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Outdoor sensor

Harvey Ramer
Harvey Ramer Member Posts: 2,224
I'm convinced the only reason we put outdoor sensors outside, is because it says outdoor on the box. 

I can't think of a logical reason the sensor shouldn't go in the air intake for direct vent appliances.  I mean; maybe WWSD, but that is useless 99% of the time and is only there because it doesn't cost anything extra. 

Discuss 
BobZmuda

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 19,954
    For a direct vent boiler, it could go in the intake vent. No particular reason not to, assuming the boiler or circulator control logic doesn't need an outside air parameter when the boiler is off (such as, perhaps, a mixing valve for a continuous circulation system). However, not all boilers are direct vent...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,224
    For a direct vent boiler, it could go in the intake vent. No particular reason not to, assuming the boiler or circulator control logic doesn't need an outside air parameter when the boiler is off (such as, perhaps, a mixing valve for a continuous circulation system). However, not all boilers are direct vent...
    Good point. Some scenarios would cause a problem in the off cycle with an active heat demand. However, manufacturers could easily overcome that with a few lines of code that does a setpoint lock during those periods. 

    It just dawned on me the other day and so I tried it. It's working just fine so far. It just seems silly and irresponsible to install a sensor outside when you are bringing outside air within a few feet of the control that wants to know what temperature it is. 

    Anybody installing DV appliances knows that getting the OSS in the right place can be a real PITA. Sometimes you have to get to the opposite side of a building with no good way to do it. 

    I think for a few extra bucks a manufacturer could run with this and make it a hot 🔥 selling point. 
  • hot_rod
    hot_rod Member Posts: 17,531
    some heat could migrate up the intake also
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GGrossDerheatmeister
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,224
    hot_rod said:
    some heat could migrate up the intake also
    True. But that would only happen/matter while the boiler was off with an active heat demand. A few lines of code to do a setpoint lock during that time would solve that problem.
    CLamb
  • ScottSecor
    ScottSecor Member Posts: 617
    Not every air intake is located on the north facing wall of the building. 
    Derheatmeistermrhemi
  • ratio
    ratio Member Posts: 3,286
    The only reason the OAT sensor is supposed to go on the north side is to avoid solar radiation. Mounting it in the intake, presumably near/inside the unit, would mean perhaps a lot less wiring. I think it'd be susceptible to influences from inside the building (it'd run warm, anywhere from slightly to significantly) but I can't recall the last time I looked at a 'properly' mounted OAT sensor & not seen anything that would influence it.

    @Harvey Ramer, great idea! I've got a picture in my mind now, looks like one of those chinesium sensors that you can get on eBay, stainless & threaded to screw into a hole.

    Rich_49
  • hot_rod
    hot_rod Member Posts: 17,531


    hot_rod said:

    some heat could migrate up the intake also

    True. But that would only happen/matter while the boiler was off with an active heat demand. A few lines of code to do a setpoint lock during that time would solve that problem.

    So the boiler would need to stat to get the accurate temperature reading? But if it were reading warm for heat leaking up the intake, it may not ever start, thinking it were in WWSD :)

    I guess it would be application specific. My intake is only 5' and horizontal on a south facing wall, probably not a good candidate.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    mrhemi
  • pedmec
    pedmec Member Posts: 657
    All it would take to mess that up is to have the air intake directly over an asphalt driveway. All that heat coming off the driveway from solar gain would definitely cause an incorrect reading. Its easy enough to run a low voltage 2 conductor anywhere you want and not have to beholden to my air intake. Its the easiest part of the job.

    I think the mousetrap works fine
    mrhemi
  • Tom_133
    Tom_133 Member Posts: 836
    good topic, and some cool thoughts.

    I recently had one of those challenging boiler installs where getting the wire to a north wall was a pain if not not possible. The NTI FTVN has the wifi setup and allows you to use ITEMP so it gets your location and uses the temperature based off that location. Not perfect, but no blinking outdoor sensor, and no wire hassles. I do agree, that a boiler manufacturer could pretty simply make a sensor on the intake side that could solve 30 seconds after firing, but as hot rod said, only IF it allows the boiler to fire.

    Thanks Harvey for the exercise. I like thinking outside the box
    Tom
    Tom
    Montpelier Vt
  • ratio
    ratio Member Posts: 3,286
    There's a number of wireless sensors available now as well. I've got my eye on https://hbxcontrols.com/wav-0110.php, but it's a little expensive to get one just to fool around with.
  • Voyager
    Voyager Member Posts: 372
    Installed a concentric vent on my boiler. The intake air temp will be closer to the average temp between the outside air and the exhaust air temp. Probably can be accommodated by tuning the reset values, but for me installing the sensor wasn’t a big deal in my workshop, but in many homes things aren’t so simple.

    I am sure the obstacles can be largely overcome with software, but there may always be some conditions that are hard to accommodate in software and the performance of the outdoor reset may be compromised. And often software “fixes” like this come with unintended consequences.
  • unclejohn
    unclejohn Member Posts: 1,778
    This reminds me of a discussion we had at ABC School. Can you locate the bulb for a expansion valve at the compressor? In the case of the ODS it seems that running the blower or inducer fan for 45 seconds or so before ignition would be enough to overcome most false reading from heat sources.
  • Lance
    Lance Member Posts: 227
    I like to think. Let us say I have a sensor labeled indoor. Is it ok to put outside? I think not. Non the less, outdoor means to monitor outdoor temps, further instructions may indicate to avoid false heat and cooling effects. False means not the same as true. What do we want true, false or maybe? Many controls are designed to a certain set of algorithmic logic approaches, some customizable. Freezing temps may create a start cycle to help prevent freeze damage, such as circulator pump, or low temp maintaining even if indoor stat is satisfied. I know a client who kept his boiler off while using a fireplace to save money. Let's just say two weeks of work repairing freeze splits in the basement didn't work well. AN outdoor stat control would have prevented it. Another reason to save money buying insurance. If it says "outdoor" and I put it "indoor" and I have to explain why, well, I don't see a customer logically understanding this. And when I say to someone you need to check the outdoor sensor, where are you going to look? :blush:
  • pedmec
    pedmec Member Posts: 657
    I have the air intake temperature probe for my testo combustion analyser and have found that the temperature of the combustion air is never the same as the outside air when testing direct vent furnaces and boilers. whether its warm pvc (cpvc) from warm basement or friction of the pipe walls its definitely never read the same as outdoors.

    But to be fair i didn't wait for extended period of time as i'm there for maintenance and safety testing. Also the probe are close to the boiler for accurate temperature measurement into the boiler. I will try to test when i go to another PM and drill close to the outside wall and experiment.

    Another thought that came to me is what would happen in a warm basement and the vent material warmed up the air intake and OAT sensor during standby to the point that it might get warmer than the WWSD setpoint on the mild days.
  • Voyager
    Voyager Member Posts: 372
    Lance said:

    I like to think. Let us say I have a sensor labeled indoor. Is it ok to put outside? I think not. Non the less, outdoor means to monitor outdoor temps, further instructions may indicate to avoid false heat and cooling effects. False means not the same as true. What do we want true, false or maybe? Many controls are designed to a certain set of algorithmic logic approaches, some customizable. Freezing temps may create a start cycle to help prevent freeze damage, such as circulator pump, or low temp maintaining even if indoor stat is satisfied. I know a client who kept his boiler off while using a fireplace to save money. Let's just say two weeks of work repairing freeze splits in the basement didn't work well. AN outdoor stat control would have prevented it. Another reason to save money buying insurance. If it says "outdoor" and I put it "indoor" and I have to explain why, well, I don't see a customer logically understanding this. And when I say to someone you need to check the outdoor sensor, where are you going to look? :blush:

    It should not be hard to change the name to intake air temp sensor and avoid confusion. :)
  • Dave Carpentier
    Dave Carpentier Member Posts: 347
    Some units use wifi onto the internet to get current/forecast temperatures.
    Do they make 'wireless' ODR boxes to avoid running wires (but then you have battery issues, I guess).

    I can agree with the hassle of running a proper ODR wire, and trying to find alternatives.
    Mine will require 75 ft or so to get to the north wall.
    30+ yrs in telecom outside plant.
    Currently in building maintenance.