DIY Low-Budget ERV/HRV Installation
karlb_zone6a
| Posted in General Questions on
In the comments section of his “Three Ways to Ventilate a Home” article, Allison Bailes suggests that a DIY install of an ERV can be had for ~$2000 for a small(ish) house.
Anyone care to outline how to do this? We can assume we’re talking about a budget-friendly ERV, and not a Zehnder (e.g., the Panasonic Intelli-Balance seems to be well-regarded here, and hits the $1000 mark that Allison suggests)
Metal duct and pipe aren’t that expensive, but prefab manifolds and plenums sure are! Is the solution just a very simple layout, and to DIY the manifolds?
Thanks
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Replies
I don't think you need a manifold or a plenum if you are only ventilating and not heating just a simple trunk and branch layout using rigid duct for the trunk and flex lines for the branches.
Good call, Alex! My application will actually be a retrofit, but a simple trunk and branch layout makes good sense in new builds, and might also be doable for me, as the (conditioned) attic and (air-sealed) basement are 100% available for runs.
I’m hoping to do the same. Very little diy friendly info on ducting out there, but I see it as very low risk if your erv is self balancing and leaks or incorrect sizes in conditioned space likely not a big deal. Martin linked an article about erv installs before that was helpful. I’m planning on mostly using semi rigid flexible ducts.
Thanks for the reminder, Carson.
For reference, Martin's article is linked below (there may be others):
https://www.greenbuildingadvisor.com/article/ducting-hrvs-and-ervs
I'm doing exactly this right now. Panasonic ERV and DIY ducting with rigid Ys instead of plenums and some flex duct mixed with more 4" rigid. The vents are adjustable in each room so I'll be able to balance a bit that way. I'm sure the Zehnder engineers are spitting their coffee on the screen reading that, but at 1/10th the cost it's the only way I can go on this build. I'm sure their system would be more efficient and perfectly balanced but I just can't afford it.
It's a 1500 sf space and the ERV is centrally located so some of the runs are only a few feet long. The rough in has been inspected and passed. I won't be installing the ERV unit for a while though.
Good call with the rigid Y duct, Andy. We're maybe 1700 sf, on two levels, so many of the runs will also only be a few feet.
I've read of someone using Zehnder's manifold and ComfoTube flex, paired with a different brand's ERV, which is also a somewhat tempting strategy.. Setting aside the cost premium for the Zehnder ERV itself, their extras add up quickly!
I really wanted to use the Zehnder system. Like, really, really wanted to but no matter how I tried to simplify or adjust the plan it just never got anywhere close to affordable.
Their ducting setup was quoted somewhere around $3000 - $3500 while I doubt I spent more than $300 on rigid pipe and flex duct.
I'm sure the Zehnder system would work better, look nicer (behind the drywall), and be easier to install, but I just couldn't justify the 10x premium with the budget being as stretched as it is. To be fair, if I was building this for someone else and had to charge labor and be responsible for future service and performance, then yeah...Zehnder would make a lot more sense.
I think if you're doing it yourself if means you're trying to save money. Using the Panasonic as the reference for such an install means 50 cfm for each input and exhaust motor fans. That's not much. You need to work as efficientIy as you can, especially on the fresh air outlets.
It's best to have the fresh air going to the bedrooms only. This is especially true if you close the doors at night. As was said it's a good idea to use 'y'' branches because they are much more aerodynamically efficient that a plenum with right angle branch ducts coming out of it.
If you have fresh air inputs to rooms that can have their doors closed it means you need to have a way to evacuate stale air from those rooms. However, you shouldn't put the return air supplies in the bedrooms because then you would short circuit fresh air circulation getting to the rest of the house. Instead there needs to be a jump duct from each bedroom getting fresh air to other rooms of the house that get the return ducts. A jump duct can be as simple as cut out in the wall between two rooms with registers on each side. Those rooms might be a bathroom, kitchen, or living room. It's important to always create as much distance with in a room between a jump duct and a return or supply duct so that the air circulates throughout the room and doesn't short circuit most of the room space.
It's a fact that the lower the fan power the more important it is to lower aerodynamic drag to get proper air circulation. It's the same reason as I used 'y' s instead of plenums.
A big jump duct is also a big sound transfer opportunity. Not sure I'd want that in the bedrooms.
A 1” door undercut will allow about 60 cfm according to This piece on Allison’s site: https://www.energyvanguard.com/blog/can-door-undercuts-work-as-return-air-pathways/
I can see why that’s not enough for heating or cooling, but I can’t see why it wouldn’t work for the volumes we are talking about for a realistic HRV/ERV installation.
Well, my standard method when DIYing is to think things out for myself and use conventional wisdom as just a guideline. For the most part that has kept me on the straight and narrow and has had kept me successful. When in doubt be conservative and don't trust conventional wisdom.
For instance, if you have 3 bedrooms and 1 bathroom and exactly equal distribution paths from each bedroom to the one bathroom there would be only 33 cfm differential air exchange for each bedroom. I wouldn't want to depend on an undercut door for such a small CFM. And that would be if the Panasonic is turned on full blast. I'd rather just make it easy for such a small ERV and cut a separate large jump duct. That's just me. I'm conservative about engineering and generally don't trust contractors to tell me what is in my best interest to know.
I installed a Venmar ERV myself in our last house. The unit has dampners on the top of the unit to balance the unit. I read up on how to balance these then bought an inexpensive magnehelic gauge and probe. I placed the unit itself in a heating utility room in the garage then ran 6" duct work through our one story house. Fresh air intake and stale air to outside went right out behind the unit. I concealed the duct runs in decorative soffits, then built coffered ceilings, trimmed them out with crown molding and things worked out pretty well,
I too ran fresh air to the bedrooms and had my returns in the bathrooms as my bathroom vents. I installed a switch on the wall that would put the units into "boost" mode 10, 20, or 30 minutes to add extra CFM to get rid of moisture from showers. This was just low voltage thermostat wire that hooked into the bottom of the ERV. I installed the central control unit in a hallway near the masterbedroom.
I bought a handheld anemometers to check my flow at the exhaust and intake ports, to try to get the rooms about the same amount of air flow based on size.
I was real happy with the Venmar unit, the filters were hand washable a couple times, and had no maintenance issues. All and all anyone with a building background who is willing to do a little research can install a balanced ERV unit in a small house.
It sounds to me like you did an excellent job and that the Venmar is a good unit. Congratulations!
Agreed with Eric! If this weren't your LAST house, I'd encourage you to take some more photos, and write up your install :)
We have since moved from the house I did the ERV install on, otherwise I'd be happy to share some pics.
Great job. The new Venmar models (and therefore broan and vanee) are self balancing so it's even easier to DIY now.
To those of you that have done it, do you have a good source on tutorials for installing ducting for an erv? Did you get past inspection (new build)?
I don't have any tutorials and can't recall finding any good overview on duct installation, but I just applied basic physics and common sense to the process. Keep the runs short, seal the ducts so they don't leak, avoid any sharp bends, plan the paths.
My rough in passed inspection no problem.
great to hear Andy.
You could also consider getting a few TwinFresh (or similar) HRVs and putting them in certain rooms. Pretty simple to install, and pretty cheap. I've had one in a semi-detached garage (converted to home office) for 3 years and haven't had a single problem. Brought my CO2 levels down from 1200-1500 to about 700-800.
Aun, how many sqft are you servicing on the Twin Fresh? Building a garage+ADU and thinking that I will go with a TF HRV in ADU (600sqft) and also wire it so it turns on when the stove vent is on. I know the bedroom is the best place, but I think the open living/kitchen area is better spot.
286 sq ft. I think I leave mine on the "medium" fan speed but it's been so long since I messed with it that I don't remember for sure.
600 sq ft is probably pretty big for a TwinFresh, but you could check their data and CFM numbers and confirm whether you think it would work. It might be OK on the high fan setting. The other good thing about Twinfresh is that they are pretty easy to install, so if you start out with 1 unit, and your CO2 levels aren't quite where you want them, you could add a second. I think with certain models you can even have them communicate with each other so that they work in tandem so that you never get a negative or positive pressure in your space.
One complaint about them is that, as soon as I had purchased my unit from them, they started completely ignoring me. I had an install question and another minor question or two, and never received any response. (Whereas, before they had my money, they were pretty quick to respond.) But for the price and my specific application, TwinFresh was by far the most attractive option to me. I would buy another one in the future.