Questions regarding ERV retrofit installation
I'm trying to solve a persistent issue in my 1973-era, hydronic baseboard-heated home in New England which has been bugging me for some time and is going to get worse.
A couple of years back, on a hunch, I built a couple of CO2 sensors and connected them to my Home Assistant deployment to track CO2 levels in our bedrooms, and discovered that when the doors were shut at night, the CO2 levels skyrocketed, between 1500 and 2500 PPM depending on the number of sleepers present. The "fix" for this was pretty straightforward; keep the doors open! This worked well for a year or two. My oldest is starting to want more privacy and has been shutting the door to her room and I expect this to continue on with my other children as they get older.
Since the house has no ductwork I have been at a loss as to how to solve the problem, but after reading up on ERVs it appears that installing them with dedicated ductwork is both supported by manufacturers and recommended by some groups like GreenBuilding Advisor.
My two questions:
- Would installing ductwork for both intake and return air in each bedroom cause issues? The primary reason for this is that cooling in the summer months is through window ACs. Putting the intake in the recommended areas (kitchen, bath) would result in hot air being returned into the cooled room, which would drive up the cost to keep the rooms cold.
- My ONLY option is to install the ERV in the unconditioned attic. Manufacturer opinion on this seems split. Carrier indicates that their ERVs can be installed in unconditioned spaces provided that the ductwork is insulated. Panasonic (my preferred vendor) states that their units can only be installed in conditioned spaces. My plan has always been to run insulated flexible ductwork in the attic to each room. Provided that I do use insulated ductwork, will ERVs function in unconditioned spaces?
Comments
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First things first. An ERV or HRV (I much prefer HRVs, as they don't recycle odoours and some contaminants) requires both an air source and an air return to be effective in a space. If you take a room — or other space — and have only a feed or only a return, you'll get very little circulation in the space. Therefore not only will installing both supply and return ducting in the bedroom — or other space — you have to have it unless you keep the doors open.
Second if the unit and ducting are in an unconditioned space, you will need to use very heavy insulation on everything.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Besides efficiency, the big issue with attic ERV, is you have to get up there to change filters. This might not sound like a big thing, but it will eventually be left. I have mine buried behind a closet so it takes a fair bit of unpacking to access and it is currently two filter changes overdue.
I would find a spot inside the house that is accessible. This also avoid any of the attic temp issues that will be hard on any equipment. You can still run some of the ducting through the attic if needed. The top of a closet near the bath is a good spot for it.
There are very few places that you can comfortably live now without AC. I would look at getting ductwork for that added in first and then figure out how to connect the ERV to it. Generally with older houses, once you have air circulating through the rooms, the house has enough outside air leaks that and ERV might not be needed.
@Jamie Hall ERV is now the recommended recovery for almost all climates. In colder climate it reduces how much humidification you need in the wintertime and in the summer it helps reduces the latent cooling load. As a bonus for the OP, an ERV doesn't need a drain that could freeze up in the winter if the unit is in the attic. I run an erv and cooking sometimes can spike VOCs especially after deglazing a pan with wine. Even though some of those VOCs can cross over inside the core, the house air returns to normal quickly.
In terms of returns in bedrooms, any amount of undercut needed to clear carpets in the doors works. The air flow we are talking about is 10-20CFM which is pretty much nothing. You can have a central stale air pickup in the bath with fresh air supply to each bed. Keep in mind that with dedicated ducting the ERV supply will be slightly colder than house air in the winter and slightly warmer in the summer.
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ASHRAE wants a complete air change every 3 - 4 hours throughout the structure. During mild weather will that ERV do that?
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If it is running, of course. Say you have a 14x14x8 bed, so 1500 ft^3. At 10 CFM an air change every 2.5h.
The ASHRAE 62.2 ventilation needs are generally are in the ballpark.
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I am less concerned with things like VOCs and odors given that this would be exclusive to the sleeping spaces and not in places like the kitchen. This home has no natural gas / propane cooking appliances FWIW, all electric. When you say "very heavy insulation" would this be something greater than the pre-wrapped 4" flex ducting with R6 insulation?
I'm aware of the need to change the filters 😫… but this is one of those fun-sized 4 bedroom homes with about 700 square feet total on the second floor. There is a single closet outside of the bedrooms that measures about 2' x 16", nowhere near enough to fit the unit let alone the minimum 2' required straight-run ducting out of the unit itself. It has to go in the attic, which is actively used for storage so we aren't strangers to it. There's plywood flooring spanning the center of the space so we will be able to get to the unit without much clambering. As for the next owner, they will have to fend for themselves, unfortunately. I'll probably end up training the kids to do it.
As for ductwork for air conditioning, I have gone back and forth on this and the cost is just not justifiable. I've seen estimates in the 20-30k range and frankly, I will just haul window units for that price.
Highly doubtful and I am really not concerned; this is about harm reduction, less about standards adherence.
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I agree with @Kaos on the fact that ERVs are now the preferred approach in most climates. I was just stating that i disagree… as in the process of retaining latent heat, they also retain a large fraction of any water soluble or polar air contaminants that might be present. Which, to my may or thinking, rather defeats the purpose of the air changes.
But then I also recognize that in a good many settings the outdoor air quality is actually not much better than the indoor… sigh…
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Yeah, with all of the wildfire air quality notices we got last year, I'm included to agree.
Edit: This article seems to agree that HRVs may be a better choice in New England. In particular, this piece stuck out to me: "A modest home with one or two occupants provides much less internal moisture than the same home with four occupants, two dogs and a cat. The low occupancy home may want to retain moisture by using an ERV, while the higher occupancy home may want to use an HRV due to higher levels of moisture from high occupancy."The house is generally filled with 5 people, 3 cats, which seems to qualify as "high occupancy".
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That is only true if the house is tight, this is pretty much never the case with older homes. Unless you are currently running a dehumidifier in the winter, ERV is the better choice. ERV still removes moisture in the winter but significantly less than an HRV.
@Jamie Hall Residential ERVs have a membrane core not a spinning enthaply wheel like commercial units. Pretty much like an HRV, there is no significant cross over between stale air and fresh air.
@skybolt_1 The work to install an fully ducted ERV is pretty close to an air handler. BOM cost is also not too far off. If you are comfident enough to install an ERV, a slim ducted unit is not far off and gets you both airflow and cooling. You can look at something like a MrCool DIY which has quick connections for the refrigerant.
https://support.mrcool.com/hc/en-us/articles/43552971347860-24K-MRCOOL-DIY-Hybrid-Air-Handler-230V
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OK, good to know about the HRV vs. ERV. They seem to be priced similarly, but the issue with HRVs that I didn't like was that they require a drain line (which will absolutely freeze, issues, etc.)
I would love to install an air handler but I am super constrained in the layout of the house, where it would sit, etc. It wouldn't be feasible to DIY this as I'd need to get lines run from one end of the house to the other plus run 220 up to the attic… it's a much larger project than I'd be able to take on I think. But maybe I'll run through some sketches to see if there are any options I'm missing.
Would R6 insulated ductwork be sufficient for this? Based on this website it appears that R6 is the standard across all zones for unconditioned spaces.
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