Heat Recovery Ventilators

Starting to see more Heat Recovery Ventilators (HRV’s) on energy-efficient homes. This one had a HEPA filter installed. Does anyone know anything about what’s it’s possible to safely inspect on these. Fan, filter, damper?

There are also Energy Recovery Ventilators (ERV’s) which transfer moisture in addition to heat, but I have yet to see one. Do any of you see them?

Sarted putting both types in way back in 1981!!! There’s a long thread on HRV/ERV’s at Fine Homebuilding’s web forum that I was party to about a year ago. One of the “guardian” posters suggested that it should be turned into an article for the magazine.

As I mentioned on another thread here, I drew up my own report format and I put in a section devoted to interior house ventilation including HRV’s. I have in my possession a copy of a report from probably the largest franchisor with a line that goes “An air exchanger was noted.” It’s like a drive-by inspection!!!

May get back here tomorrow; just got back from delivering and discussing a report until 11:15 PM Atlantic time and then a 45 min drive home…Are there any comparably paying “real jobs” out there?

How do you inspect them, Brian? What part of the country are you in?


I’m outside of Halifax, Nova Scotia (7,500 degree days)

As far as I know, there are 6 or 7 actual different manufacturers with a lot of branding going on for Carrier, Lennox, Bryant, and others. Some of the units are very simple and cheap “contractor” models with few operational options/adjustments and names like “Constructo” and “Tradewinds” that separate them from full featured lines. On the cheaper units, to make adjustments, you must go to the unit (in the basements up here) and flip a switch, etc or…with one I just saw a week ago (in a new “upscale” condo!!!), you actually go into the electronics box and change some DIP switches, not a homeowner friendly item. (the condo buyer was a single retired spinster not likely to make the changes herself!)

The full featured, more efficient lines have better interior electronics (more choice of fan speeds…up to 4 in some units), better defrost strategies/mechanisms, controls with more operational modes such as timed air exchange periods with “off” (wait state) periods or alternately, air recirculation/filtration periods. Some the timed air exchange periods are preset/unchangeable or can be programmable (depends on the brand).

In cold areas with outdoor temps below -2 or -3 celsius ( 25-27 F) for long periods, all units have to have a defrost strategy; as the outgoing warm air containing water vapour gets colder, condensation occurs (hence the drain hose) and as the incoming air goes below freezing, frost starts building up in the exchange core outgoing air passages. Defrost strategies have ranged from (1) pre-heating the incoming outdoor air electrically so it does not get cold enough to cause frosting (can be hard on the power bills in very cold climates) to (2) shutting off the outdoor air supply duct by means of a motorized damper and re-circulating warm house air through both sides of the exchange core until it defrosts to (3) shutting down the supply air fan and letting only warm exhaust air flow out through the core until it defrosts.

So you can see an any HRV is not the same as any other HRV. Experience or a very good connection in the field who deals or has dealt with many brands is almost necessary to do a good job on an HRV inspection. There have been some company specific problems that can easily be missed without some inside knowledge.

For example, the above mentioned lady had me inspect the new condo because I had inspected (pre-purchase) her two year old detached house for another client I found that her 2 year old HRV had no low speeds (2) functioning (also found a leak in the basement she didn’t know about). She fought me through E-mails (some a bit rude) for 2 days about going back to her house for no fee to prove that her HRV was not working properly in all settings. I made her the offer that if I missed a call- no charge with a sincere apology but if I was right, it was $100 + taxes. In the end, I was correct and she had to “eat crow” (her words) and, by the way, “Do you inspect new condos?”

The most common thing I find with HRV’s is that they are not serviced regularly or at all: many screened fresh air inlets are blocked with leaves, cobwebs and other organic debris; the filters are very dirty, especially the fresh air being full of insects (have seen both filters so dirty that the fans are spinning in a vacuum, virtually moving no air!; the condensate drain pipes have fungus/algae growing in water remaining in the loop/trap.

Again getting late here for me (drove 300 miles today, inspected 4 houses for energy retrofit purposes- 9hrs straight, no meals, breaks) going to ZZZZZZZ. will continue later


Forgot to include a couple of links to info on HRV’s

www.gov.ns.ca/energy : Search for a brochure titled “Ventilation for New Homes” (PS: I wrote about 90% of this)

http://www.nrcan-rncan.gc.ca/com/index-eng.php : Search for “Heat Recovery Ventilators” (had nothing to do with this)