Air filtration and purification for Scarborough, Durham and GTA homes
The one-inch filter in the slot beside your furnace is there to protect the blower and the coil from dust. It was never designed to clean the air in your house. Filtering the air rather than the equipment takes different hardware, matched to the system you already own. Metropolitan Heating and Air Conditioning has fitted air quality equipment to forced-air systems across Scarborough, Durham Region and the GTA since 1979.
Call (416) 283-5698, Monday to Friday 8:00 AM to 4:00 PM.
MERV, particle size and what the number actually means
MERV — Minimum Efficiency Reporting Value — rates how much of a given particle size a filter captures on a single pass, and runs from 1 to 16 on residential equipment.
A MERV 6 fibreglass panel catches lint and the coarse dust that would land on the blower wheel, and little else. MERV 8 starts capturing a meaningful share of the 3 to 10 micron range — the band that includes most household dust and pollen. MERV 11 to 13 reaches into the 1 to 3 micron range, where fine dust, smoke particles and cooking aerosols live. Above 13 you are into commercial and clean-room duty.
Single-pass efficiency is only half the picture. What leaves the house is efficiency multiplied by how many times the air passes through — which is set by how long your blower actually runs. A MERV 13 filter on a system whose fan runs eight minutes an hour does less work than a MERV 11 on a system running a continuous low-speed fan.
Why a higher MERV is not automatically better
Every filter resists the air passing through it, and that resistance is measured as pressure drop. Push a high-MERV filter into the one-inch slot a furnace was designed around and you raise static pressure across the blower. Airflow falls. In heating that raises the temperature rise across the heat exchanger; in cooling it drops the coil temperature and can freeze it.
The fix is surface area, not a weaker filter. A four- or five-inch media cabinet holds a deeply pleated filter with many times the face area of a one-inch panel, so it delivers MERV 11 to 13 at a pressure drop the blower can live with — and it lasts six months to a year instead of one to three months. Fitting one means cutting the return plenum and adding a cabinet, which is why it is a job rather than a purchase.
Media, electronic and whole-home HEPA
Media cabinets are the common answer: no power, no moving parts, a replaceable pleated cartridge, and performance that does not fall off as the filter loads.
Electronic air cleaners charge particles as they pass and collect them on plates. Pressure drop is low and there is nothing to buy each year, but the plates must be washed on a schedule or performance drops away, and some designs produce a small amount of ozone.
Whole-home HEPA units capture 99.97% of particles at 0.3 microns. Their resistance is far too high to sit in the main air stream, so they are plumbed as a bypass: a dedicated fan pulls a slipstream off the return, filters it, and returns it upstream. That gets HEPA-grade filtration on part of the airflow without strangling the furnace, and it needs its own power and duct connections.
UV lamps and where they belong
A cooling coil is wet for months of the year, and wet surfaces in the dark accumulate biological film that fouls the fins and blocks the drain pan. A UV lamp mounted to shine on the coil face is used to keep that surface growth down, which keeps the coil clean and the condensate draining. Judge it as coil and drain-pan hygiene equipment. It filters nothing — it does not capture particles, and it is not a substitute for filtration.
Fitting it to the system you have
What we look at first: the blower type and its available static pressure, the size and condition of the return ductwork, how much plenum length there is to work with, how the fan is controlled and how many hours a day it runs, and the state of the coil and drain pan. Equipment is wired into the furnace control so it cycles with the blower. Filtration sits alongside humidity control — different problems, and neither substitutes for the other.
Book an assessment
Call (416) 283-5698 weekdays 8:00 AM to 4:00 PM, or tell us what you are trying to solve. See all indoor air quality services and whole-home HVAC. Licensed and insured, in Scarborough since 1979.