Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit

Two Temp Radiant system and outdoor reset

DaveLDaveL Posts: 10Member
I'd like to hear some thoughts on ways to do this:
System=1 boiler (WHB Knight) w/30 Gal Buffer tank heating radiant floor system.
On radiant I'd like to run (2) temperatures {1 for tile floors & 1 for wood floors} which I plan to use thermostatic mixing valves at pumps serving the a few zone valves off each.

Certainly want to use outdoor reset ......... prefer to just use the Knight controls, should I simply reset the buffer tank temp. And set tank for min. 20F DT ?

If I do this then both thermostatic mix valves will be set-up for a higher temp than available from system until outdoor temp drops low. Not big deal I guess, when outdoor temp does drop they will be there to protect against higher temps as needed.

Is that what you wet-head residential rad folks do on these type systems ?

Or you have a better idea?

To me, ideally, if cost and complexity were not a concern, (but they are) would need a outdoor reset control on each of 2 electronic mix valves....... but don't see that as logical on residential.

Thanks in advance for sharing your thoughts.


  • IronmanIronman Posts: 5,468Member
    Are the tile floors on slab or wood?
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rodhot_rod Posts: 12,584Member
    I just upgraded one of my systems a two temperature with a Lochinvar Combi.

    I just used a manual 3 way mix valve, its' output just floats along with the ODR.

    Set the boiler at the highest expected ODR temperature, adjust the valve to the desired lower temperature, away you go.

    3 way thermostatic, as long as the ODR doesn't allow the boiler SWT to drop too close to the thermostatic setting, they are the most common, simplest way to do mix down.

    If the tile and wood are heated with plates below the subfloor, you may be able to run the same temperature? If SWT requirement is within 10- 12° of one another, really no need to have individual mix.

    Tube in mud set may need a lower SWT loop.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • ZmanZman Posts: 5,533Member
    I believe that Lochinvar has a mixing module that will run both mixing valves using onboard controls. Tekmar is another option that allows you to have indoor feedback as well.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • DaveLDaveL Posts: 10Member
    Application is gypkrete over a conditioned crawl space w/framed floor.

    Good idea HotRod, a 3 way manual/ball valve adjusted for highest temp then just let that mix ratio stay fixed and let zone supply temp float along with buffer tank temp seems logical, I like KISS engineering.

    I also agree, may be just fine with single temp, will verify once I know final decision of floor covering. From what i see it seems likely be ok as R value don't appear to be that different between engineered hardwoods and tile.

    I like the idea of mix valve at radiant pump to zones to minimize cycling, using higher DT at buffer tank cal for heat.

    Awesome forum!
  • hot_rodhot_rod Posts: 12,584Member
    Here is a valve I would consider, the manual 3 way. if you want more control, or to drive it from the boiler control and actuator can be added.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • ZmanZman Posts: 5,533Member
    If the wood vs tile is the only difference between the zones, you shouldn't need 2 temps. If there are different radiant assemblies or drastically different heat losses in the space, 2 temps is a good idea.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!