primary & secondary loop piping

Unknown

Check the installation guide that came with the boiler. Most show how the manufacture intended it to be installed. Or just call the manufacture and ask the tec. support. This way if there were any issues in the future you did it their way.

Pat McEnroe

primary & secondary loop piping

Last year I installed my wall hung tankless boiler - I was in a bit of a hurry and only needed to connect 1 loop for a coil in the air handler and another for a radiant loop in a bathroom floor.

Now I'm ready to connect some more loops and I'm wondering what is the best approach. The final system will have:

Air handler (120,000 BTU coil)
2nd floor radiant loops (all with ceramic/stone tile, individual thermostats)
2nd floor cast iron radiators (each run from a manifold but a single thermostat)
first floor cast iron radiators (each run from a manifold but a single thermostat)
future first floor radiant loops (under hardwood)
future addition (second floor) radiant loop (under hardwood)

In addition, I will be adding an indirect domestic hot water storage tank.

My question is this - should I have a single set of closely spaced T's on the primary loop and then run manifolds for supply and return for each of the secondaries (with mixing valve(s) for the radiant loops) or should I just place each secondary loop off the primary loop?

Either way, is there a 'best' order of arrangement on the secondary loops or does it not matter?

Thanks and Merry Christmas!

Pat

Brad White_184

Different temperatures/flavors

Personally, I would run specific, individual temperatures to each type of emitter. (The DHW-generating side of things I will assume has priority to limit and is in parallel, separate from the heating side.)

Not knowing how you selected each emitter, I can only assume that on the heating side, the air handler will take the hottest water and will govern the boiler's high limit operating setpoint.

Next would be most likely the under-wood radiant floor followed by the CI radiators (manifold) and then the ceramic tile radiant areas. These last two could well be switched for all I know. Your ratio of CI radiators to heat loss may be high or low. If high, a lower water temperature than even the wood floor may be possible.

In answer to your question, you should use separate circuits for each temperature with a mixing device in each.

You could make all of these temperatures in parallel with each mixing device seeing the same higher temperature hot water (as set by the air handler's needs). In the alternate you could run the tees in series as a "cascade" whereby the AHU goes first, dilutes the main but to a point still plenty warm to serve the next tier, then continue down to subsequent temperatures. If you are confident in your temperature requirements, this can be a simple way to go. For most flexibility though, I would give each mixing device the same starting temperature and mix down from there.

Rather than me guessing, you should figure out the specific water temperature requirements of each emitter set. You may well find that the CI and wood floors can operate within five degrees of each other, in which case one temperature can do nicely and be shared between them. You could save a mixing device and control point.

Pat McEnroe

Brad:

Thanks for the suggestions. I'm using existing two-pipe steam radiators. In some cases the radiators are over-sized (due to addition of insulation and sealing windows) but not all. This is the reason I thought using manifolds for these was a better way to go - I can adjust the flow at each radiator independently, or even add thermostatic valves on the radiators down the road. The boiler has outdoor reset control - I plan on using a relay to defeat the temperature input when the air handler is active so the boiler will go to max (180 deg) temp.