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Community and Q&A

Confused about ERVs

DavidLLarsen | Posted in General Questions on

I am a builder in the mountains for North Carolina and am in the process of building my personal house. I’ve never had an ERV nor have any of the houses I’ve built. I’ve seen the light and want one. The house is about 2400 sqft over three floors. it’s 2×6 construction with spray foam in the roof, at the bands between floors (batts in the walls and between floors), and pretty efficient  windows/doors. Its got two HVAC systems, the first floor will have a  heat pump with gas back up and the same for the top two floors. It’s 4 beds/3.5 baths. The HVAC guys are just now starting rough-in so I need to decide ASAP!

My HVAC installer while OK for most systems is in the dark as much as I am about ERVS. He wanted to install a single Broan ERV70s on the 3rd floor with a single dedicated return and a single dedicated fresh air supply. 

I’d like a fully ducted system. After calling Broan I’m leaning towards the ERV180s but I’m open to suggestions. How many returns should I have for the stale air? I was thinking at a minimum one in the kitchen (1st floor) one in each of the two main bathrooms (middle floor) and then on high on the 3rd floor with a return of fresh air in a central location on all three floors.

Any thoughts/help would be greatly appreciated

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  1. walta100 | | #1

    My opinion, only do the EVR if you have done a blower door test less than 1.4 ACH.

    Were you able to keep the duct work out of the attic? If so and the top floor has a flat ceiling I say skip the spray foam ceiling and fill it cellulose

    If you can get city gas skip the heat pump, if no city gas skip the gas furnace and use a high end heat pump with electric back up. The heat pump will be good to about 8° you will have very few hours when the electric runs.


  2. DavidLLarsen | | #2

    The 3rd floor living space has vaulted ceilings which is why we are spraying foam under the roof which has the added bonus of having our HVAC system and erv in conditioned space.

  3. Expert Member
    Peter Engle | | #3

    You are on the right track with your design. It is generally best to exhaust air from the rooms that generate the most pollutants. Kitchens and baths are typical. Some people prefer to send the fresh air supply directly to the bedrooms where it is most important, but in some homes, this cooler air in winter and damper air in summer is uncomfortable. Providing fresh air in a central location (stairwell?) is probably a good alternate.

  4. Expert Member
    AKOS TOTH | | #4

    Based on the number of rooms you are looking at around 100cmf erv. The house is larger and it is usually best to have some boost capacity, so between 150 to 175 cfm is a good target.

    As Peter said, usually best to deliver fresh air directly to the bedrooms, so some dedicated ducting, but you can save a bit by sharing the return air duct with the furnace. Just make sure the return ducting is sized properly as you don't want much pressure drop to unbalance the erv.

    I recently saw a high velocity AC install (spacepac), the small flex ducts for that would make excellent ducting for the supply as it can be run inside standard stud walls. Not cheap but much less labour.

    For the ERV unit, look for one with an ECM blower. Since this is running 24/7 the power savings pay for the up -charge in a couple of years. I like the Panasonic intellibalance units, they are not too expensive but have great specs. In your case you would need two, so there are probably cheaper larger units.

    If you don't run dedicated ducting, the furnace needs to be interlocked with the erv. This works best if your furnace has an ECM blower with a low fan only speed. A regular blower will consume way too much power if it has to run all the time. This setup is always a bit of compromise, thus always best to have dedicated ducting.

  5. DavidLLarsen | | #5

    Bit of an update. Just met with my hvac installer. To get an exhaust vent near the kitchen will require a run of between 70-80’ including many bends which concerns him. At this point, would it be better to go with a Broan ERV70 on the third floor and one in the basement? There’s not much price difference between two 70s and one erv180. I understand we’d have more maintenance etc but wouldn’t it be more effective to greatly reduce the runs?

  6. this_page_left_blank | | #6

    You want supplies in all the bedrooms, and the main living areas. With the layout of your house, I would go with two units.

    The ERV70 is not big enough, not even with two of them.

    The efficiency of both the ERV70 and ERV180 is poor, with the ERV180 being especially awful.

    Browse through the HVI product listing, and sort it by sensible recovery efficiency (SRE). Don't even bother looking at anything below 70%. Also ignore the apparent sensible recovery (ASRE), and be wary of any manufacturer that advertises using this spec. It's deceptive marketing. Make sure that the device you select has a boost function.

    How many people will live in the house? This will partially determine the required CFM of fresh air.

  7. Expert Member
    AKOS TOTH | | #7

    The two unit might make sense in this case. You might be able to save a bit of ducting cost by only doing dedicated ducting the unit supplying the bedrooms.

    For the main floor unit, you can share the air handler ducting as in Fig 4.1:

    I think for simplicity and maintenance perspective, I would try to figure out how to use a single unit though. A Broan ERV140TE flows the same as two E70 but uses 1/2 the power. Instead of a kitchen pickup, might be simpler to run a duct to the return of the main floor furnace.

    P.S. length of the run doesn't effect losses as much as bends. 80' of 5" duct with a couple of elbows with at 60CFM is only 0.15" pressure loss, well within the capability of most ERVs. Just don't use flex.

  8. DavidLLarsen | | #8

    There will be 4 people living in the house

  9. DavidLLarsen | | #9

    Thoughts on the Panasonic Intelli-Balance 100?

  10. this_page_left_blank | | #10

    The Intelli-Balance seems like a nice unit.

    One of the benefits of having two units is that you could have one supplying the bedrooms, and the other the main living areas. I've noticed that if everyone is the main floor living area the HRV has to be set at almost double what it is when everyone's asleep in separate bedrooms. The rate of mixing seems to be too slow. I imagine it would be worse with three floors.

    Using the ASHRAE 62.2 standard, your house needs (4+1)*7.5+2400*0.03=110CFM. In my personal experience, it seems like number of people is more of a factor than size of the house, but that's a reasonable number to start with. Your equipment should have about 100% overcapacity for boosting (on a timer to remove humidity from bathrooms or fumes from the kitchen, and as an override to accommodate gatherings of people.)

  11. ColbyForester | | #11

    I am also looking at putting two ERV's in my house. I have looked at the Panasonic units and like them but they do not have a boast function. I would like for them have a boast function to be able to replace the bathroom fans.

    Has anybody used or looked at the Fantech line of ERV's? They seem reasonably priced and also has a boast capability.

  12. DavidLLarsen | | #12

    So after hours of research, I like the sounds of the Panasonic FV-10VE1. Problem is that it's not big enough for the whole house. Worst case, I need two. Any thoughts abut using one for the top two floors where the 4 bedrooms and and the two most heavily used bathrooms and maybe a whisper green or even a Panasonic FV-04VE1 in the laundry room which is located between a bathroom and the kitchen? Just trying to control my sky rocketing build cost on this project!

    1. Expert Member
      AKOS TOTH | | #13

      The spot erv a good option, I would put the spot closer to the living space, maybe the halway to the living room, or even better in the living space (or near main floor furnace return). You want it the open space, so the fresh air can circulate.

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