Improving air quality during rehab of tight home with no ducting
I am trying to research ERVs and air quality as part of a full rehab I am doing on my home.
The house is in Colorado, zone 5, it is a concrete dome with spray foam insulation and minimal windows, built in 1982 — I had a blower door test done and am at 1.5 ACH. The main unit is the main floor and loft with 3 beds and 3 baths, 2300 square feet. The basement unit is a 2 bed 1 bath, 150o square feet. I am installing a new radiant floor heating system and probably a couple mini splits to add a minimal amount of AC when needed. There is no ducting in the house at all, and there’s no real opportunity to add it as there is no attic and the basement will be a finished apartment without an abundance of headroom.
I have been advised I should add an ERV or find some way to improve air quality in both the basement unit and the main floor unit (2 systems). I’m hoping to get some suggestions on possible ways to implement this.
I’ve read about a system that just uses 2 fans on opposite sides of the house as a simple solution but not an energy efficient one.
I’ve also imagined an ERV system with a simple single supply, single return that would help circulate air with a very minimal amount of ducting I could try to figure out a way to route depending on ducting size required.
Is there any closed filtration system that would accomplish this, or any other simple effective ways to accomplish this while my hands are pretty tied with ducting?
I’m happy to add some floorpan photos if that helps or provide any other info. Thanks for your time in helping solve this!
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I've been using the Lunos system from 475 building supply for over 12 years in my Deep Energy Retrofits. They are over 93% efficient and only draw 12 watts each. Need to drill 6" holes in the wall. We love ours and only use the one pair for a 1,200 sq, ft. house.
Thank you for the reply Paul, I will look into these as an option.
I can install a minimal amount of ducting, but my options for routing are somewhat limited in placement options and would likely be a single intake and single exhaust. I’m hoping that something is better than nothing but would love some more help with possible gameplan if anyone else has input! Thank you.
Lunos is the only point-source balanced ventilation system I have experience with. They are effective. They aren't silent, and their fans stop and change direction every 70 seconds, which can be distracting in a quiet space like a bedroom. They have simple filters that need to be replaced regularly. They are holes in your wall that allow outside sound into an otherwise quiet house. But they are very efficient and probably the best option for a retrofit.
If you only have an opportunity for a single intake and exhaust, you will need ducting to move the air around inside the house. You could use metal spiral ducting where exposed if you want it to look good.
If you could post photos and/or floor plans, others might have additional ideas.
Sure you can use ERV's with a single supply and return, but you'll want those two as far apart as possible. I'm using this strategy on our 2 story (with basement) home. That said, for supply in your situation, Michael's suggestion of exposed/painted spiral is a good one. We used quite a bit of this in our last commercial project, and balanced correctly, it works well. In that project, the main floor (about 3800 square feet, open floor plan), used one main return with supply via exposed spiral. CO2 was monitored in that space and drove the building HRV (working with 2 air handlers) to keep CO2 in the 800-900ppm range quite effectively. In the attached pic, the spiral (on left side of pic) heads up into the floor truss area over the double door in background then comes back down into the space to cover the entire area. The floor trusses gave us about 16" to play with, hiding a few more branches off the spiral that run, hidden, across the space to service the offices on the right.
Based on monitoring CO2/VOC/Radon in our home for a few years now (1 sensor per floor), I'd focus on getting fresh air into the bedrooms as this is where the highest daily peak CO2 level (overnight) occurs.
If filtration is important, I'd look at doing this outside the ERV(s) as cost goes down and efficiency goes up with this approach.
Thank you for the replies!
I have attached a floorplan, I'm not sure how easy it will be to follow but I am thinking I might do a video walkthrough to show the space and explain what I'm working with as well. The joists all run from top to bottom of the images (north/south).
Because I will have two separate units, my understanding is that I should have two separate ERVs to keep the air spaces separate. Is this correct?
Is it possible to have a lower flowing ERV run more regularly to achieve the same result? Lower CFM fan, smaller ducting, etc.?
Is it possible to share an exhaust through the structure between a kitchen exhaust vent and an ERV exhaust vent? I'm just trying to minimize the number of new penetrations needed.
Is it possible to keep ERV duct sizing to 3"? That is the max size I could run through my 9.5" joists without requiring a soffit of some sort to fit the ducting. I'd like to stay away from exposed ducting if possible.
There should be space for two 5" or 6" penetrations through the exterior concrete wall at the basement ceiling / main floor cavity at about 2 o'clock on the drawings. This would allow for one ERV in this space which could have a short straight length of ducting run north/south inside a single floor cavity but would only get the supply and return about 1/3 of the house apart, not on true opposite sides of the house.
I doubt this is a clear explanation so I will try to get a video or two showing the space and hopefully that will help.
Thank you for your input!
The simplest is to install an ERV in your mechanical room then run the ducting across the house along the basement ceiling.
If you put the ducts above the door inside the basement bathrooms, they will not take up visually much space and will be barely noticeable. This would get fresh air to the two bedrooms and a pickup in the bath and loundry room at the end.
From this duct you can put feeds and pickup to floor registers for the main floor above to the rest of the house. Keep in mind the fresh air feed tends to be cold in the winter, so you might want to run the main floor bedroom feed inside the wall and supply register near the ceiling.
I took a couple videos to show the space in case that helps.
If there are any other questions I can answer or clarification I can provide please let me know, thanks!
Here is a walk around of the basement unit:
https://drive.google.com/file/d/1Rs61_Yur2DQM5chas1KtBwzLfmF3Vjez/view?usp=share_link
Here is a walk around of the main floor unit:
https://drive.google.com/file/d/1ttg2t6GanoHEWp-uokkQM85EK25ROSEK/view?usp=share_link
First of all, what a cool structure. I built a small geodesic dome with my Dad many years ago to serve as a paint studio “inspirational” space for mom on top a ridge at their property..some 300 feet above Lake Superior.
You mentioned the stair well is to be closed off. Is there an option to incorporate some mechanical there? It’s central, so may be a good area to look at for supply. It is a large space, and in your position, I would want distributed supply at least. You could focus on the stairway?? for main return on each floor though.
The volume to be vented upstairs is comparatively large given the dome volume up there. I’m guessing an HVAC engineer has not been involved in the retrofit so far, correct?
Thank you Dennis. I am putting a wall/door in the stairwell in the basement to separate the spaces so it will still be open to the main floor, and won’t be fully closed off anywhere.
It’s been a real challenge to incorporate a lot of these new mechanicals into this old house.
I do not have an hvac engineer. I spoke to a handful of hvac guys who all seemed very mediocre so I bought the modern Hydronics book and put a lot of time into studying and designing a new radiant heating system, and got some feedback from the heatinghelp forum. In addition to the radiant heating I plan to install two mini splits to offer a small amount of cooling (not much is needed and many homes don’t have AC here).
The remaining challenge is venting bathrooms and kitchen, and ERV. Ducting options are very limited from what I see but I am trying to figure it out.