How to be sure HRV system is up to par
QUESTION: I am moving into a new home and have ordered an HRV system. You had stated in a previous newspaper article many technicians are not knowledgeable in installing these systems. What should I look for when I do the new-home inspection? Thank you, WM
ANSWER: Your question is timely as I recently inspected two newly built homes by the same builder with different HRV installations, one correct and one not. I will offer some guidance on what to look for on the unit in your home.
I am assuming the new-home inspection you’re talking about is the walkthrough with the builder’s representa- tive prior to occupancy. This is not a true inspection since you’re only asked to identify any issues you know about. You’re not likely educated in what to look for, other than cosmetic or obvious defects. Ideally, you could have had a CAHPI inspector accompany you on a full inspection prior to this point, but that was not likely done.
The problem with your inspection is not only the limitation on your knowledge, but the limited time given to you by the builder’s representative and the need to identify items without prior access. However, I do commend you on seeking advice on this issue so you are better prepared for your inspection.
As for evaluation of your HRV, I will try to provide a crash course on what to look for on your walk-through.
Firstly, you should ensure the ducting connected to the HRV unit is going to the right locations. While this may seem rather complicated, it can be simplified considerably by looking for markings or stickers on the HRV unit itself. There will either be a schematic drawing, showing which ducts should be connected to various areas, or labels directly beside the ducts where they connect to the box.
There should be two solid metal ducts connected to the stale air coming from the house and the fresh air to the house connections. The fresh-air duct should be connected to the return-air ducting on the furnace and the stale air to ducting coming from the bathrooms and other areas of the house.
The next two connections should be to insulated ducting, which terminates at hoods outside the house. One will be for the fresh-air intake and the other will be for exhaust air. These vent hoods should be easily visible on the exterior of the house walls or foundation and often have screens or grates integral to prevent pest intrusion. If these ducts appear to be in the correct location, which is not normally a problem in most installations, you can move on to the next step.
The next item to check is the control device for the HRV. This is normally located in a hallway or part of the main living area in the home and usually beside the thermostat for the HVAC systems. There are several different styles of controls, but most have a manual portion of the control and a humidistatic portion.
The HRV can also be manually activated with switches in the bathrooms. This aspect replaces the older-style exhaust fans and can be activated much the same way as in older homes. Again, these are most often working fine in most new-home installations.
The main problem seems to be with the humidistatic controls. HRVs are designed to control excessive humidity in homes by exhausting stale, moist house air and replacing it with dry, fresh outside air. This not only removes pollutants from the living space caused by cooking, heating and other human factors, but also eliminates a lot of the moisture produced from these activities.
This can be done manually by turning the HRV on continuously, using the main control or bathroom switches, but may keep the unit running too long, or not long enough. The humidistat on the main control should be adjustable to engage the HRV only when the relative humidity (RH) in the home surpasses a certain level. That level can also be adjusted to accommodate changes in weather and climatic conditions. If that part of the control is not functional, then the HRV is only a more energyefficient version of an exhaust fan and not being used to its maximum potential.
To check if it is working, the HRV should come on automatically when the RH settings are turned down below the normal range without engaging any other switches or controls. It should also shut off when the humidistat is further adjusted above the RH in the home and both levels are normally noted by a small click when the control is rotated beyond that threshold.
The final item to check is whether the HRV controls are cross-connected with the furnace fan. This is important to provide maximum ventilation, especially in some of today’s larger homes. The fans integral with the HRV are quite small, and the furnace fan can be of major assistance to provide effective air circulation when it is used in combination with the HRV.
This can be checked simply by listening to the furnace while the HRV is manually engaged. There may be different settings on the controls to turn this function on or off, so be careful not to jump to conclusions if it doesn’t work when first attempted.
In the last few years, I’ve seen many HRV units improperly installed or not functioning properly. Lately, most of the problems have been non-functioning humidistatic controls, but other items may also be a concern. As with any appliance, HRVs require regular maintenance, which includes cleaning filters and the core as per manufacturer’s instructions.