Practical ventilation for older home
Greetings GBA,
I live in a 1966 home in Toronto, Canada.
I just had my 28 year old furnace & a/c replaced with an all electric heat pump system and loving the new system which is much quieter than the old.
My next HVAC challenge is to improve ventilation in the home. In occupied rooms, the Co2 is hitting 1000 during the day, and the bedrooms hit 1500-1700 at night. The air smells stale. Both my wife and I work from home so I’m concerned about our air quality.
I started exploring an ERV with my hvac contractor which they would tie into the new air handler, but they were unable to find an acceptable solution for the vents on the exterior due to my basement being significantly below grade. The intake and exhaust would end up being only about 3 inches off the ground which they said could be problematic in the winter with snow. I shovel the snow though, so I’m not sure how much of a real problem this would be. My dryer vent is 3″ off the ground too and I haven’t had an issue with it.
My other concern is: will my heating system be able to keep up with an ERV attached?
I’m wondering if I should try and proceed with an ERV tied to my air handler despite the above, or if there are better ways to get fresh air into an older home without running a ton of new dedicated ducts?
Thanks!
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Did you see this recent article: https://www.greenbuildingadvisor.com/article/integrating-an-erv-or-hrv-into-a-forced-air-system? The links in the sidebar are also worth reading; similar questions to yours come up here regularly.
Dryer vents close to grade aren't a problem because they vent hot air which melts snow. An intake 3" above grade in a snowy location will get clogged; even if you're usually diligent about snow removal, there will be storms where the intake gets covered up. I'm not sure if that puts undue stress on the ventilation motor but it might.
Have you considered point-source ventilation, such as Lunos E2 units? They are effective and efficient, if somewhat expensive.
Thanks Michael. Good article. The main takeaway seems to be that that the ERV should be linked to the AHU in a way that the AHU blower runs when the ERV runs. This does not sound complicated (My AHU has G terminals) but knowing the hvac contractors around here, I'll have to make sure they don't mess it up!
Something that I can't do is connect the bathroom exhaust to the ERV since the Bathroom is on the 2nd floor and my AHU is in the basement. I'll have to pull stale air from elsewhere. Is it possible to pull it from upstream on the return drop and then add the fresh air closer to the AHU? I'm attaching an image of my new system.
A friend mentioned the Lunos too, which is a neat idea, but I believe I would need several of them to bring fresh air to all the bedrooms which would really add up. Leveraging my existing hvac ducts seems to make more sense to me and the article you linked appears to agree with that.
>"I'm not sure if that puts undue stress on the ventilation motor but it might."
For centrifugal blowers, you never want to restrict flow on the intake, but you can restrict flow on the outlet. For axial fans (think of box fans, things like that), you don't want to restrict the intake either, since it causes the fan to overspeed.
I would think you could come out of the basement, then 90 up and go a little ways up to keep clear of the snow.
Bill
Thanks Bill,
I think the 90 elbow could work. I'm surprised the contractor didn't think of this. Any downsides to this? Also can a 4" duct work or must it be 6"?
90s give some flow restriction, but otherwise shouldn't be a problem. Regarding 4" or 6" duct, check the documentation for the ERV you want to install. Some units will need the larger duct, others may only specify the larger duct for runs over some length (longer runs may need larger duct to deal with flow restriction).
Bill
4" ductwork can work with a smaller unit but you have to double check the losses. You'll probably be running at around 60 to 70CFM, two elbows are about 60' equivalent length, so at 70CFM that adds about 0.2" of friction loss. Most ERVs can do 0.4" so it can be made to work but you have to be careful with the rest of the ducting.
Another option is to pop up from the basement inside the back of a closet on an exterior wall to go outside. A small bulkhead can hide the ducting on the inside and it would be much cleaner on the outside. Something like one of these wall boxes would let you put the two ports pretty close:
https://reversomatic.com/product/intake-exhaust-wall-boxes-dvs-100/
Don't use a 4" intake/exhaust. It will be somewhat restrictive, even at 75-90 CFM, particularly if your ERV has 6" ducts. If you use a larger ERV (assuming adjustable speed ECM motors here) and run it a slower speed, efficiency will be higher.
I'm in the process of removing the 4" exterior hoods I installed for a smaller Panasonic spot ERV and replacing with 6".
With regard to the topic of an elbow and vertical run outside for more ground clearance, climate zone is a big issue. In cold climates, for intake, this is likely fine. On exhaust, there will be cooling of relatively moist air on very cold days and it will freeze for sure at the elbow, eventually blocking the vertical run upwards. This is why it's not done.
I have a similar challenge to you with respect to an older home (as in 120 years old) and a setup that makes ERV/HRV integration very difficult to the existing forced air ducting. Our system dumps all the fresh air in our main floor living area, and picks up stale air from the basement stair well...so just one supply and return in the home. I run the ECM motor on the furnace in circulate mode at night to move the fresh air on the main floor to the bedrooms which works ok. This also means that 16 hours of the day my furnace fan is not running, just the HRV setup which only uses about 40 watts of power. This setup is not ideal, but based on the AQ sensors in all three floors, it works. The automation setup takes CO2 (averaged across three sensors), Radon (basement), and VOC ( 2nd floor, where it peaks on mornings with girls and hairspray!) to set the ventilation rate. Averaging CO2 on the three floors makes sure that 2nd floor CO2 peak levels at night (bedroom's are all on the 2nd floor) are accounted for by the system.
Thanks Dennis and Akos these were very helpful comments!
Sounds like I need to stick with 6" ducts and get them coming out of the outside wall at the correct height.
I will look around for the bulkhead option. The twin vent unit is very interesting. I imagine this would be arranged according to the prevailing wind direction? It may be possible to pop up into a kitchen cabinet (not ideal but may be the lesser of the worst options). My challenge is the other exahusts in the area - basement bathroom and dryer. How far should the ERV vents be from those? They are not used very often, if this matters.
I need to find a good hvac contractor who can set things up properly or maybe I should just hire a handyman with all the tools and instruct him exactly what to do!
Attaching pic of the side of my house where this is all happening. I marked the potential ERV intake/exhaust locations which would require bulkheads in the kitchen in a location where a future cabinet is planned to go.
My mental picture of a 1966 home is something so leaky that the curtains flap when the wind blows. Usually no supplemental ventilation is necessary, what's needed is more sealing. Have you had a lot of sealing done? Are you sure that meter is accurate?
I haven't renovated my office, in an upstairs bedroom of my 1830 house. It's about as drafty as livable spaces get. Yet my Awair meter shows CO2 going over 1,000 ppm in the afternoon if the window isn't open.
Ha, yeah I think that may be typical and I know what you're imagining. In my case, this house has had previous work done to it to improve the air sealing. The blower door test came back at ACH 4 @ 50 and the auditor said that this was borderline in need of mechanical ventilation. Based on my CO2 readings I would agree. Measured with 2 devices: aranet4 and airthings wave plus.