Hot water coil and radiators same time

bombaloo

Hi
Am I able to combine radiant heat (hot water flat panel radiators) at a lower temperature like 140 with a hot water coil running to a high velocity system (spacepak) at a higher temp like 180. Is the same boiler able to output different temperatures to different systems?

Jamie Hall

No problem. It's done all the time. The boiler puts out the higher temperature, and you use a mixing valve (which combines cooler return water from the low temp circuit with just enough hot from the boiler) set to the correct output temperature on the lower temperature circuit. The low temp circuit needs its own pump and, depending on the boiler, it's best to operate the whole thing as primary/secondary, so the high temp circuit also gets a pump along with the boiler circuit.

HVACNUT

You say "combine" rather than "zone".

If you're looking to control both the hydro coil and the panel radiators from the same thermostat, do the rads and coil heat the same area? If so, follow what @Jamie Hall said, then add a 2 stage heat thermostat. Use the hydro coil as a Stage 2 auxiliary. 

bombaloo

What if it was two separate thermostats. The first stage heating for the spacepak would a heat pump and the second stage auxiliary would be the hydrocoil. The heat pump would be for shoulder seasons. The radiators would be on their own zoned system as the primary heat source during the winter months and I would only turn on the auxiliary hydrocoil heat to supplement the radiators if I really need additional heat in the coldest days. Does that even make sense or is it unheard of to have a hydrocoil for auxiliary heat when you already have radiators. 

pecmsg

The in floor should have an outdoor reset control.

Your space pack would require a 2 stage t-stat.

bburd

@bombaloo If correctly sized, either radiators or a hydro air coil should be able to provide all the necessary heat even on a design day. Is this an existing setup? If not I don't know why anyone would install two separate hot water heating systems  to serve the same area.

if you have existing radiators and they don't keep the place warm enough, it will almost certainly be easier and less costly to correctly diagnose and repair the problem (low supply water temperature? Insufficient flow? Poor balancing?), reduce the heat loss or add more radiation.

My first thought on reading your initial question was that these systems covered separate areas of the building.

HVACNUT

So you have 3 heat sources in one house all serving the same area and any one of them would be fine on 90% of the heating days. Is that what we're looking at here?

If the electric rates work out for you then use the heat pump. Stage 2 for the panel rads. Maybe wire the hydro coil for use during defrost so it doesn't get lonely sitting there doing nothing.