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Thread: Poor IAQ - High CO2 - Seeking Recommendations for system setup ERV/Scuttle/etc

  1. #1
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    Aug 2018
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    Poor IAQ - High CO2 - Seeking Recommendations for system setup ERV/Scuttle/etc

    Howdy Folks,
    I've been fighting my home IAQ for a few years. Likely caused a lot of my own problems even Posting here for some feedback on possible options and new system configurations. I've searched or years for contractors to help with these issues without luck. Most say they don't have the tools/training and the others aren't in area or are commercial focused. Thank you for your experience!

    Issues:
    1) Increased CO2 overnight near 1200ppm, would prefer a lot lower. using Airthings waveplus devices. 1 in secondary story master, 1 in basement. CO2 is fairly even between the two sensors.
    --Does not correlate with temperature. Locking up the house, setting the furnace to 76 and leaving for a few hours didn't create a noticeable impact on CO2 levels
    2) Basement draws in cooking smells, etc from first floor (kitchen is near stairwell) even when exhaust fan is on
    3) Humidity seems to continually creep up
    3) Energy usage/bills seems to keep rising

    Setup:
    People & Pets - 2 adults. 1 raging 2yr old, a 2mo old, and a giant mastiff.
    Location - Madison WI. House built in 1990. 2 Story. Partially finished basement. 2274sq ft total. 1826 considered livable space
    Home Envelope - All new quality windows, proper insulations, air sealing. Tight home via blower door testing confirmation a few years back. Bath Vents are all probably larger than they need to be. One bath vent on first story off kitchen is hard wired to light switch (yep, i take away the should i or shouldn't I poop exhaust option for company -lol). Good exterior drainage/downspouts/sloping. Very shady lot overall. House is only hit with sun in very early morning and very late afternoon.
    Furnace - Bryant Plus 90 350MAV, installed 3-3-05
    --Was there seriously a recall on this thing? was just googling for a link to the manual.. doh..
    --had it tuned up a last winter. There was a "pinprick spec" of rust on the exchanger confirmed by pics. Contractor red tagged it and cut the wires. I put it all back together and we haven't chatted since. It's probably time to replace but I didn't care for the strong arm in the middle of the winter.
    AC - Daikin Comfort DX13SA
    --Brand new 2Ton 13Seer AC. Used to be a much larger 3.5Ton unit that would short cycle and cause high humidity.
    Water Heater - Bradford white PowerVent. Pretty short PVC run.
    ERV - RenewAire EV130
    --Exterior air (supply and exhaust) are close to same length
    --Supply air is a short run to the furnace supply air
    --Return air is a long run to the furnace return air, about 4 ft away from return plenum stack
    --This used to hooked up backwards with a DC motor continuously running and a second story bath fan on timer exhaust but the DC motor died and the fan went kaput as well. Recently reconfigured the system so that it wouldn't short circuit w/o the furnace fan. Currently controlled by % runtime switch, set to 100%.

    Humidifier - AprilAire 550 wired to thermostat. Usually set to about 40%. Confirmed working only when called for
    Dehumidifier - AprilAire 1850, set to 55% (like to run a lot)
    --Intake is about 31" away from return plenum stack. Output is basically to return very near air filter.
    --I got the whole house dehum before the new AC but the dehum still seems like it does most of the job based upon water coming out. That being said it does push hot dry air into the AC evap so I guess it tends to "win" the dehum in return air race.
    Radon Fan - Seal sump pump well
    Gas Dryer - Cruddy electrolux, properly vented into 4" rigid piping.
    Scuttle - Used to be installed before erv can re-install.
    Thermostat - Honeywell Prestige THX9000. I hate this thing...

    Thoughts from the untrained:
    -I can control CO2 in the house by keeping the furnace fan set on and the ERV at 100%. Continuous baseline is about 475-630ppm when that is in effect. It's just pricey. If I set the fan to Circulate via thermostat and the ERV to 70%, levels are too high for my liking.
    -I feel like the basement is under too much negative pressure and is pulling air downwards. I've adjusted the supplies in the basement (supply stack on unfinished partition) and try to keep some airflow in a recently built extra bedroom. There's 1 return register in that bedroom.
    -Running the kitchen exhaust fan doesn't seem to do much by itself. We always have to open a window to get air moving when we run the fan to get a good exhaust.
    -Until some of the recent balancing work, I've noticed at times air would travel IN from the second story bath vents (they are inline vented w/radon fans in the attic out through the roof) at times.
    -Picture from my bedroom IAQ meter for the last week. You can see some of the testing I've been doing to play with CO2 remediation. BTW, we've never had a CO detector go off and we have them all over.

    Couple Questions:
    -I thought the ERV would balance the house well and exchange air but is it sized appropriately to do so? Any idea how to calculate runtime for X # of exchanges and how many exchanges I should try for?
    -Should I supply extra fresh air via the scuttle?
    -Any thoughts on a manometer to gauge the pressure delta in the basement and the exterior?
    -Should I wire up any automation from the kitchen exhaust fan to fresh air or would the ERV handle that?
    -Any ideas on tests or configuration options?
    -Any recommendations on a new Furnace and control system? You can likely tell I'm a little OCD and nerdy so the more knobs the better (but I'd also just like it to work by itself, though smartly).


    Thanks much!
    Attached Images Attached Images  

  2. #2
    Join Date
    Jun 2020
    Location
    Chicago, IL
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    To answer a few of your questions:
    -A rule of thumb air exchange rate for homes is 0.35 air changes per hour. If you know the volume of the air in your home approximately, you can calculate how many CFM of outdoor air you need to achieve this. You get air exchanges via your ERV plus natural air infiltration through cracks and crevices.
    -For most applications, just use a smoke pencil to determine pressure relationships.
    -What is your target for CO2 in your bedroom at night? Is it you, wife, infant, and dog in the bedroom? Is opening a window a viable option? I'm in Chicago and I like to have a window slightly open in my bedroom for a good part of the year. What about leaving the bedroom door open to facilitate air exchange in the bedroom?

    Sorry for not answering all your questions, but I try to stay within the areas of my expertise.
    Ian Cull, PE, CIH
    Indoor Science
    Chicago, IL

  3. #3
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    Aug 2018
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    Thread Starter
    I'll have to look up how to calculate the air volume for the hole house... Thanks for the rule though! EV130 airflow is 79-165 and I guess they avg that to be 130CFM.

    My CO2 target would be always below 1000 and average less than 750. That's achievable with the current setup. outdoor air is about 400ppm I'm reading.
    Wife, I, and baby. No room for dog!

    CO2 is about the same density as regular air so it seems to pretty evenly disperse through the house as we always have our HVAC fan set to either Circulate or On to keep allergies down. Essentially keeping any window open would likely do the trick but then I deal with humidity, allergies, drafts, energy bills, etc. Too much of a princess for that.

    Thanks for the info

  4. #4
    Join Date
    Jun 2003
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    Madison, WI/Cape Coral, FL
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    What are your indoor air quality problems?

    You could make some changes to install but nothing major jumps out except negative pressure in your basement. With all of the exhaust equipment you have, like the clothes drier, kitchen hood, and bath fans, your home has a big negative air problem on occasion. We do not know about your a/c setup and the dehu should not have the warm dry air going into the a/c return. This negates the effect of the dehu when the a/c is cooling.
    These are the surface issues.

    What are you a/c return and supply temps/%RH during normal cooling? A well setup a/c should be able to maintain <50%RH during significant mid day cooling loads without the dehu running.

    You got courage posting that you live in Madison!

    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  5. #5
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    It sounds like your primary concern is your bedroom being poorly ventilated at night. High levels of CO2 in the bedroom have been associated with poor sleep quality, so I can appreciate the concern.

    I would suggest opening up the bedroom window a crack (about 1 inch) as a simple solution. If you wanted to get fancy, you could use a window-mounted ERV. You could also use your whole house ERV, but you expressed concern about the energy consumption associated with ventilating the whole house- when you are probably mostly just concerned about your bedroom where you, your wife, and child are spending the night.

    Are you concerned about CO2's direct effects or are you using that as a proxy for general indoor air quality?
    Ian Cull, PE, CIH
    Indoor Science
    Chicago, IL

  6. #6
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    Thread Starter
    So I measured the volume in cubic feet in the house at approx 15,104 ft3. 35% would be 5286.4ft3. If the erv does actually do 130cfm then that’s 7800cfh. Which seems plenty I guess. That particular erv does show range from 50-140cfm.

    However I set it to run 80% last few days and co2 builds and pops over 750 at night.

    Not sure how to measure the actual cfm. Any ideas there.?

  7. #7
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    Quote Originally Posted by Froz View Post
    So I measured the volume in cubic feet in the house at approx 15,104 ft3. 35% would be 5286.4ft3. If the erv does actually do 130cfm then that’s 7800cfh. Which seems plenty I guess. That particular erv does show range from 50-140cfm.

    However I set it to run 80% last few days and co2 builds and pops over 750 at night.

    Not sure how to measure the actual cfm. Any ideas there.?
    750 PPM CO2 in home is very good. How many occupants?
    Wind and outdoor temperature last night?

    Keep us posted.
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  8. #8
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    Thread Starter
    2 adults, toddler, baby + mastiff

    some pics showing my testing and readings attached. careful on the scales as they aren't all uniform.. i'm happy with 750 CO2 and I can keep right there or under now that i've re-ducted my ERV to installation instructions. but i have to use the furnace fan at 100% and the ERV at 100% to do so and it doesn't seem to be making-up air from all the ventilation. I'm not positive if it can be configured to balance the air (supply more than it takes out). now that i can post links.. this is the manual: https://www.renewaire.com/wp-content..._016_JAN20.pdf

    i'm sure running 100% Fan & ERV is going to cost me some dough each month. so my goals are to keep the baseline that I have and try to dial it back and see if i can fix the negative pressure in the basement.

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  9. #9
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    As far as your VOCs and CO2 goes your readings are very good.

    BUT - I would allow a Big (possible very big) fudge factor for accuracy of your Air Things thingy.

    For VOCs I'd recommend https://www.homeaircheck.com/products/.
    Will cost between $130 - $200 per room but will provide a much closer estimate.

    For CO2 I'd recommend CO2meters.com.

    The numbers, as they stand, are very good - I've been struggling for years (unsuccessfully so far) to get numbers like yours

  10. #10
    Join Date
    Oct 2020
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    From reading your post, you have concerns with CO2 levels (which temporarily pop up), and then energy/cost of running the ERV at 100%.

    One solution would be to automate your RenewAire EV130 ERV so that the CO2 levels trigger the ERV on/off (duty cycle) or from normal speed to boost speed. There are some emerging methods for doing this.

    I'd also be curious to know if you experience issues in winter AND summer as that may be a clue (i.e. outdoor T/RH/dew point, stack effect, infiltration).

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