Indoor air quality is a phrase that gets used loosely, and two products get bundled together under it that solve genuinely different problems. A HEPA filter and an energy recovery ventilator are both sensible upgrades in the right house, but one of them cleans the air you already have and the other one brings in air you do not have. Work out which problem you have before you spend anything.
What a HEPA filter actually does
A filter sits in the return path of your system, on the way from the house back to the air handler. A standard filter catches the larger debris: dust from the return vent, pet hair, lint. A HEPA filter, which stands for high efficiency particulate air, is a much finer media that traps small particles as well.
A true HEPA filter is rated to capture 99.97 percent of particles at 0.3 microns. That size matters because 0.3 microns is roughly the size at which particles are most easily breathed deep into the lungs. Smoke, fine dust, pollen fragments and other airborne contaminants are all in that range. In a house with allergy or asthma sufferers, that is the whole point of the upgrade.
There is a cost. A HEPA filter puts more restriction on the airflow, so the fan works a little harder and the system uses slightly more electricity. A HEPA is a health purchase, not a money-saving one. What it does give you is air that is genuinely cleaner at the register, provided the system is sized correctly and the filter cabinet has the space for it.
If you are not sure which problem you have, there is a simple way to narrow it down. Put your hand at a supply register and feel the air. If it is cool and the house still smells musty or feels close, you need ventilation. If the air is fine and the problem is dust and allergy symptoms, you need better filtration.
What an ERV actually does
An energy recovery ventilator is a ventilation product. It brings outdoor air into the house through its own duct, and it pushes indoor air out through a second duct, usually near the kitchen or bathrooms where moisture and cooking odours are highest.
The recovery part is the clever bit. As stale, warm or cool indoor air leaves, the outgoing stream passes next to the incoming outdoor air, and heat or coolness transfers between the two. The fresh air arrives in the house closer to the indoor temperature, so you are not paying to condition air that has just come in from outside. ERVs also move moisture, which is why they come in an ERV version and an HRV version. The ERV suits a climate where the outdoor air is dry, which is exactly what Stockton and the Central Valley get for most of the year.
None of that happens with a filter. A HEPA filter never adds a single cubic foot of fresh air to your house. If the air in your home feels stale and close, more filtration will not fix it.
HEPA filters vs ERVs side by side
| Feature | HEPA filter | ERV |
|---|---|---|
| Main job | Traps fine particles from the air moving through the system | Brings outdoor air in and removes indoor air |
| Adds fresh air | No | Yes |
| Best for | Allergies, asthma, dust, smoke and wildfire particles | Tight homes with stale air, and humidity control |
| Where it goes | In the filter cabinet of the existing system | Two dedicated duct runs, one in and one out |
| Ongoing upkeep | Replace the filter on a schedule, and the upstream filter too | Clean the core and change its filter |
| Effect on your bills | A small increase, because the airflow is restricted | Recovers heat or coolness from the outgoing air instead of losing it |
| What it will not do | Ventilate the house | Trap fine particles on its own |
What to ask before you buy an indoor air quality upgrade
- Ask whether your equipment and filter cabinet can physically take the filter or the ERV, rather than assuming they can
- Ask what the system is losing in airflow, and how the return air will be rebalanced if a filter is added
- Ask where the ERV air would enter and leave the house, and whether there is a sensible path for those ducts
- Ask how often the filter or core has to be replaced or cleaned, and what that costs you in parts and time
- Ask what the total installed price is, in writing, before the work starts
Two things will make a bigger difference than any single piece of equipment. The first is a clean filter and clean coils, because a restricted airflow system cannot deliver clean air to the rooms. The second is sealed and insulated ductwork, because leaking ducts waste conditioned air before it reaches anyone. We handle both, and they are the first three jobs on our ten step maintenance checklist.
When to stop and call a licensed technician
There are points where a filtration project stops being a weekend job.
- Stop if your system is not holding temperature, because adding restriction to a system that is already starved will make it worse, not better
- Stop if you are tempted to seal or cut ductwork yourself to make room for a unit. Leaky or crushed ducts cost you money every month of the year
- Stop if you are thinking of installing a filter cabinet that needs an electrical supply or a new return plenum
- Stop if anyone in the house has asthma or a serious allergy and the plan is to wait and see. That is a conversation to have with a technician, not a job to experiment with
Call (209) 351-6000 and tell us what you are trying to fix. We will look at the system, tell you honestly which of the two upgrades actually applies to your house, and quote it in writing before any work starts.
