Pennsylvania Waterfurnace Series 7 Duct Work Condensation

Discussion in 'Maintenance and Troubleshooting' started by stevelion, Aug 15, 2021.

  1. stevelion

    stevelion New Member

    I had a Series 7 installed on 2015. Around 3 years ago, I noticed water marks in the kitchen ceiling in late fall/early winter. It looked dry, but I cut hole in the ceiling to look around and it did look dry. Noticed the HVAC duct work in this bay, closed it up, patched and repainted the ceiling. Within a year, we noticed water spots all ever the ceiling and initially suspect it might have been a leak from the upstairs bath, but found nothing definitive after a bath remodel this past year. It occurred again a few weeks ago and again last week and so I finally opened up the ceiling and found the culprit. i.e. the supply duct to an upstairs bedroom is dropping condensation all on the ceiling the length of 20' run. We had high heat (95 f) and humidity last week over several days. I never head this problem prior to the geo system installation.

    I pulled up the Symphony system and I see supply air as low as 38 f and so I'm thinking this is way too cold and the possible source of the problem. Looking for input.
  2. SShaw

    SShaw Active Member Forum Leader

    I've had some issues with condensation on the outside of my 7 Series supply ducts as well. I've only noticed it at the unit and on a couple supply registers. I've improved things but haven't completely resolved it yet.

    Here's a couple things to think about:

    1. The 7 Series has "active dehumidification." This will run the compressor at stage 9 and modulate the fan at a low speed, like 3 or 4, to keep the coil just above freezing. This will give you the ~38 degree supply air.
    2. The humidity sensor in my 7 Series TSAT reads high by about 16% compared to a calibrated sensor. This will cause the active dehumidification to run when it shouldn't be running, leading to more run time with very cold supply air.
    3. You can program an offset into the TSTAT, but it only goes to -10%. So, mine still reads about 6% high.
    I had my dealer come out last year to look at the issue. He said he was dealing with sweating units at his own house and with other customers. He got on the phone with Waterfurnace and told me they confirmed there was an issue they were looking into. The dealer said he'd let me know once he heard a resolution from Waterfurnace, whether there was a firmware update, etc. I never heard anything back from my dealer but that doesn't mean much. I'd likely need to remind him before he'd get back to me.

    The dealer plugged some sizable hidden air leaks in the supply and return ducts at the unit, which helped. I also programed a -10% humidity offset into the TSTAT and adjusted my humidity setting up by the remaining 6%, which seemed to help too.

    This summer I installed a portable dehumidifier near the unit, just to see what it would do. With that set on 45% I've only seen water dripping maybe once all summer. The portable dehumidifier costs about as much to run as the 7 Series though, so it's not a great solution.
  3. stevelion

    stevelion New Member

    Excellent information - thanks you for the response. Your active dehumidification answer explains why I saw the fan at 4 while the compressor was at 9. The tech that stopped by today said that the fan speed should be higher based on on what he was seeing in the AID tool. Perhaps he was not familiar with this setting.
    Last edited: Aug 20, 2021
  4. SShaw

    SShaw Active Member Forum Leader

    The 7 Series is complex, so it's possible the tech isn't familiar with all the details.

    His comment that the speed "should be high" isn't clear. The 7 Series allows you to set the speeds for constant fan, AUX, and the high and low limits during compressor operation. There's also an offset (-15% to +5%) for fan speed in cooling mode. Except for dehumidification, the actual fan speed when running is interpolated between the low and high settings, based on the compressor speed.
  5. stevelion

    stevelion New Member

    I edited an error in my post. I meant to type " should be higher" as in higher than a fan speed of 4.
  6. SShaw

    SShaw Active Member Forum Leader

    That comment makes more sense, especially if the tech is not familiar with the dehumidify feature.
  7. stevelion

    stevelion New Member

    So I noticed more condensation today and attached a photo that was taken in my basement where I've never before noticed condensation, but it was so bad, I saw water on the floor beneath the duct. I also took the attached Symphony screen shot a few minutes after observing the condensation. I have two other cheap humidity sensors that read 27% and 40% while the WF thermostat reads 50%. The dehumidification setpoint is currently set to manual at 45%. I'm no HVAC expert, but the Delta Ts just seem outside of normal range and your theory on the accuracy of the humidity sensor is probably worth looking in to as well. The EWTs are not that great either in my opinion. Thanks again for your help.

    WFS7 Symphony Screenshot 2021-08-24  sn scrubbed.png

    [​IMG] HVAC duct with condensation.jpg [​IMG]
    Last edited: Aug 24, 2021
  8. SShaw

    SShaw Active Member Forum Leader

    Your images didn't seem to come through. See if you can try posting them again.
    stevelion likes this.
  9. SShaw

    SShaw Active Member Forum Leader

    The EWT looks fine for August. That's a lot of condensation though.

    It's very likely your thermostat humidity reading is way off like mine is. The system cannot work properly in that case. Setting the thermostat at 45% is trying to get the humidity down to something like 30%, which is impossible, and will just make it run almost all the time with that extremely low leaving air temperature, which will cause the ducts to sweat.

    Inside humidity of 50% is fine. You don't need it at 27% or even 40%.

    I would disable the dehumidification feature on the thermostat and see how it does. I'm betting it will dry up a lot.

    You'll get long runtimes with the variable speed, so the humidity in the house should still be in a comfortable range.
  10. stevelion

    stevelion New Member

    I just disabled and will give that a try. I let my dealer know that the issue is occurring and provided the humidity values from the other sensors and will see what they say. After disabling the dehumidification feature, the Delta T looks better already. With cooling at 9 and fan speed 9, the supply air is 46.9 deg f vs return air at 70.5 deg f (the thermostat is set lower from 75 to 70 in the evening too). Thanks for your assistance.
    Last edited: Aug 24, 2021
  11. stevelion

    stevelion New Member

    So it's been about 14 hours since I changed the dehumidification off and I just checked the duct work and it's bone dry even with an outside temp around 88 deg f and humidity at 59%.
    Last edited: Aug 25, 2021
  12. SShaw

    SShaw Active Member Forum Leader

    Sounds good.

    Setting the thermostat too low can contribute to condensation also. I usually keep mine on 74, but will occasionally set it to 72 for sleeping.
    Deuce and stevelion like this.
  13. Jamie V.

    Jamie V. New Member

    I have had the condensation problem every summer since my Series 7 was installed. I ended up just setting up a protable fan to blow air over my ducts and that seems to solve the problem. I'm going to turn off dehumidication as suggested above and see how that works.
  14. SShaw

    SShaw Active Member Forum Leader

    I ended up placing a portable dehumidifier in my basement near the 7 Series and letting it drain into the condensate pump. That seems to have solved the problem and it dehumidifies the whole house. Running the dehumidifier costs more per month than the 7 Series though, so it's not a great solution. A portable fan would probably be cheaper.
  15. gsmith22

    gsmith22 Active Member Forum Leader

    don't know if either of you have a hot water heater nearby in your baseemnt (a common thing for desuperheater setup) but a heat pump hot water heater willl not only dehumidify your basement but you'll get hot water too. two birds with one stone
  16. Deuce

    Deuce Member

    I am a retired builder of custom beach homes and the problem is not the system but the air around the ductwork is humid and you need better insulation around the ductwork to protect it from the humid unconditioned air.
  17. gsmith22

    gsmith22 Active Member Forum Leader

    Insulate the ductwork and dehumidfy the air. might as well get hot water from dehumidifying with a heat pump hot water heater (if your water heater is in your basement)
  18. SShaw

    SShaw Active Member Forum Leader

    The 7 Series does contribute to the problem, as discussed earlier in this thread. The "active dehumidification" mode unique to the 7 Series lowers the fan speed so much that the air leaving the coil is in the mid to high 30s, which is far colder than the supply air from a typical AC system. Supply air that cold is far below the 54F dew point of typical indoor air at 74F and 50% RH. As also noted above, the humidity sensor in the 7 Series (mine anyway) is reading significantly higher than a calibrated sensor, which activates the dehumidification mode more than necessary.

    I considered a heat pump water. It isn't a great solution for me. They all seem too tall for where my system is located, the basement is already cooler, and it would only dehumidify when the unit was heating water.
  19. gsmith22

    gsmith22 Active Member Forum Leader

    I don't doubt you considered it and certainly the height thing is a real issue. I have an 80gallon bardford white HPHWH that is 73.5" tall per the unit specs. I have a pretty tall basement and there isn't a lot of room above it for the connections so its certainly something to be consider.

    But, on the "basement is cooler, only dehumidify when unit is heating" aspect. Consider how these things function in tandem with your geo desuperheater(s). Other than if my kids and wife all decide to get back-to-back-to-back showers (not that common), the HPHWH runs very little in the spring and fall and never runs in the winter because the desuperheaters from my geo units are cranking out so much hot water. Different situation during the summer when desuperheaters don't run and HPHWH is doing all the hot water heating. So the HPHWH is mostly running when you are very likely running geo in cooling mode and when your basement is its hottest/most humid (ie during your periods with the condensation issues being discussed). Its a really symbiotic relationship that turned out far better than I had planned.

    My system has 2 geo units, both with desuperheaters that feed a 50 gallon buffer tank that in turn feeds the 80 gallon HPHWH and I'm in a heating climate. I think the functioning would still hold true if I only had 1 geo unit too. All the HPHWH units I have seen are hybrid allowing you to select heat pump only, heat pump+electric, or electric only so if the heat pump running in the winter was really a problem, could always switch it to electric only then and have what you probably have now. Now, I wouldn't go out and replace a functioning electric hot water heat with a HPHWH but when it came time to replace, I think its a no brainer. Especially if state rebates are available.
  20. rjstevens

    rjstevens New Member

    This is awesome information! I had my Siries 7 water furnace installed a couple of years ago and it has run flawlessly. Routine maintenance twice a year just to have a check up, and the technician turned on the dehumidification last fall. This has led to me having condensation on my duck work. I was wondering why my compressor was running at nine and my fan speed at two. Thanks for the info!

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