With your 1/10 the pump power calculation does it allow the use of a smaller pump then the 135w one ?

Since your looking for possible reasons why you shouldn't do it.

If you are worried about the T fittings failing enough that you would consider exposing them for a projected repair maybe you shouldn't do it.
I think durability should be of the up-most concern, how much is the gain are you expecting, if you cut up and T fit the pipes ? If its not substantial then for reliability reasons i would go with a one piece line or as near to as possible.

The 135W pump is for my solar hot water panel water loop. The solar loop will put heat into a water tank in the basement (which isn't made yet). This loop I'm talking about in this thread would be a seperate loop that will pull heat out of that tank to heat the house.

I wouldn't say I'm worried about anything at this point. Tons of plumbers make PEX connections inside walls every day and don't worry about them leaking. Mains water supply runs at about double to triple the pressure versus a closed loop hydronic setup, so that also minimizes risk.

I'm confident at this point as long as its pressure tested before the flooring goes over it, that it should last many many years. I probably wouldn't be as confident if I were pouring concrete over it, but I am not using concrete. I could further reduce risk by again reducing the amount of TEEs in the system. I would like to run one some more calculations with just two or three parallel runs to see what the differences are.

Anyway, I still have a lot of calculations left to do. This shows the pressure head for a single 100 square foot room. My house is roughly 1600 square feet. I'll have to design the system both ways and see what the difference is, or find some way to estimate it accurately.

I've been researching the idea that purging the parallel system would be troublesome because you need enough flow velocity in each parallel branch to move air pockets. This appears to not really be that large of an issue. The typical flow velocity needed to move air is a recommended 2 ft per second. This is the velocity required for inclined piping with water flowing downard trying to push the air down. For horizontal lines that are in a floor, the required flow velocity is actually much less.

According to this paper, the flow velocity for 3/4" HDPE pipe (it is a paper on ground source heat pumps so that is as small of pipe as they tested), the required flow velocity for horizontal piping is only .9 feet per second. I've copied the chart from the paper below, and you can see as you reduce the pipe diameter, the required flow velocity is reduced. For 1/2" piping I'd imagine I only need around .6-.7 feet per second.

http://ecorenovator.org/forum/attach...1&d=1350482474

Another interesting aspect here is that 50-60 degrees is the actual worst angle for air purging according to the paper.

Anyway, to achieve .7 feet per second in 1/2" pex tubing, you need a flow rate of .4 gpm. Under normal conditions we're flowing .167 gpm. So, we need to boost the flow rate by about 2.5X to purge the air. This doesn't seem like it should be all that hard to do IMO. If you have multiple zones on a home run type system, you should be able to boost any one loop by 2.5X the flow rate.

I've still been thinking about this. Another downside to having multiple parallel loops in one room is a reduction in the easy of dealing with obstructions and/or oddly shaped rooms. Careful thought must be put into the parallel loop length if you have anything the tubing must be routed around.

I had a concern which you already answered....reduced flow rate in the parallel scheme. So, my next wonderment is....is the heat shed from the parallel loop the same as one continuous loop? IOW, is the return temp lower? I ask since I have no idea at the moment.

I believe it is. The flow rate is still the same, and the surface area of the pipe is the same. Flowing X amount of water over Y amount of surface area should net the same heat transfer.

Couldn't you just run five or six parallel loops in the floor, run them all to the garage or basement or wherever your manifold is, and join them all there before connecting them to the manifold? That would give you similar flow characteristics, and all your couplings would be easily accessible and fixable.

Also, as far as pump size is concerned, I don't know how small a pump you want to use, but I'm running this one:

0015-MSF2-IFC - Taco 0015-MSF2-IFC - 00R 3-Speed Cast Iron Circulator - Integral Flow Check, 1/20 HP

It's completely silent and runs at speed 1 (78W). I've got over 1000 ft of tubing with the longest loop being 250ft, and the pump has no problem achieving 1gpm flow, which is plenty for my purposes. The pump shouldn't need to run more than 15 minutes out of an hour, good insulation provided, which would put it roundabout 460Wh a day.

Yeah, that would work too. Its a bit more tubing to run, but safer from leak problems.

This might present a problem if you're using a zone control valve though. You'd have to tie them together before the valve somehow. Not a big deal really.

I haven't even come close to choosing a pump yet. However, I'm really thinking that I'd like to go with an ECM pump due to increased efficiency and variable speed. This will probably end up being a Grundfos Alpha or Wilo ECORFC.

I have another thread about ECM pumps here:
http://ecorenovator.org/forum/applia...cm-motors.html