cut off valves

I am installing underfloor heating in a few rooms. Coming from the oil burner I have a two 3/4" copper pipes running, one supply and one return. Coming off of these pipes I will have three separate runs to PEX tubing, one for each room. I want to be able to control how much water (and thus heat) is flowing to each of the three rooms, so I want to put a shut off valve before each leg of PEX. There is a thermistor in the floor of only one of these three rooms. I was planning on just putting a cutoff valve on the supply side leading to each PEX run. But now I am thinking, what if I have a problem with one of those three runs (like a leak)? Am I beter off putting in valves on both the supply and return of each run, or will just one valve per run do it? I am not looking to over engineer this thing.

One more thing I forgot to mention. I am only attaching one of the three PEX runs at this time. So when I put in tees to a missing PEX run, I will need to cap it off for right now. What do I use to do this?

Re: heating sys remodel

First off, I don't think PEX heat tubing is rated for full boiler temp. water. In order to run PEX you have to temper the water, by using a 4-way adjustable valve that takes in cool return water to temper the hot outgoing water to a temp the PEX can use w/o expanding to splitting.

Be carefull,

Rudy

Yes. You are quite correct. I didn't bother mentioning it but there is alot more stuff between the boiler and the PEX such as mixing valves and pumps. My question concerns cutoff valves.

You could put a zone valve on each branch and control it with a thermostat. You'd need a controller that would react to each room's needs and turn on the circulator and the boiler. An alternative would be to control each zone with its own circulator controlled by the room's thermostat.

Note, when using only one circulator, the volume will vary depending on which loop is open, you may need an overpressure bypass valve in the system to compensate.

I have only one thermistor which attaches to one pump. It is built into the floor of one of the rooms. The thermostat is back in the boiler room (it is not user controlled). But I do want to be able to balance the heat in each room via the valves. Question concerns whether to have a valve on just to supply side to each PEX run, or on both the supply side and the return side of each run. I guess I am paranoid that if one of the PEX-runs springs a leak sometime in the future, I will need to turn the whole thing off, instead of just one room's PEX tubing.