Retrofit ERV Duct Layout
Hi everyone,
I’ve posted here about air quality, radon and Co2. After 3 contractors and hours of my own brainstorming I’ve given up on a simplified ERV connected to my central HVAC system. There is no possible way to route the intake and exhaust to the exterior due to many limiting factors of my house’s design and grade.
Therefore I am moving ahead with a radon mitigation system first. But at the same time I’m trying to figure out a way of installing a separate ERV on the second floor of the house only (where we spend the majority of our hours, sleeping or working) with dedicated ductwork and bulkheads. The unit itself would be located in a closet.
Here is the design I came up with. It would be great to get feedback from those with more experience to know if this is realistic. Is installing an ERV on the second floor only a reasonable compromise for a retrofit install?
I’m also wondering about noise level of an ERV such as the VanEE AI Series (https://broan-nutone.com/en-ca/product/freshairsystems/v150e75nt). There’s literally nothing in the specs or literature about the noise levels which concerns me.
Thank you!
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Replies
I have a Broan B130E65RT (previous year's model) installed behind the wall of a powder room in a bonus space above the garage, so it's a similar setup (different floor of the house) to yours. I'm running it at the lowest speed, and the only time I even notice a slight bit of sound is when the unit first starts up, and then only for a few seconds. You might notice more noise in bedroom 4, and if so, perhaps a solid core door for the closet might help attenuate the sound.
FYI, if using separate intake and exhaust ducting for your unit is problematic, Broan does have a VTIK1 tandem termination kit that requires only a single penetration to the outside - but your airflow rate must be 110 CFM or less for that to be an option. Of course, read the installation manual to see if the restrictions would be suitable for your installation.
Thank you for sharing your experience! Sounds like running it constantly at low speed would be a good way to avoid hearing noises. Also improving the weight of the closet door would be a good way to deal with any noise if it ends up being bothersome.
I did look into the tandem termination but unfortunately there isn't even a single place for one vent out of the basement, nevermind two!
One thought after looking at your floor plan again is the fact there is only a single ERV return in the living space (bathroom) but there are four supplies (to bedrooms). This means the return will have to be able to handle the total CFM of the four supplies, which may dictate a larger diameter return duct. When the bathroom door is closed, you're restricting the air flow back to the ERV to that which flows through the gap at the bottom of the door; I suspect that is likely to result in increased noise. You also may need to add an exhaust in the hallway to deal with that potential issue and better balance the air flow through the supplies and return(s).
Thank you, that's a great point. I'll have to work on the design to add a return in the hallway... tricky since I can't make the ducts cross each other. Any suggestions?
For the supplies, I was thinking of a trunk and branch design where the supplies would step down in size as they get to the individual rooms. Would that make sense?
All of this is a lot more work than trying to figure out how to get pipes up to grade from the basement. You can then run them inside a closet, behind the fridge or inside a kitchen cabinet.
I have my supply and return plus intake filter inside a kitchen cabinet, right next to spare dish set.
Thanks - a kitchen cabinet is a good suggestion - it occurred to me also. The contractor I had at my house thought it was risky so we didn't pursue it but perhaps it's worth looking into again. There may be a spot for the fresh air intake, up from the mechanical room below the sink and out the back wall. There may also be a spot for the exhaust.
However, even if the ducting could be worked out, hooking the ERV up to the central hvac system isn't the greatest since the hvac fan will have to run constantly (noise) right? Or do you think I'd get enough ventilation with the system configured to run the fan for 20 or 30 minutes of each hour?
What is risky about a kitchen cabinet run? It is done all the time with house ducts behind a kitchen pantry.
Most air handlers have the option to set the fan speed when fan only is called. You can set this to low enough CFM that you still get decent air distribution but not enough to make much noise or use a lot of power.
20-30/hour can get you sufficient ventilation but you are running the ERV at 2x the flow rate to do it. This does decrease the efficiency 10% to 15%, so the best option is always run it continuously at the lowest possible speed to get you the right indoor air quality.
One thing to watch is during the cooling season, you don't want your fan to run all the time as it can create issues with moisture removal. This is not an issue if the system running in modulating mode but can be a problem if it is cycling. In that case, the best option is to run the ERV only in a timed mode.
Thanks, I will consider this... I'd almost just do it DIY to ensure I get the right locations. Probably hire someone with the right tools to do the brick wall penetrations though. The ducts have to be insulated right? I guess that means 6" plus 2" insulation = 8" space required for running duct?
Yes, the pipes need to be insulated. I have found that semi rigid aluminum duct with an insulation sleeve over it is much easier for these types of awkward runs and it doesn't have the restriction you get with flex duct.
Buried in the back corner of a cabinet, you will not notice the 8x8 space this takes up. The exhaust you can put through the rim joist somewhere above grade, less of an issue with it being blocked by snow and leaves.
You can rent a big hammer drill with a coring bit for the masonry or you can do a bunch of small holes in a circle with a 3/8" masonry bit and chip out the center.
Not sure I understand exactly what you are proposing - do you plan to run this duct in an attic or is your plan to install soffits (ie - by bulkheads do you mean soffits)?
I would consider 2 or 3 separate ERV's.
For the main level, get the Panasonic Whisper Comfort for $600. It only ducts the supply and return. Go through the exterior wall high on the 2nd floor in the closet between the Primary Bedroom and the Office, duct across the closet ceiling, turn down the stair wall, and install the unit on the new celing you create furring out in the stairwell. This will distribute on the the first floor.
For the 2nd floor get two ducted ERV's
a. serve bedroom 2 & bedroom 3 by installing unit and ducts in ceiling of closets between these two rooms.
b. serve primary and bedroom 4 by installing unit in primary or bedroom 4 closet ceiling. Run duct either across attic, or build soffit for ducts at EXTERIOR walls of baths where soffit won't impact headroom.
Hey, thanks for the reply, I don't think I would want to use the attic, but yes the bulkheads would be built where the ceiling meets the wall inside the conditioned space. I wasn't aware that the word soffit was used for this, but yes I think we are thinking of the same thing (described here: https://scottmcgillivray.com/frame-around-ductwork-5-easy-steps/).
The whisper comfort is unfortunately too thick for my joist cavities (7.5" actual depth) and at 2.5 sones that's pretty loud for something to be running constantly. I think I'm ok not including ventilation for the main floor since most hours are spent upstairs.
For the 2nd floor, the two unit idea to minimize ducting makes sense but then I'd need double the number of wall penetrations to the outside. How would I do the fresh air intake and stale exhausts? High and low in the closet?
Hi
I don't see why you would need to put the ERV in the exisiting joist cavities. Do you know what your current CO2 readings are? What is your other HVAC system? Is it ducted with constant air movement?
Looking at this again, I think I would use one ERV, install it in the ceiling of the primary bedroom closet. The supply and exhaust duct are on the same side of the unit so install that side of the unit facing the exterior wall. Then duct the exhaust to the bathroom, and the supply to the corridor wall. You could do this all in the ceiling of that closet and no soffits would be needed. Delivering constant fresh air to the hall should get sufficient fresh air to the bedrooms.
Thank you for taking a second look!
Re: joist cavity, I was looking at the specs on the panasonic and it looks like it's meant to go up in the joist cavity. I wouldn't want to build a drop ceiling for it. Or were you thinking that this unit would go inside a closet with the grille facing the hall?
My main central HVAC is a Carrier 38MURA / 40MUAA electric heat pump system. It cycles on and off, but it's quite efficient. I have the ecobee thermostat set to run the fan 20 mins of each hour to circulate and filter the air.
As for your new suggestion, are you thinking of the closet between the primary bedroom and the bathroom? I'm all for simplicity but I would worry that the fresh air would circulate from the hall straight to the bathroom in a short circuit and would never reach the bedrooms... Wouldn't I want to pick up stale air and supply fresh air at opposite sides of the house? Maybe I could install a single soffit/bulkhead to transport the fresh air to the opposite side of the hall? See new diagram, attached. (Note: the "X" there in the corner is a high return vent going all the way to the basement air handler.) I just worry that since the bedrooms are in positive pressure, the fresh air won't actually go into the bedrooms. But it could be sucked into the main hvac return and then distributed to the house?
The totally ducted Panasonic (ducts from exterior supply and exhaust, as well as ducts for interior supply and exhaust) unit does not have a aesthetic grill, just a metal cover you need to access to clean the filter. It could be surface mounted like a pancake to the underside of the existing ceiling in the closet, or, if there is enough space, I would mount it inside the closet over the door, and cut in an aesthetically pleasing opening over the closet door to access it.
If you are not wedded to having the ERV exhaust come from the bath, yes you could get the Panasonic Whisper FV-04v. That unit has ducts for the exterior supply and exhaust, but the interior supply and exhaust are not ducted - that comes through the face of the unit. Yes, you could install it in the closet with the front facing the hall - the challenge with this is the unit is supposed to be installed with it's supply and return ducts on the bottom. I am aware of people who have theirs installed "upside down" with the ducts at the top, and the units work fine with no issue. I'm also aware of Panasonic sending an email approving that installation, but not sure if that would hold if you have an issue. I think installing it sideways is allowed, and you probably have enough space in the closet to run the ducts up to the closet ceiling and out the exterior wall. Panasonic even has a combined supply/exhaust wall cap so you only need to make one penetration.
If you are going to install a fully ducted ERV, and build a soffit, I would build it in the bathroom, over the vanity and toilet and pull the exhaust from over the tub, and avoid a soffit in the hall. But maybe you have 9-10' ceilings and it does not matter.
I would not worry about short circuiting. The FV-04v has the supply and exhaust about 18" from each other. As long as the diffusers are properly designed there should not be an issue (they are apparently properly designed on the FV-04, and just be careful on the design if you do a totally ducted system). My FV-04V is in my laundry room, which is nowhere near a return vent, and 2 rooms away from the sleeping rooms, but if it is off the CO2 monitor in the primary bedroom shows significantly higher levels of Co2. That is why I asked what type of HVAC system you have - since yours circulates air I would not worry about it.