HRVs, Part 3 of 3: Installation Defects

For the last two entries I've blogged about HRVs. In part one, I covered what HRVs are for and how they operate. For part two, I covered HRV maintenance and operation. Today I'll discuss installation defects.
The most common defect I find with HRVs is that they were never balanced. When HRVs are installed, a technician needs to balance the system to make sure the air getting exhausted is equal to the air coming in. If more air comes in than what goes out, you'll have a pressurized house... and vice versa. Neither of these conditions are good for the home.


To make sure an HRV is balanced, I look for a balancing sticker and I check to make sure that the balancing damper controls have been screwed in place. If they're not screwed in place, a balancing sticker means nothing. If I don't see a balancing sticker, I don't make a big deal about it, but I'll often make a note in my report that it's missing. If there are no balancing screws, I recommend having the HRV professionally balanced.


Most HRVs are installed hanging from straps or chains and springs to minimize the transfer of any annoying vibration from the fans. If an HRV gets mounted to the wall, I check the installation manual to make sure that this is an acceptable installation, and I listen on the other side of the wall to see how loud it is. When they're mounted incorrectly, they can be very noisy!

As a rule of thumb, the intake and exhaust locations at the exterior of the home should be located at least six feet away from each other. I've never seen an installation manual that allowed anything less. It's also important to make sure the intake is at least ten feet away from any sidewall vented gas appliances, such as a powervent water heater or furnace. The intake should also be located at least ten feet away from anything smelly, such as where the garbage containers get kept.


The ductwork that feeds the intake from the exterior and exhaust to the exterior needs to be properly insulated. If it's not properly insulated, you'll feel an obvious cold draft.


If the HRV ducts are only attached to the furnace's return air, they must be at least three feet away from each other, and the furnace's blower fan must turn on with the HRV to prevent the air getting added to the house from short-circuiting and getting pulled back out of the house. Every manufacturer recommends connecting the furnace's blower fan to the HRV for optimal performance, but it's not always a requirement.

Every HRV needs to be plugged in to an outlet. If the HRV is running off an extension cord, this is an improper, unacceptable installation. Repair requires the installation of an outlet.


That's about all of the HRV installation defects that I can think of, and that concludes this mini-series on HRVs. As always, please email or post any comments or questions!

Reuben Saltzman, Structure Tech Home Inspections - Email - Minnesota Home Inspections

HRVs, Part 2 of 3: Maintenance & Operation

Last time I blogged about why houses need HRVs.  This time I'll write about maintenance and operation of HRVs, and I'll try to cover the stuff you should know if you own one.  The information in this blog is general - every manufacturer will have their own set of instructions and their own maintenance schedule.

Maintenance

• Every three to six months the filters should be cleaned by vacuuming to remove as much dust as possible, then washed with warm water and mild soap.  Some filters can also be washed in the top tray of a dishwasher, but this may tarnish the aluminum finish.  The filter below should have been cleaned a long, long time ago, and this is what I find at almost every home inspection - way more than dirty furnace filters!

• Every three to six months Clean the condensation tray with damp cloth.  The condensation tray is the area where water will collect in the bottom. The condensate drain should be checked, and replaced if needed.  The drain tube usually consists of clear plastic tubing with a little loop that creates a trap to prevent odors from the floor drain or wherever else from getting sucked in to the HRV.

• Every three to six months Check the intake grill at the exterior of the home to make sure it's clean.  These get very dirty, as there is a fan constantly pulling air in.

• Every six to twelve months the core should be cleaned by removing it and letting it soak in a mixture of lukewarm water and mild soap.  Rinse the core thoroughly when done.  If you own a summer core, don't get it wet, as you'll cause permanent damage to it.  Summer cores can be cleaned by vacuuming with a brush attachment.

• Every one to three years the fans should be cleaned.  This typically requires removal of the fan assembly.  Check the owner's manual for specific instructions, or hire a professional to do this.

Operation

Operating an HRV is usually quite simple.  If the HRV has a switch located on the unit itself, it will typically have a couple of the following settings, but not all:  On, High, Low, Off, or Remote.  If your HRV has a "Remote" setting, you'll probably want to use that one. This will allow the HRV remote controller, usually mounted on the wall next to the thermostat,  to turn the HRV on and off.  This remote will also typically have a dehumidistat, which controls how much moisture is in the air.

If the bathrooms in the house have funny little wall buttons instead of bathroom exhaust fan switches, it typically means that the HRV system has had ductwork installed in the bathrooms.  This is an acceptable alternative to bathroom exhaust fans.  When the wall button is pushed, this will turn on the HRV for somewhere between 15 - 60 minutes, or will kick the HRV in to high gear for 15 - 60 minutes.

Every HRV should also have a defrost cycle, and the HRV should go in to the defrost cycle automatically when it gets too cold.  The defrost cycle is actually quite simple; the exhaust fan just runs for about five minutes, which forces a bunch of warm indoor air through the core without bringing in any cold air.

If you plan to operate your HRV during the summer, check your owner's manual to see what the manufacturer has to say about it.  If your HRV is designed to run during the summer, you'll probably need to remove the standard winter core and install a summer core.  The difference is that the summer core is designed to remove moisture from the air coming IN to the house, rather than the air leaving.  If there is no mention in your owners manual about running your HRV during the summer, you probably shouldn't.

That's about all for maintenance - for any more specific instructions, you'll need to check your owner's manual.  Next time I'll talk about installation defects.

Reuben Saltzman, Structure Tech Home Inspections - Email - Minneapolis Home Inspections

HRVs, Part 1 of 3: Why Houses Need Them & What They Do

Many months ago I wrote a blog about how houses can often havemoisture problems when old furnaces are replaced with high efficiency furnaces. The fix that I mentioned at the end of the blog was to install a Heat Recovery Ventilator, or HRV.  The character in that blog finally got around to installing an HRV in his house, and solved all his moisture problems! For the first time since he installed his high efficiency furnace, he no longer has condensation on his windows during the winter, and he couldn't be happier about it.

Today I'll share some basic information about how HRVs operate and why they're needed in today's newer, tighter houses.

New Houses Don't Breathe As most people know, new houses are constructed much tighter than they used to be - they don't leak air all over the place.  I've heard a lot of old-school home inspectors and building contractors complain about this, and you probably have too.  The rant goes something like this: "We build houses so damn tight that they don't breathe, and they end up rotting from the inside out!  Things were a lot better when we didn't have all these stupid house wraps."

These cranky doom sayers are only partially right - yes, we build houses tighter today, but we've also figured out how to prevent mold and moisture problems, and how to improve indoor air quality.  This is where HRVs come in.

HRVs Provide Fresh Air An HRV works by constantly bringing fresh air in to a house and exhausting stale air.    The air that gets brought in to the house gets passed through a screen at the exterior, then through a filter inside the unit, then through the HRV core, which is actually a heat exchanger.  The heat exchanger allows the fresh outdoor air to get warmed by stale indoor air right before the indoor air gets exhausted to the exterior.  This allows about 60 - 80% of the heat in the air to be re-captured.  The diagram below illustrates this principal.

To understand how an HRV works, interlock your fingers together and picture warm air flowing through fingers in one hand, and cold air flowing through the fingers in the other hand.

HRVs Remove Moisture Besides providing fresh air, HRVs also remove a lot of moisture from the air.  Old, drafty houses get dry in the winter because they're leaky, and the moist indoor air is always getting replaced with dry outdoor air.  Not so with newer houses - they stay humid during the winter, and HRVs are often needed just to get rid of all the excess humidity.  As the warm, moist air passes by the cold air, the moisture will condense.  This is why HRVs have a drain running out the bottom.

 

HRVs Lower Radon Levels Because HRVs constantly change out the air in a house, an HRV will reduce radon levels when working properly.  During a recent Eden Prairie home inspection that I also performed aradon test at, I had the HRV running during the majority of the radon test, but I tripped the GFCI outlet for the last hour of the radon test during my inspection.  Look at the jump in radon levels at the house from NOT having the HRV running!  Any time a radon test is performed, if there is an HRV present at the house, it should be up and running throughout the duration of the radon test.

HRVs Have Many Names If you hear any of these terms, someone is probably talking about an HRV:

• Air-to-air heat exchanger
• Air exchanger
• Whole house ventilator
• Big square thingy in the furnace room
• VanEE system (brand name)
• ERV

The last one, ERV, stands for Energy Recovery Ventilator.  These are similar to HRVs, but ERVs are pretty rare here in Minnesota - I think I've seen two of them, ever.  They're designed for more humid, southern climates.

If you don't have an HRV at your house and you think you need one, you could always just turn on an exhaust fan and leave it running.  This will be very inefficient, but it will change out the air in your house.  I call this the Poor Man's HRV.

Next week I'll talk about the maintenance needs of HRVs, and the week after that I'll discuss installation defects.

Reuben Saltzman, Structure Tech Home Inspections - Email - Eden Prairie Home Inspections