1 1/4" Pex-al-pex for 250' run?

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Isaac

Member
Apr 5, 2010
8
Idaho
After lurking a couple years, and piddling at building my own house, I've got questions - too many to ask at once, but I'll try to start simple.

I've got an open trench right now (for power and domestic water reasons) between what will be a future shop, and the greenhouse where the boiler and 2000 gallon storage tank live. While the trench is open, I want to put in my PEX lines, insulate them, etc., though in all likelihood, it will be 5-6+ years before I get to building the shop (house still needs to be built). The trench is about 235' one-way, the shop will be a max of 3000 ft2, (30x50' two floors). It'll be well insulated, think of it like a simple house with a garage below. Lots of unknowns, a few years ago I found a BTU calculating link somewhere here, I can't seem to find it now.

I see a couple possible scenarios:

1. Sprayfoam 2 lines of glued 4" PVC solid drain line into the trench, and pull the appropriate size PEX through at a later date. Seems like not as good of idea as just laying the lines now...but as plans always change...

2. Sprayfoam 2 lines of Pex in right now, build and underground box up near the shop, and cover/bury them until we start on the shop.

Question about the sprayfoam, talking to the local sprayfoam fellow, there are different weights of close-cell sprayfoam, the more weighted foam, the higher the water resistance. What weight closed cell foam are folks here using for spray in trench?

O2 barrier Pex or not? Yes, I've read here how important O2 barrier is, but in my case of an open system with a 2000 gallon tank...the line going to the shop is going to have to be its own closed system with a heat exchanger because the shop is up hill from the greenhouse (thus the tank would overflow with the open system). With this as the case, would you still spend the extra for O2 barrier Pex?

Pex size...I know, I need to do more homework on this. I did some calculations a year ago and came up with 1.5" pex to keep my power/pump consumption down. But I'm wondering if I could get away with 1.25" lines. I want to do this right, and not squander power. I've been off the grid for 10 years w/o power, and just because I'm getting it now, I don't want to start squandering it. Any advice?

Lastly, anyone have experience with this seller on ebay?

http://stores.ebay.com:80/New-Journ...id=20689309&_trksid=p4634.c0.m14.l1513&_pgn=2

He seems to have 1.25" Pex-al-pex for a reasonable price. I'd be interested in the 1.5" non O2 barrier pex he has for the same price, but when I talked to him, he says the ID of the 1.5" Non O2 barrier Pex is about 1.25; and that the 1.25" Pex-al-pex is a true 1.25" ID.

Thanks for the rookie help - much appreciated. (PS - if slow to respond its because I'm still off-grid...)
 
You have a lot on your table! A major consideration is determining how many btu's you need to meet your needs, in other words, a heat loss calculation. That, along with calculations, will let you know whether your 1-1/4" line will meet those needs. A rough calculation on 1-1/4" x 470' at 14 gpm (typical 140,000 btuh) results in about 25' of pump head, plus of course additional head on one or both sides of the run of tubing. That's getting quite high, reaching the upper range of normal household circulators, and getting into the range of commercial circulators. Two 1" lines, each moving 7 gpm, have about 20' of pump head. You're going to need to carefully think through your project. Perhaps the cart is in front of the horse to plan now for your underground piping. You don't want to make an expensive mistake.
 
Isaac, Jim gave you good advice.

I ran a quick heat loss on a 3000sq/ft, 2-story, lots of windows, 9’ ceilings at http://www.alternateheatingsystems.com/BTUCalculator.aspx , It came up with 82,500 BTU@ -30 design temp but it did not ask for heating degree days (http://www.ncdc.noaa.gov/oa/climate/online/ccd/nrmhdd.txt ). These are others: http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm , and SlantFin, the one I used for my initial calculations. http://www.pvsullivan.com/Downloads/SlantFin/he2setup.exe . It is a large 173Mb file so it takes a while to download. This was a popular application when I started looking.

With SlantFin, (Our heating degree days are greater than Pocatello, ID) my house 4,500 sq./ft, 2 levels is 94,000. I have good insulation (sprayed cellulose, walls and ceilings) and good (lots) triple pane windows. 63’- 14.5’ cathedral ceilings, rest of house 9’ ceilings.

I feed 200’ (400' loop)to the HX in the house with 2-1†HePex lines. I have a Grundfos 15-58 on each line. I only run one pump till the temperature starts dropping below zero. I have reached a Delta T 25-30 degrees with one pump @ 4.5gpm. Sizing the HX was good advice from this forum. I may add, with the help of the forum once again, I can not measure a degree of heat loss over the 200’ underground line to the HX.

If you know the dimensions of your house and the quality of the insulation, windows, doors, etc, you should be able to come up with some reasonable BTU needs.

Spend some time with these calculators and your designs to get an idea of your heating needs, then you can choose your pipe based on required flow, and calculate your head and choose your pump. As Jim said, if you design the piping wrong, the mistake could be expensive.
 
Thanks for the replies. Yes Jim, the cart is out ahead of the horse, and as much as I hate that, I hate worse bringing in a backhoe to tear up the land and the trees like I did, so I'm really struggling not to put in some means for lines at this time. I really don't want to tear things up out here again down the road.

I've read here where a couple folks have 4" pvc lines in insulation, and have pulled Pex tubing through them. That would be an option. If you plug the ends up real well, can anyone comment on the effectiveness of this method?

George, thanks for the links, I'll sit down and do some homework on it tonight.

Again, thanks.
 
Go ahead an place two 4" pvc pipes and insulate them with spray foam. just cap both ends and leave buried. Be sure to place a re rod horizontal marking the location. It can be picked up with a metal detector if lost. Then when you decide on tubing just pull it thru. Prolly a good idea to add in a spare chase for other uses.

Will
 
Maybe feed a polypropylene cable pulling rope (rope, not string) through each conduit as you assemble it so you can pull (as well as push) the pipe through when you get to it.

250ft. of stiff PEX is not going to cooperate.

Wouldn't 3" pipe be adequate?
 
if you decide to use a pull rope, all ya need is a mouse the size of the pipe and a shop vac, it will pull in a string to pull in a rope in 20 seconds. FYI - use conduit sweeps for any turns - it will glue with schedule 40 pipe or just use conduit - done both.
 
If you are unable to determine what the actual heat loss of the garage/house is going to be, I would bury the 4" pipe, insulate it and slide the tube in later. Buying larger tube than you need isn't nearly as bad a buying too small but why waste the $$.00 ?

Using the pex only and not figuring any fittings, valves or other restrictions, I show the following flow rates.

Circulator is a Grundfos 15-58 on speed 3. 1" pex = 4.75gpm, 1-1/4" pex = 7.33gpm and 1-1/2" pex = 9.88gpm

As you can see the percentage gain in flow is far greater from 1" to 1-1/4" than 1-1/4 to 1-1/2.

The other thing that enters into the tube size equation is how much your heating system can drop the temp from supply to return. Being able to grab 30 or even 40* out of the flow will drastically reduce pump and tube size compared to a delta T of 10-15*. In Europe it is very common to see systems operating with 30* or higher temp drops which can sometimes really reduce the size/mp draw of the circ as well as the tubing required to carry the flow.

We did a system last winter that flows about 3gpm and heats an old farmhouse very nicely. The key was having enough of the right kind of emitter to drag the heat required out of that low flow. It drops about 34-42* depending on what's running in the house.
 
My calculations are not quite the same as Heaterman, but it doesn't make much difference because we have too little data to make a more accurate calculation. The point Heaterman makes "The other thing that enters into the tube size equation is how much your heating system can drop the temp from supply to return" is well taken. At 7 gpm and 20F supply/return temperature drop, your heat transfer will be 70,000 btuh, but at 40F supply/return temperature drop, your heat transfer will be 140,000 btuh. Designing for low temperature emitters will pay big dividends in lower heating fuel cost, and less cost in up-front hardware to deliver the hot water, that likely far outweighs the extra cost of low temperature emitters. Think efficiency in everything design as you move forward.
 
EGG ZAK LEE!!

It has to be looked at as a system, not just a collection of pieces and parts. Design with a goal in mind. Think how the btu's get on the train. travel to the destination and then get off the train.
 
Thanks all, still reading, processing, and researching here. Most everything your saying makes good sense. Radiant in concrete floor is considered as efficient of a low temp emitter as possible correct? Still working on how to radiant the upstairs, would rather not have concrete up there. Again, thanks for the feedback and the BTU calc. links.
 
Isaac said:
Thanks all, still reading, processing, and researching here. Most everything your saying makes good sense. Radiant in concrete floor is considered as efficient of a low temp emitter as possible correct? Still working on how to radiant the upstairs, would rather not have concrete up there. Again, thanks for the feedback and the BTU calc. links.

Use panel radiators with a variable speed pump and move the water at a very low rate. Mine do very nicely with about 1/19th of a gallon per minute per radiator. If your house design is basement/main floor/ second floor, I would consider tubing the basement slab and using panel rads on the upper two floors if it were me.
 
The heat loss of the pipe is partly based on it's diameter (larger pipe has more surface area) - running PEX through 4" pipe (even if the 4" pipe is well insulated) would have much more heat loss than directly burying 1 1/4" PEX (or whatever size is appropriate for your design) and directly insulating the PEX with the spray foam. Use spacers to keep the return and supply lines from touching each other in the trench before you spray foam.

For example, a 1" pipe with 1" of spray foam on it would have much less heat loss than a 2" pipe with 1" of spray foam on it. You could calculate the difference:

http://www.engineersedge.com/heat_transfer/conduction_cylidrical_coor.htm
 
Isaac said:
Thanks all, still reading, processing, and researching here. Most everything your saying makes good sense. Radiant in concrete floor is considered as efficient of a low temp emitter as possible correct? Still working on how to radiant the upstairs, would rather not have concrete up there. Again, thanks for the feedback and the BTU calc. links.

Concrete upstairs is absolutely no problem. After the platform is down for the upstairs deck, place a two-by in every location you are planning a stud wall. Attach the radiant tubing to the plywood deck. Pressurize the tubing, test for leaks, and connect it to the city water supply or a pressurized well system. Place 1.5" of pea gravel concrete that is a little over sanded. The transit mix supplier will have a standard mix for this and can give you a quote. Get a steel trowel finish on the concrete. There will be shrinkage cracks. Easily repair these with liquid floor repair material commonly used by flooring guys.

Erect stud walls over the locations of your two-by forms. We have been in ours about 20 years with no problems to date. Ours was constructed by local guys with the normally good knowledge they possess. Special installers are not required.
 
Just a caution on the concrete over pour, over wooden subfloor. Don't try it unless you KNOW that your basement footings, basement walls, main floor walls, floor joist or engineered truss floor can carry the proposed load. You will be adding several tons of weight (times two storeys) to your structure & you need to know that it WILL carry the load, as well as not having severe deflection in floor joist/trusses from the extra load.

In the absense of any load tables for your structure, I would be far more inclined to follow the suggestion on panel rads for upper floors. If your wife likes warm floors (as mine does) then consider some of the aluminum plate backed underlays that are pre routed to receive hydronic tubing, installing these is fairly easy & simple. They will ad very little weight to the structure. Attach them to your subfloor, install tubing, cover with flooring of your choice. I prefer laminates & tile for durability/service life. Either way plenty of low weight/high eff options out there for you to consider.
 
Frozen Canuck said:
Just a caution on the concrete over pour, over wooden subfloor. Don't try it unless you KNOW that your basement footings, basement walls, main floor walls, floor joist or engineered truss floor can carry the proposed load. You will be adding several tons of weight (times two storeys) to your structure & you need to know that it WILL carry the load, as well as not having severe deflection in floor joist/trusses from the extra load.
...

Definitely agree with this.
 
JimboM said:
Frozen Canuck said:
Just a caution on the concrete over pour, over wooden subfloor. Don't try it unless you KNOW that your basement footings, basement walls, main floor walls, floor joist or engineered truss floor can carry the proposed load. You will be adding several tons of weight (times two storeys) to your structure & you need to know that it WILL carry the load, as well as not having severe deflection in floor joist/trusses from the extra load.
...

We put down the aluminum covered pre-routed plywood as subfloor in our new kithcen and family room. Pex-Al-Pex went into the groooves and the whole thing was covered by hardwood flooring. These are the most comfortable rooms in the house in the winter. The heating is gentle and silent and both the kids and the pets no longer have to fight to see who gets to lie on the kitchen floor in front of the single hot-air register. We were in a good situtation in that we had to remove the old floor and subfloor anyway, so this heating system was an ideal fit. It would work just as well in new construction.
 
Reviving an old thread. For those interested here are some photos of how we sprayfoamed the lines. Maybe it will help others, maybe it was a good way, maybe not, but it is done and buried. It will be years at my current building rate before they are in use, but thats another story...

We attached the lines to the foamboard with zipties, using the foamboard to separate the lines, then sprayed, and gently placed the sprayed line into the trench when it was partially cured. Hope it's helpful...and I sure hope they work when the time comes!
 

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