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temp settings for staple up radiant

I retrofitted my house with a staple up radiant system and i am using a munckin contender boiler to heat it. The house is about 800 square feet evenly split into 7 zones that will all run off of 1 thermostat. Origionally i was using a waste oil boiler set to 150 degrees with a mixing valve to temper the water down to 120 for the floors.

With the contendor will it be more efficient to set the temp to say 150-160 and temper it down with the mixing valve and let it cycle on and off or should i set it to 120, ditch the mixing valve and just let it run constantly?

thanks for any help!


  • CMadatMeCMadatMe Member Posts: 3,066
    Radiant Control

    I think you mean your house is 7 loops of radiant all on 1 zone.  The contender does not have out door reset out of the box so I would make sure I use a mixing valve. From your radiant heat loss and design you should have a water temp that you need at your design temp to heat the space. In laymen  terms, you need xxx degree of water temp to heat the space to your setpoint temp (70) for most people in most cases at 0 degrees unless you live in a climate that has a colder or warmer design day. A modulating mixing valve will allow you to set a heating curve for the radiant. Munchkin does offer a control package for this. It is called Vision 2 and can be added to your boiler. You really need the valve not only for your comfort but as protection for the floor.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • jaydiemmejaydiemme Member Posts: 13

    your right i meant to say 7 loops. I am using a old grunfos manifold with the zone valves removed. I did my heat loss calculation and came with 120 degree water for the floor. Assuming i am going to stick with a manual mixing valve what water temp and differential should the contender be set at? When i set it at 180 with a 30 degree differential it heats up quick and cycles about every 10 minutes. If i set it at 140 it seems to stay running longer. Am i correct to assume that because it is modulating it should be more efficient running constantly rather than cycling on and off?
  • WojoWojo Member Posts: 7
    Floor thicknes

    How thick and what material is your flooring? Are your joist spaces insulated properly? I have done staple up jobs and have found I have needed to run 160 or more even up to 180 on floors up to 2 inches thick!
  • jaydiemmejaydiemme Member Posts: 13

    the floor is only 1 inch of plywood subfloor and about 3/8 of engineered hardwood.With the water at 120 the floors have been at about 75-80. I cant believe that you need 180 degree water to heat up any floor. Ive got bubble foil insulation r 13 under the tubing so most if not all of the heat goes to the floor

    120 degree water is working fine to keep the house warm. I just need to know what temperature the munchkin should be set at. Im trying to set it up as efficient as i can with what i have. I dont mind manually adjusting the mixing valve if it does get colder and i need hotter water in the floor but i am confused as to how to set up the munchkin.
  • Mark EathertonMark Eatherton Member Posts: 5,837
    Set it and forget it....

    There is NO advantage to setting a modcon boiler high, then mixing it down. Set it for the lowest allowable temperature you can get by with and let it rip.

    If you can heat your home comfortably with 120 degrees F, it indicates to me that your heat load per square foot is fairly low. My experience echoes the others, requiring temps closer to 180 degrees to make it work, but your milage may vary.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • jaydiemmejaydiemme Member Posts: 13

    thanks for the response thats the answer i was looking for. Its a small house with few windows and lots of insulation. Since i have no way to regulate the water temp ive set it to 120 and was able to keep the house at 68 on the coldest days, this was using a waste oil boiler that never shut off but i didnt care because the fuel was free. Now that i am paying for propane i want to conserve it. For now i will have to deal with any adjustments on the fly as i dont have the funds to add the vision system right now.

    Any insight on the differential? let say i only need 120 water should i set the boiler to 120 with a 10 degree differential?

    thanks again everybody.
  • CMadatMeCMadatMe Member Posts: 3,066
    Strongly Disagree

    He has no protection of the floor in case the boiler runs a miss plus he doesn't need 120 all through the heating season only on his design day. At min if he is going to use the boiler as his mixing valve he shut put an aquastat on his supply as protection to shut down the boiler in case of a ramp up of water temp. Will it work yes, will it tend to overshoot comfort yes.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Mark EathertonMark Eatherton Member Posts: 5,837

    Chris, you are allowed to disagree with me :-)

    However, during the last 10+ years of installing modcon boilers, I can't think of ONE heating only, single temp system where I installed an additional mechanical aquastat on the system to protect anything...

    Now, in your jurisdicitions, the AHJ may require the use of a good ol' mechanical aquastat because they (or you) don't trust those new fangled solid state controls, but I can count on all my toes and fingers, the number of failed aquastats that failed in the CLOSED position....and caused a dangerous situation.

    On the other hand, out of the many hundreds of new fangled controls on mod con boilers out there, I have not had ONE unsafe failure of the solid state controls, not one.

    Now, I didn't offer the advice to the consumer about doing an outdoor reset control, because that wasn't his question. He wanted to know if he had to set the boiler for a higher temp, and mix down, or if he could set the boiler control for a lower set point and be done with it. Besides, unless he is a card carrying, certified HTP dealer, he CAN'T get the necessary items to do an out door reset on his boiler. Now, I am positive, SOMEONE has figured out a way around that provision, but he asked a simple question, and I gave him a simple answer.

    Good thing he didn't ask whether a Viessmann was better than a Munchkin eh...

    Peace, out.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • CMadatMeCMadatMe Member Posts: 3,066
    Peace Out

    I always urge on the state of caution. I know he can't get the Vision package and you did anwser his question. We all know the anwser to the last question. :) Shoot that Matsui just hit a homerun...I hate those damn Yankees
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Mark EathertonMark Eatherton Member Posts: 5,837
    To Jay re: Differential setting...

    Sorry for having to reply on RadWiz's post, but the link to reply to your post gives me an error, OOoops, that page doesn't exist.

    If memory serves me correctly, the differential on Munchies is split around the set point, so if you want 120, and you have a 10 degree diff., then it will cycle off at 125 and on at 115

    Deeper differentials allows the internal logic to smooth out the boiler operation, meaning it has a better chance of turning on and staying on, which is the most efficient operation of the appliance. Having a small differential usually causes short cycling, which is not good for the appliance, or all the components connected thereto .

    The Munchie comes from the factory with a "Bottom Up" logic as it pertains to burner firing. When first called, it goes to a higher RPM for firing, but once flame is confirmed, it drops down to its minimum burn setting, and then slowly increases RPM's in step stages until it approaches its fixed set point, and it then starts modulating to maintain the set point.

    Most older North America boilers did the exact opposite. On a call for heat, they'd go to high fire, then idle back as they approach set point. Unfortunately, they are NOT capable of modulating. This causes them to short cycle a LOT. Attempting to apply the Euro logic of ramping up slowly could cause a shortage of heat, for whatever purpose it is being used for. THis continuous short cycling is what causes the boiler to be inefficient seasonally. The only time it is correctly fired, is less than 2% of the time (design conditions).


    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • kcoppkcopp Member Posts: 3,598
    I have many...

    times designed the entire system Radaint w/ panel rads to run off of 1 temp... using a condensing boiler... keeps it simple, both for now and the future. The Munchie can handle that fine. If it were a conventional Cast iron boiler, that would be a diff. story.

    The other thing I noticed it that you use Bubble foil insulation alone...True? You would be much better served to add real insulation..fiberglass, foam to drive the heat up. the buuble foil junk can't do that. Your basement will be much cooler.

  • jaydiemmejaydiemme Member Posts: 13

    my floors are 2x6 so i have bubble foil insulation with r13 below it which leaves me a little bit of airspace for the pipe.

    I have set the munchkin to 145 with a 10 degree diff and it have been running great. The return water comes back around 135 and the munchkin will keep the outgoing water right at 145 without turning off. Im hoping with is the way to run it for maximum efficiency.The only problem i am having is the gas valve vibrates wildly sometimes when it fires up. I will have to call the gas company back to take a look at the pressures again.
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