

Use the 1/2" tubing (ID measurement) and lay it out on 9"to 12" on center. Keep the loop lengths to 300' max and close to each other in length. More loops of a shorter length is better. Lay out the loops to heat the various areas, in other words, bedroom loop, kitchen loop, bathroom loop, etc. Route the supply and return ends of the bedroom loops down the hall or through some common area, if needed. Don't worry about closer spacing in the hall or around the front door, they can be right next to each other, if needed, as they proceed to the bedroom or other area. You can run the whole thing on one thermostat or as many as you have loops.

It usually takes about 1 1/2' of tubing per square foot of floor with 12" spacing. More for 9" spacing. Get plenty of tube. I don't recommend splicing it in the slab, if you can help it, but I do if it gets kinked or cut.

Put a double pass or closer spacing near the exterior door and. Put the tubes at closer spacing in the bathroom, probably at 6" if the rest is at 12" or just make it a double pass with the tubes next to each other.

DON'T kink it and make it sweep a return bend no closer that about 9".

Tie the tubing with rebar ties directly to the structural rebar in the slab. Slip the tubing through 3/4" PVC conduit 90s where it exits/enters the slab.

Set up a manifold with balancing valves on each loop. Set the manifold where the tubing can run conveniently to the heated area and where you can feed it from your boiler or hot water heater. The top of the manifold should be about 30" from the finished floor.

Be careful not to send scalding hot water to the tubing. 120 degrees is plenty and 90 will actually work gradually. So don't send the tubing water directly to the solar panels.

Have fun and "experience" the heat as you lay it out. More in the baths, less in the closet, more at the door, little or none in the pantry. Under the shower only if you can put in in the structural slab first. Closets are optional. Stay away 10" from the center of the toilet pipe. Lay the tube to pass through doors instead of under walls and plan ahead on where you might be drilling in door stops, closet door guides. Mark the plans carefully anywhere the tube passes under wall. Go through all doors in the same way so you can drill in thresholds later and know where the tube is.

Take LOTS of pictures or a video. Show reference points to measure from in the pictures.

Here is a picture of my place using 3/4" tube

 

[ultrarunner]

Use the 1/2" tubing (ID measurement) and lay it out on 9"to 12" on center. Keep the loop lengths to 300' max and close to each other in length. More loops of a shorter length is better. Lay out the loops to heat the various areas, in other words, bedroom loop, kitchen loop, bathroom loop, etc. Route the supply and return ends of the bedroom loops down the hall or through some common area, if needed. Don't worry about closer spacing in the hall or around the front door, they can be right next to each other, if needed, as they proceed to the bedroom or other area. You can run the whole thing on one thermostat or as many as you have loops.

It usually takes about 1 1/2' of tubing per square foot of floor with 12" spacing. More for 9" spacing. Get plenty of tube. I don't recommend splicing it in the slab, if you can help it, but I do if it gets kinked or cut.

Put a double pass or closer spacing near the exterior door and. Put the tubes at closer spacing in the bathroom, probably at 6" if the rest is at 12" or just make it a double pass with the tubes next to each other.

DON'T kink it and make it sweep a return bend no closer that about 9".

Tie the tubing with rebar ties directly to the structural rebar in the slab. Slip the tubing through 3/4" PVC conduit 90s where it exits/enters the slab.

Set up a manifold with balancing valves on each loop. Set the manifold where the tubing can run conveniently to the heated area and where you can feed it from your boiler or hot water heater. The top of the manifold should be about 30" from the finished floor.

Be careful not to send scalding hot water to the tubing. 120 degrees is plenty and 90 will actually work gradually. So don't send the tubing water directly to the solar panels.

Have fun and "experience" the heat as you lay it out. More in the baths, less in the closet, more at the door, little or none in the pantry. Under the shower only if you can put in in the structural slab first. Closets are optional. Stay away 10" from the center of the toilet pipe. Lay the tube to pass through doors instead of under walls and plan ahead on where you might be drilling in door stops, closet door guides. Mark the plans carefully anywhere the tube passes under wall. Go through all doors in the same way so you can drill in thresholds later and know where the tube is.

Take LOTS of pictures or a video. Show reference points to measure from in the pictures.

Here is a picture of my place using 3/4" tube

Looks like a great project! I like the structural steel.

Did you have it fabricated local or outscourced?

 

[Raspy]

I bought a steel 48 X 60 building with a 12' extension on one side. I eliminated the diagonal seismic bracing and went with rigid box bracing that keeps the design open for windows and doors. Then I added their 3' overhang/eve kit, in steel, on the other side. I deleted the steel siding so I could use Hardy plank siding.

We set 3' square footings under every post. These go down 3' below grade. Then we poured connecting stem walls in between them. The front porch was poured hollow to make a room below for storage. A 12 X 60 back porch slab went in (under the overhang), the front porch was poured, then an 8" slab with radiant heating throughout. Then framed the whole house, sheeted the entire place with 5/8" OSB and sided it with Hardy.

I added a separate 12 X 14 steel frame and roof structure to become the front porch and set it at 90 degrees to the main building.

The roof was on for a year before we poured the slab and started framing.

Now I'm wiring, it's all closed in with windows and a wood stove.

We won't finish for another year or so.

What a project!

 

[ultrarunner]

Sounds like the ultimate in construction and well thought out.

Like to see any other pictures and how your take on the radiant set-up

What fuel will you use to heat it?

 

[Raspy]

I can't show you anything on the heating system because I haven't installed the solar collectors, the storage system or the boiler. It will have (6) 4 X 8 collectors and 360 gallons of storage. The collectors will be arranged as a "drain back" system and will gravity drain to a small tank for freeze protection. A heat exchanger transfers the heat from the storage to the radiant loop. The setup uses a "solar" thermostat in the house for the "desired" or "max" temp. Then the other thermostats set the "minimum" allowable temp and run the boiler. A simple switchover system enables or disables the boiler burner depending on the available stored solar temp. So, the house has to be below the minimum temp and have no solar available before the boiler can start. The boiler vent pipe has an air to air heat exchange to supplement the garage heat. Fans in the living room and garage send down the stratified heat near the ceiling. Solar will be the primary heat source for the radiant and hot water. The backup will be heating oil on the radiant and an electric water heater for the hot water. There will be four thermostatic zones and a very simple control system.

With four thermostats we can just heat the areas we are using, and to different temps. The floor itself will act as some storage and wood heat will give the house a shot of heat in the mornings and evenings. The garage is about 1000 square feet and has it's own thermostat.

With radiant, the house doesn't have to be warm to feel warm. The nice floor temp can be cooler in the bedrooms for sleeping, warmer in the bathrooms and kitchen, and somewhere in between in the living room. It can be left off in the garage until I'm on a project and left off in the unused 2nd bedroom.

If I'm getting too much temp in the storage tanks I can add more to the floor for storage and if I'm beginning to use more oil than I want to I can lower the floor temp a bit or shut off unused rooms. Or the whole thing can be left alone and run automatically. I have (2) 300 gallon oil tanks to feed the boiler.

By next winter I hope to have the system running. Can't wait!

 

[mx842]

Hi Folks
I am thinking about installing pex in the concrete floor of a 30x50 foot garage, I used pex in a house we built 3 years ago and really like how easy it was to work with. we used the Uponor Wirsbo brand tubing. I need to find the best way to lay out the tubing and feeding it without using up a lot of wall or floor space. our plan is to use solar heated water and or an outside wood furnace to heat the water. If someone would have pictures we sure would like to see them. should we use 5/16 or 1/2 inch tubing? How many zones should I use or can I just use 1 large zone area? also how much tubing do I need to use? the tubing is about 600 dollars per 1000 foot free shipping from pexsupply.

Charlie

Well Charlie you asked a lot of questions and you will get many answers but I'll try and give you my opinions. I did so much research before I started this project and asked so many questions on boards like this that I couldn't keep up with all the sorted answers. I decided one day to just take the information I had gathered and go for it. There are so many people selling this stuff and they all have their own selling tactics and it is really hard to decide to even buy your equipment from. I finally narrowed it down to three companies and I eliminated these by flipping a coin and making an order. I ended up going through 4 companies before I found one that had everything I needed and I still had to settle for connecting two manifolds together to get the number of loops I needed because the right manifold was out of stock.

You don't use up any wall or floor space because the pex is buried in concrete and you can put the equipment in a small closet so that it is protected and out of the way. You are looking at 1500 sq feet so you will need at least 6 loops.

Every setup is different and I don't know how and what you will be using this space, if it will be all open or cut up in different rooms or sections where one place you want heat and someplace you don't. If it is all open and you want to evenly heat the whole thing I wouldn't go with anything less than 1/2 tube. I wish now I had gone with 5/8 because the price was not that much difference and you are putting more heat per sq inch for almost the same price this is because you don't need as much of it.

If you are going to have walls and partitions throughout make sure you lay out the pex in a way it is not directly under a wall or someplace where you have to place anchor bolts. You can route the tube in and out of partitioned areas by running the tube under doorways. Try not to get in the position where you have to lay one tube over another to get from one place to another. You need to lay this all out on paper as to how the loops will run so that when you actually get to the point to where you are running the tube you know how and where it needs to be run. Pex is hard enough to mess with as you are rolling it out so you don't want to get 200' rolled out and tied down and then find out it is put down wrong and have to take it back up to reroute it. That is one genie you don't want to have to try and stuff back in the bottle.

If there are partitions you also may need to have different zones dependent on your needs. But if it is all open 1 zone would be best and try to put the service closet somewhere on one of the 50' walls about mid way if possible because the runs will be easier to lay out that way. You need to keep all the loops as close to the same length as possible. Don't worry about a 10 or 15' difference in one or another but do try to keep them all about the same. You can adjust one way or another once you start to lay out the tube and you will probably find out that the actual tube you lay out will be a little shorter than it was on paper.

If you use 1/2 you need to keep your loops to under or right at 250'. If you use 5/8 you can go up to 300' per loop. You have to decide if you are going to use insulation under the pad or not but if you are in a cold climate you will want to do what ever you can to keep the heat in the concrete and not over in the neighbors yard. Cold climate? The colder, the more insulation you need to put under and along the sides of your slab. If what you are doing is going to be inspected by some gubment agency, don't worry they will tell you what they want. There is no real answer to what you need as I have heard of people putting down from 16" to none it all depends on how cold it gets where you are. Some people insulate just around the sides and then 4' to 8' along the inside floor area and leave the center open and use the ground itself as a heat sink, it all depends on the climate and your own personal needs.

Once your vapor barrier (at least 6 mil polly) is laid down and the insulation you are going to use is laid out and taped in place you lay out your rebar or other reinforcing material on top of the insulation. I like rebar rather than the roll wire type because it is easier to work with but it does cost more. I laid mine out starting on the outside edges at 1' then I went to 2' from there and what you end up with is a bunch of two foot squares all over the floor that you can use as guides to run your tube. I tried to make my hot tube be the one on the outside wall and that one can vary from 6" to 1' depending on what's in the way and then make my loops keeping in mind the length I am so I can end up to where I can loop back over to the hot loop on the wall and back to the manifold while trying to keep the total length around the 250' mark.

The next loop will start 1' over from the last return tube if you are using 1/2" and on from there until all the loops are down. How you run them makes no difference as long as you try and keep the lines spaced close to the same distance and all of the floor has relatively the same coverage. Loops will wonder a bit but where you give up a little here you will pick up somewhere else as long as you end up with 6 loops at around 250' each without having to cross over a loop you should be good. Also I might add that anywhere the pex enters or leaves the concrete it needs to be supported with some sort of protection. The grey electrical conduit works great for this because they have 45 and 90 degree bends you can buy that are perfect for the pex to run in and out of the manifold box.

There are tons of people here that know far more about this than I do about this subject but these are just some of the basic stuff that is fresh in my mind from doing my layout. I'm sure they will chime in if I have written something misleading.

 

[Raspy]

Charlie,

Just to clarify tube sizes I want to remind you that 1/2" tube is 5/8' OD. 3/8" tube is 1/2" OD. Tube is measured on the inside diameter. When you order, if you say 1/2" tubing, you'll end up with 1/2" ID, 5/8" OD.

Don't use 3/8" tubing in your slab because it must be shorter lengths and it's more fragile. Actually, 3/4" tubing, (7/8" OD) is best of all for big open slabs. The stuff is nearly indestructable and has a lot of surface area, but it is a lot stiffer and harder to work with.

I also strongly recommend against placing the tubing on 2' centers. The recovery rate will be very poor and the warmth will be a patchwork all over the floor, instead of a nice even temp. 2' will deliver enough energy to heat the place, but will have lower practicality and lower comfort. Stay with 1' on center max, and less in special areas as I've described. Use plenty of tubing!

Remember 300' max for 1/2" tube as a general rule of thumb, but 9 loops of 200' each is often better than 6 loops of 300'. Lower restriction, more even heat and better balancing. It's OK to get a manifold with more drops than needed. You can just make a short jumper loop across the manifold to use up the extra set of drops and it gives you a place to short circuit the floor loops for startup. Sometimes handy.

Also, if you are going to have multiple thermostats, you can run them all off one manifold by installing telestats on each loop. Be sure to get a manifold that has available telestats or, often called, power heads, if you are planning more than one stat.

 

[mx842]

Thanks Raspy for bringing up not going 2' distance on the tubing. I was thinking about doing an edit to my last post to clarify. When I wrote that post I thought I was clear that the rebar was laid down in two foot squares but the tube was laid out 1' apart if 1/2" is used. The first and third tube runs along a rebar and you have one in the middle that you can tie down every 2'. Half inch is plenty stiff to where it stays down when tied every 2'.

Also I wasn't clear when I wrote about the 250' vs 300' per loop. You of-course are right about the loops of 1/2" being able to go the full 300'. The 250' thing for me made sense because the way I figured I could buy a 1000' coil and get 4 loops out of it and not have any left over. The way my floor was laid out I couldn't make it work out using 300' loops.

Oh yeah, the clarification on tubing size was a nice added touch, I was just assuming everyone would be thinking ID when speaking of 1/2" and 5/8" tube size. I always get into trouble with my assuming thing when writing.:laughing:

 

[jimgerken]

Lots of great advice given so far. I would add a couple points. In my opinion there are two reasons for under-slab insulation. FIRST is obvious as discussed: to heat the slab you must insulate it from the cold ground. The ground seeks to equalize at some local temp, say 55 F in my area, below the frost line. To attempt to pour heat into the ground to raise it to 80 degrees is pointless, it will never get satisfied. SECOND reason is to allow the concrete to stabilize at or near the room temp, in the Springtime, about a month sooner than it would without insulation. Without insulation the slab contacting the ground stays much colder for a month than the air temp is, so condensation can be a crazy mess. Insulate and break that contact with the cold ground.

A great source of insulation is re-use. These guys broker the used insulation in warehouses all over the USA, and are good to deal with:
Welcome to Insulation Depot - Rigid Foam Insulation, Used Insulation, Roofing Supplies, Roofing Material

Consider the useage of the building carefully, as was suggested. Zone appropriately. In the last one I laid out I used the 12 inch on center spacing for the tubing but then purposely left a few feet around the outside of a large area of the building where I knew storage would be taking place (like all along one wall where I knew there would be stuff setting, or cabinets and benches located) without tubing at all. In other words, I left several feet in, along the perimeter of two sides of the slab, without any tubing. Research showed me that concrete has an "R" value which makes 33 inches of concrete equal to almost R-5. These outlying areas do not have to be comfortable on the floor temp, its a shop not a livingroom. There will be "stuff" setting there anyway. Like benches and cabinets. So I am not trying to heat that area, and the distance the heat has to travel thru the concrete (about 36 inches) acts to slow the tendency of flow, just as insulation would. Of course I do have perimeter insulation too, four inches thick XPS.

There is a cool new product you can use. Its called EZRoute. Works great.
EZRoute - Products - Premier

 

[Raspy]

I used 2" blue board as my slab edge insulation and kept the tubing back 1' to 3' from the inside of the walls, all around the perimeter. No insulation under the slab.

The reasons I did not insulate under the slab were that I did not want the slab to be supported by crushable insulation and because insulation merely slows heat transfer, not stops it. So, with insulation, you might get a faster response if you put a lot of energy into the slab, but if you keep it warm there shouldn't be much difference.

People keep saying the heat will be lost or you'll be heating the Earth, etc. But with a dry gravel base with no air movement, you'll just have some additional mass. There really is no mechanism to move the heat a long distance, just conduction.

With the heat held back from the edges and with slab edge insulation that goes down below ground level and reasonable floor temps of 75-80 degrees or so, I can't really see the value in underslab insulation. If you factor in the cost and reduced stability, it looks like a bad choice to me. However, if you do want it, and it's personal decision, void forming might be a good choice instead of insulation. The worst is probably the blister pack, bubble wrap insulation with low insulation and a weak structure.

Another factor is the climate. The Bay Area in California is very mild and we use little insulation under the slabs, but if it was extremely cold I think it would make more sense. Or just add a lot more to the edges and be sure to hold the heat back around the perimeter.

Good insulation in the walls and ceilings, and good windows are very important.

Oh, by the way, do any of you need a few ladybugs? :laughing: Just took this picture this morning. Check out our sleeping coyote.