Best practices for ERV register locations and vent hoods
My ERV plan is to use a dedicated duct system to bring supply air (fresh air) into the rooms near the ceiling. This makes sense to me so cooler air can mix with conditioned air from the mini-split. I would have the return air register about a foot up from the floor. I read that most installations have both supply and returns near the top of the walls. This would make for longer duct runs. Is this recommended?
I’m ending up with more penetrations through the envelope for ERV, bath fans and dryer venting than I would like. All have built in backdraft dampers. (I don’t think the dryer does) What is recommended for a product or method to improve air sealing the outside air openings? Good vent hood products, another damper?
Zone 6B
Thanks
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I'm pondering the same sort of thing. If you go to UltimateAir's website, they actually propose the opposite of what you're suggesting; supply at the floor, exhausts at the ceiling. I'm not exactly sure why. I have no choice on the main floor of my house but to put both supplies and returns in the ceiling, as it's slab on grade and fairly open concept. On the second floor I have the added options of floor and interior walls in most rooms. Do you have your ERV yet? I heard that Zehnder gives you a free design when you request a quote. I'm still awaiting my quote, so I can't confirm that. I can't help you with the sealing of penetrations; seems like it will be a significant problem. My house has just the ERV and a few exterior electrical outlets as penetrations.
Jim,
HRVs and ERVs usually pull stale air from bathrooms -- and bathroom exhaust grilles are traditionally near the ceiling. That way the ventilation system does a better job or removing the humid air after a shower.
More information here: Installing a Heat-Recovery Ventilator.
Thanks for your help. Trevor, I do have the ERV. Panasonic FV-10VEC1.
I came up with a thought for the penetrations. The ERV and bath fans can connect to either 4" or 6" duct. I was planning on using 6" flex to the outside for less static pressure than 4". Could I reduce them to 4" where they leave the house? Does that make sense?
Thanks again
Jim,
The Panasonic FV-10VEC1 instructions allow you to use 4 inch ductwork if you want (see top image below).
The instructions also allow you to use a special fitting (a Y fitting with a split duct that is partitioned down the middle into two cross-sections, each shaped like a half moon) to reduce the number of wall penetrations. See second illustration below.
You can click on the illustrations to enlarge them. When clicking, note that there are two illustrations, so you have to click twice -- once near the top, and once near the bottom.
.
Supply: Ceilings of bedrooms, closets, living rooms.
Exhaust: Ceilings of kitchens (opposite side of the range hood), bathrooms, laundry rooms.
IMO keeping exhaust off the floor will extend filter life of the HRV/ERV and keep bends in the duct work to a minimum. I also don't think it's possible to install ducted ports in a 2x4 wall cavity.
With regards to exterior penetrations you can buy wall caps which have dampers and many range hoods have a set of dampers (flimsy) installed. Range hoods are rather simple. It's all about capture area and power. Check your codes for make up air requirements when using high power (ex, >600 cfm) range hoods because of the headache of having to create yet another wall penetration with an electric damper.
http://www.prolinerangehoods.com/1-801-973-3959/support/what-size-range-hood-do-i-need/#size
Ducted ports are possible in a 2x4 wall, but it requires specialized (and probably expensive) materials. The piping is 2.5" ID, so the flow is limited. At 20CFM, pressure loss is about 0.16"H2O over 33' of pipe. The flexibility of the semi rigid pipe means you don't need any elbows so that would help a bit. Zehnder sells the stuff, and there's at least one other make which I don't know the name of.
Here's what David Hansen wrote in his article, Installing a Heat-Recovery Ventilator:
"We use mainly 30-gauge galvanized ductwork. In 2x4 partitions, we use 6-inch oval duct, which measures 3 1/2 by 7 1/2 inches and comes in 5-foot lengths. Oval duct has a smaller airflow capacity than round but is perfectly adequate for the individual wall stacks. Each register mounts in a 6x10-inch stackhead, a duct fitting that makes the transition from a rectangular register to oval duct."