Taco SR504-4 or Taco SR504-EXP-4

Rickoo

Debating on the two of these. Don't think I'd ever need to expand beyond 4 zones, but it seems the EXP variant has some other added features.

The EXP is a few bucks more. Pretty insignificant. Any opinions on which to go with?

kcopp

are you installing an indirect water heater w/ a modulating gas boiler?
You would need a way to have a separate end switch for space heating and domestic water heating... exp does that.

Rickoo

No, sorry. Should have clarified. I'm adding an indirect to an oil fired Peerless WBV boiler. I'll have two zones with a unit heater and the indirect.

kcopp

Then the EXP does not really help you much...

HVACNUT

Rickoo said:

No, sorry. Should have clarified. I'm adding an indirect to an oil fired Peerless WBV boiler. I'll have two zones with a unit heater and the indirect.

What aquastat is on the boiler?

Rickoo

Hydrolevel 3250 plus. 

Dave H_2

The standard SR504 will get you what you need, control 4 circs with DHW priority.

What you'll get with the -EXP is the extra capability to customize it to your system and a few energy savings and longevity settings.
1. if you wanted to add outdoor reset to it, you can add the pc-700 control very easily.
2. The added function of pump exercising or turning on during the summer months while idle.
3. You could turn on post purge; what this does is when all zones are satisfied, the DHW zone circ will turn on and take any residual heat is in the boiler and puts it in the DHW indirect tank.

Dave H.

EdTheHeaterMan

3. You could turn on post purge; what this does is when all zones are satisfied, the DHW zone circ will turn on and take any residual heat is in the boiler and puts it in the DHW indirect tank.

This feature is worth the additional cost of the EXP version, however you will need to use a mixing valve on the DHW tank potable side. Since most mixing valves need at least a 10° difference to be accurate our will be setting the tank temperature to 130° or 140° in order to get accurate 120° mixed water out to the faucets and showers. When the excess boiler temperature is dumped into the DHW tank, it could make the water temperature go even higher... explaining the need for the mixing valve.

Some installers size the indirect tank to operate at 120° and save the price of the mixing valve. With a mixing valve, you could choose a smaller tank and actually get more DHW from operating at a higher tank temperature. So many options to choose from. Just make sure you have a complete understanding of what each part of the system does and how it relates to the other parts.

Rickoo

Being such a slight price difference between the two, I may as well go with the EXP and have the options.

My plan is to install an HTP Superstor ultra 45 with a Caleffi mixing valve. (as suggested by hot_rod) Bob Rohr. Thanks Bob!

https://www.supplyhouse.com/Caleffi-520519AC-3-4-Sweat-Union-AngleMix-Thermostatic-Mixing-Valve-w-Inlet-Checks

Keeping the tank at 140 and the mix at 120.

I was wondering of the benefits of an outdoor reset. Does it make sense on an oil boiler in the northeast? I know Hydrolevel makes one for the 3250. As I recall it was around $50. Would the $300 pc-700 be a better option?

Joe Mattiello

EXP will give you added features if you have an older boiler without reset control, you can use the SR EXP for reset, helps control injection pump if you have primary secondary, and room for expansion if you’re considering an addition. For more information on SR control, or its capability, contact Taco at 401-942-8000