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.
Thank you Akos, I really appreciate you taking the time to look at this and try to point me in the right direction.
I put this aside for a while but now need to get all of my HVAC done before I can move forward.
I’m fully willing to hire someone to help with the hvac / ducting design but the hard part seems to be finding someone who knows what they’re talking about key tanks abnormal home.
I need to decide on ERV as well as 2 kitchen and 4 bathroom exhaust vents, and 2 dryer vents.
If this is something that can be designed remotely I’m wondering if I may be able to find help with this from within this group. Would you be willing to chat more about it? Or would someone else who feels they can help? Thank you again, this forum is an amazing resource!
Hi Akos, hoping you’ll see my reply above. Trying to contact you and Dennis to discuss this more if possible. Please reach out to me at [email protected] thank you.
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.
Hi Dennis, I am revisiting this all now and it is time to make progress here so I can move forward. Is an “HVAC engineer” the correct person to have help with the design? I am fully willing to hire someone to help with this, I’m just not sure where to look. You and some others have been very helpful here if it’s an option to discuss further and in more detail and to work out a design plan remotely, that would also be great. Please let me know what you think, thank you so much.
Hi Dennis, hoping you’ll see my reply above. Trying to contact you and Akos to discuss this more if possible. Please reach out to me at [email protected] thank you.
Bryan, yes you're looking for a Mechanical Engineer with an HVAC specialty. I'm up in Canada, and not a licensed engineer, so cannot be of much help to you in Colorado :-(
As Akos has mentioned (also a Canuck), Zehnder will be more expensive up front, however their system comes to you designed for your spec, so once you factor in an engineer's fee etc. it is likely a wash, and maybe less expensive!
I think your best bet in this case is Zehnder. They will design the system for you and provide a complete install kit with all the pipes, fittings and controls.
This isn't cheap though. The Zehnder ERV is actually not that expensive but all those bits and pieces add up.
The nice part is the ducting is small so you can fish it through existing walls and floors. The units come in a number of sized, you should be able to do a whole hose with a single unit without issues and they will handle all your bathroom exhaust as well.
Premium product but you'll get a very efficient and well performing system.
In case you do want a DIY setup, the attached Venmar manual is quite helpful. Section 3 and 7 are a really good guide to designing your own standalone ducting system for an HRV/ERV. You will likely be in good shape if you plan for 20-25 CFM per occupant. My system is heavily automated and will run at 50 CFM or not at all when no one is home, but very often is ramped to 75 or 90 CFM with all four of us here. Your home's leakage rate and outside wind levels have a significant impact on actual CO2/VOC/Radon levels in the home, but you should be just fine at that 20-25 CFM/person target.
Venmar has integrated with Broan so my old web links to this manual don't work...so, attached here for you :-)
Thoughts on an ERV layout like this?
It would involve creating one soffit across basement ceiling and one soffit across main floor ceiling, located above the bedroom doors.
Hoping this could be an 8x8 soffit or similar so that it’s not too intrusive but need to work out ducting design further.
I am trying to balance simplicity with effectiveness — is this too little or too much? Not aiming for perfect, just logical and worthwhile to do.
Photos show one system in the basement, then one system in the main floor and loft together.
(I would also need to add kitchen range exhaust vents and dryer vents separately, plus one radon vent.)
Continuing to play with ideas and make progress.
Attached file 1: Basement with basement ducting shown
Attached file 2: Main floor with all ducting shown
Attached file 3: Basement and Main floors overlaid to show how they align
I've been weighing minimal systems with minimal ducting and no or minimal soffits vs a more thorough system with supplies in each bedroom and returns in each bathroom, etc.
I keep going back to a complete system that taps into each bathroom, since I'll need to run vents from those either way and this would minimize penetrations through the exterior.
Latest idea I'm toying with is to go with a single 200 CFM (or similar) ERV that services the whole house. I'm hoping this single system will mean I only have to build a soffit across the basement (left to right in the attached images) and be able to head vertical into the main floor and loft off of this through the walls.
Any concerns for noise transfer across two separate apartments if I have a single system with ducting to each bedroom / bathroom?
Is it correct that I need about 90 CFM in the main unit and 50 CFM in the basement, or what is the best way to calculate this? Is a 200 CFM unit sufficient to would it need a higher boost ability?
Volume of main floor and loft is 22,300 cubic feet (130 cfm at .35 ACH). Volume of basement is 11,000 cubic feet (62 cfm at .35 ACH).
Is the noise of the ERV acceptable if it is located in the basement bedroom closet, adjacent to the main basement bedroom? Can it be in the open closet or should it be walled off with a door? Haven't navigated how to solve that yet.
I could do two separate systems, but it would mean another potential noise maker in the main floor primary bedroom closet, would also require 2 more penetrations through my concrete walls to the outside, and another soffit added on the main floor.