Low temp (radiant floor) and high temp (radiator) zone control, how to run one thermostat

ThatF_inGuyInNY

I currently have a cast iron oil boiler feeding 180F water to cast iron radiators throughout the house. Some sections of the house do not have rads and they can get uncomfortable. To solve this, I am adding a mixing station and radiant floor loops. Eventually, I would like to convert the entire home, but the transition will happen over time (i.e. first cover the unheated areas, then eventually the heated areas and remove the rads). Both of my upper floors are on a single zone and im fine with this. I will be balancing each loop at the manifold to align room temp with tstat temp.

The question is, if I run a taco circ controller (SR504-4), can I just jump the R/W from zone 1 and zone 2 to kick on both the high temp circ and the low temp circ? Or is there a better way to controller both circs with a single tstat? Does it make more sense to just run both circs off a single zone on the controller? these will be 1/25hp pumps, so current draw is under 1 amp per pump

STEVEusaPA

You'd want to get a boiler control that does 2 different temperatures, with or without outdoor reset.
Primary/secondary piping. High temp can go straight to emitters, low temp needs to be mixed down.
You'll also need boiler protection (mechanically is best) to protect the boiler from low return water temperature. This is most important otherwise you'll have severe condensation issues in the heat exchanger, creating big problems.
Tekmar makes some nice boiler controls.
With oil, your best bet is a buffer tank to prevent short cycling.
Idronics by Caleffi is loaded with a ton of information-piping, controls, theory, etc.

mattmia2

You might take a look at your heat loss and the output of the radiators as well. They may have enough output and be more even at a lower temp. Since it is a CI boiler you will need low return temp protection, but you may be able to run lower temp in the radiators.

hot_rod

Yes, those micro load low temperature zones will not get along well with that boiler. Is the boiler even sized accurately to the current heat load? My guess is it is over-sized?

Properly applied a buffer could handle the micro zones, handle the two temperatures, eliminate short cycling, act as a dirt and air separator.

The Alt Source tank from Thermo 2000 also has an electric element for a dual source, should the oil side drop off. It can also be the DHW source.

EdTheHeaterMan

Original Query: Can you use one thermostat to operate two zones? In an emergency the answer is yes. As a original design, It's a crazy idea. You are asking one thermostat to make the entire first floor comfortable but you are using 2 different emitters in at least 2 different rooms in the same zone to create the BTUs for that zone. Would you use the same gas pedal and brake pedal and steering wheel (tied together by remote control) in a Tesla and a Chevy Volt and drive them on 2 different roads at the same time?

Don't use the same thermostat on the low temp and the high temp systems in different rooms and expect to get satisfactory results. What room would get the thermostat?

Thermostat wire is pretty cheep, I know, I just purchased some for a non HVAC project, last month.
Also, There are wireless thermostats if you can't get wires from one place to another.

ThatF_inGuyInNY

EdTheHeaterMan said:

Original Query: Can you use one thermostat to operate two zones? In an emergency the answer is yes. As a original design, It's a crazy idea. You are asking one thermostat to make the entire first floor comfortable but you are using 2 different emitters in at least 2 different rooms in the same zone to create the BTUs for that zone. Would you use the same gas pedal and brake pedal and steering wheel (tied together by remote control) in a Tesla and a Chevy Volt and drive them on 2 different roads at the same time?

Don't use the same thermostat on the low temp and the high temp systems in different rooms and expect to get satisfactory results. What room would get the thermostat?

Thermostat wire is pretty cheep, I know, I just purchased some for a non HVAC project, last month.
Also, There are wireless thermostats if you can't get wires from one place to another.

Its not an issue of cost really, rather simplicity. I have a 60 sq ft laundry room off of my kitchen, a 10 sq ft downstairs powder room and a 35 sq ft upstairs bathroom that dont have heat. The first two are on opposite sides of the first floor. These are my first spots to add radiant floor.

I dont really need perfect control of the temp here. I'm thinking the balancing valves on each of the loops should allow me to dial in the room temp to within a few degrees of the set temp on the first floor.

hot_rod

A thermostat is just a switch for your flow that happens to use electricity a high limit device really.

with some time and patience you can manually throttle the beast into submission. There are all levels of control logic available from mild to wild. And you can always upgrade.

ThatF_inGuyInNY

hot_rod said:

Yes, those micro load low temperature zones will not get along well with that boiler. Is the boiler even sized accurately to the current heat load? My guess is it is over-sized?

Properly applied a buffer could handle the micro zones, handle the two temperatures, eliminate short cycling, act as a dirt and air separator.

The Alt Source tank from Thermo 2000 also has an electric element for a dual source, should the oil side drop off. It can also be the DHW source.

Maybe Im missing something here but why would my micro loads matter? I am not planning to individually zone these small sections, partially for this reason. When theres a call for heat, the entire home calls for heat. Flow is throttled manually at the manifold. If one room consistently gets too hot or too cold, I can throttle the individual loop. FYI the boiler is not set up as a cold start, it maintains temp always

hot_rod

ThatF_inGuyInNY said:

hot_rod said:

Yes, those micro load low temperature zones will not get along well with that boiler. Is the boiler even sized accurately to the current heat load? My guess is it is over-sized?

Properly applied a buffer could handle the micro zones, handle the two temperatures, eliminate short cycling, act as a dirt and air separator.

The Alt Source tank from Thermo 2000 also has an electric element for a dual source, should the oil side drop off. It can also be the DHW source.

Maybe Im missing something here but why would my micro loads matter? I am not planning to individually zone these small sections, partially for this reason. When theres a call for heat, the entire home calls for heat. Flow is throttled manually at the manifold. If one room consistently gets too hot or too cold, I can throttle the individual loop. FYI the boiler is not set up as a cold start, it maintains temp always

Sure, give it a try.
You mentioned small rooms that you are adding radiant. Those will respond differently than the cast iron rads, if everything runs as one zone.