Whether you are suffering from asthma and allergies or simply want better air quality in your home, you may have come across whole house air purifier systems when searching for an air purifying solution online. When compared to portable room air purifiers, on first glance whole house air purifiers may seem like the perfect solution. After all, these systems will be able to cover the entire home as its name suggested, right? Unfortunately the term “whole house air purifier” is a misnomer, as many systems sold promise much more than they can deliver.
If you’re interested in purchasing a whole house air purifier system in lieu of multiple portable air purifier units, let’s take a look at how whole house systems work and why they may not be able to clean the air in your entire home.
How do whole house air purifiers work?
As mentioned above, “whole house air purifier system” is a catch-all term used by an unregulated industry, which can sometimes confuse consumers — many assume it’s an advanced equipment that can be installed into your existing residential HVAC system to clean and purify all the air in your home.
Whole house air purifying systems can be broken down into these main different types of systems:
- Filter-based units that are installed in HVAC furnace systems and air intake points
- Duct-based units that are installed into air duct path, before or after the air handler in a central HVAC unit
- Stand-alone systems installed into closets or attics, followed by installing additional air intake and exhaust into the home
Because all of these units generally may need an HVAC tech to install, there is a lack of transparency in regards to the system’s cost and effectiveness. As it stands, if you simply search online for “whole house air purifier” systems you’ll often find HVAC repair and servicing vendors pitching these systems as a worthwhile investment.
But what these vendors often don’t clarify are the types of system they are selling and what comparable options there are on the market. For filter-based units, vendors may be charging you a premium for simply opening your HVAC unit and swapping out a filter medium.
For more involved systems such as the duct-based systems, these are often extremely cost prohibitive (and labor-intensive) – giving consumers sticker shock as vendors and HVAC service companies often don’t make the total cost clear on their website and literature, further confusing consumers.
With this guide, you’ll have a better idea of what each type of whole house air purifier system entails, how they work and what their potential negatives may be.
Working in conjunction with your residential HVAC unit
Before we discuss the different types of whole house air purifier systems listed above, you should be familiar with how most modern HVAC units work in a home. Although HVAC stands for heating, ventilation, and air conditioning – most residential systems in the United States only entail heating and cooling – thereby placing the burden of ventilating on exhaust fans and windows (for natural ventilation). This means exactly what you think: if you’re running your home’s heating or cooling system – the system isn’t necessarily introducing fresh air into your home. In fact, most outside air comes into homes by infiltration from the cracks and openings in windows and doors, even when they are closed.
Most homes in the United States utilize either a heat pump system or a split setup of forced air heating system along with a central air cooling system (using the same ductwork within the home), a whole house air purifier system that works in conjunction with this type of HVAC system will be affected by an HVAC system’s limitations, which we will discuss further along below.
Diagram 1: Typical residential HVAC system and its ductwork.
Replacement filter based “whole house” air purifiers
In essence, replacement filter-based “whole house” air purifiers are simply furnace filters for your HVAC unit. These are sold as either a media filter or a more expensive electronic air cleaner to be installed into your HVAC unit in lieu of the media filter. Sometimes, replacement filters for return air path are also combined with furnace filters as an air purifier solution. You’ll often find these replacement air filters sold in bulk quantity at home improvement stores as they are meant to be changed frequently.
- Replacement air filters for return air grills: thin 1-inch filters sold in packs.
- Replacement filters for furnace/system: thick 5-inch filters, usually sold individually.
While some of these filters are marketed as air purifiers, their main purpose is first and foremost keeping dust and debris from your HVAC system, allowing the system to run efficiently – and not as an air purifying solution for your home.
Diagram 2: Locations of replacement filters in return path of a residential HVAC system
Negatives of replacement based filters for HVAC as an air purifier solution:
- Requires your HVAC unit to be constantly running. In order for the air in your home to actually flow through the filter media and have potential pollutants go through the filtration process, you’ll need to actually run your HVAC system constantly with the blower fan of the system on. This can be excessively wasteful in energy when compared to a portable unit.
- Limited by the design of a home’s HVAC system. Replacement based filters that are sold as an air purifier solution are hindered by the limits of an HVAC unit to circulate and ventilate air through your home. As we’ve established above, most residential systems are forced-air based and their primary function is to cool and heat your home by forcing air through ductwork into each individual room, NOT to purify the air in the room.
- Limited locations where air is pulled into system. Air being pulled into a forced-air based HVAC system comes from the return air grill, which for most homes is either in the hallway ceiling or hallway wall and not in each individual bedroom. Because most modern homes are limited to only 2~3 return air grills, these replacement air filters can only filter limited locations within a home, as larger particles such as animal dander can settle quickly and will not be able to travel the distance to the filter media, even with the pressure difference from the supply air forcing airflow to the return air intake.
- Difficult to maintain. Furnace based filters are not easily accessible for many homes and are hard to replace frequently, potentially causing build-up of bacteria and mold within the filter medium, further spreading them when the forced-air system pushes contaminated air through your home
Duct-based whole house air purifiers
Duct-based whole house air purifiers are a significantly more expensive solution when compared to replacement filter based whole house air purifiers. These solutions essentially replace a section of your ductwork, generally in the return air path area before the air reaches the HVAC air handler unit and in place of the ductwork are installed filters. Filtration is done at this level within the ductwork and some of the more expensive variations utilize HEPA filters. For systems that utilize HEPA filters, the blower of the existing HVAC system cannot take care of the additional pressure drop and has to be replaced with a more powerful blower.
Because these systems are still relying on filtration as their main air purifying method, you will still need to replace these duct-based air filters on a regular basis. Adding to the difficulty, because of their location (generally within crawl space of a home), these filters are much more difficult to replace vs. replacement filter systems mentioned above. Examples of such systems include the IQAir Perfect 16 or the PureAir systems. These systems cost thousands and will require professional installation.
Given their professional installation requirement, many of these duct-based systems are unsurprisingly sold through HVAC servicing vendors – adding a layer of conflict of interest and lack of transparency in your options. Most vendors will simply carry one type of unit and not offer or mention other available solutions – even if they may be more cost effective for your home.
You’ll find duct-based systems usually installed in three different configurations:
- Bypass config in the return air path of a ductwork. The filter medium is installed in one of the return air ductwork, leaving the other as a “bypass” to not impede airflow of your HVAC system. (Yes, this means the other return path won’t be filtering any pollutants based on this system configuration).See diagram 3 below for reference.
- Non-bypass config in the return air path of a ductwork. These whole-house HEPA air purifier systems are installed at the main point of where return air ductwork is located, just before the air enters the heating and cooling system of your home. Because HEPA can restrict airflow to an HVAC unit (reducing the effectiveness of their primary function of cooling and heating), these type of non-bypass systems often come with their own blowers to further induce air to your HVAC unit.
- Non-bypass config in the supply air path of a ductwork. Instead of being installed in the return air path (of where air is being pulled into a system), these type of whole-house air purifier systems are installed in the air supply path of the ductwork (where air is being pushed out of a system). See diagram 4 below for reference.
Diagram 3: Bypass config of a duct-based air purifier system
Diagram 4: Supply air config of a duct-based air purifier system
Negatives of a duct-based whole house air purifier system:
- Limited to homes with a forced air HVAC system. Because these are duct-based systems, they are of course limited only to homes with a forced air HVAC system. If you don’t have forced-air heating or central air cooling, you will not be able to use these systems.
- Inefficient as it requires HVAC unit to be constantly running. Like replacement filters above, because these are installed into your ductwork, they simply aren’t filtering unless your system is actually running. If you’re the type to not frequently run your cooling or heating system because your house is well insulated and energy efficient – then you will still need to continue running your system fan for filtration to actually happen.
- Bypass config still lets in unfiltered air. Many duct-based systems are installed in a bypass configuration into your HVAC unit (see diagram 3 above). They are installed this way in order to not impede airflow to your cooling and heating system, but because there will be unfiltered portions in a bypass configuration, this negates the point of a whole house air purifier system since partial, unfiltered air is still being taken to your HVAC system to be distributed to the rest of your home.
- Mold and algae can grow in the duct. With high enough humidity levels, mold and algae can grow within a duct-base system. These filter based systems cannot take care of the pollutants being generated in the part of the duct that comes after the filter.
- Limited to your home’s HVAC design. Like replacement based whole house air purifiers, duct-based systems are limited to your HVAC ductwork and how many return air grills you have in your home, and where they are located. This limits the area where the air is actually being purified.
- Does not work well with multiple zone systems. Modern homes with two and three zone ductwork systems may not work well with these duct-based whole house air purifier system unless you install separate whole house system for each zone which would become prohibitively expensive.
Whole house air purifier system vs portable room air purifier units
As you can see with the many pitfalls above, a whole house air purifier system relies heavily on your home’s HVAC system. But the reality of the situation is that your home’s HVAC system and ductwork are designed to efficiently cool and heat the air in your home, not to clean the air in your home or introduce outside fresh air.
Beyond the points listed above for each type of whole house air purifier system, you should also consider the negative aspects of a whole house air purifier system when compared to a portable air purifier unit.
Negatives of whole house vs. portable units
- Mismatched design purpose. HVAC systems are designed to cool and heat a home, and limited return air paths are to ensure proper airflow and pressure. Because of this a whole house air purifier system is only going to be able to take in air and pick up pollutants in one area of the house where the return air grill is located (generally in hallways and not in bedrooms). In comparison, you can take your portable unit from room-to-room, cleaning the air of the space you utilize the most.
- Can be ineffective. Duct-based whole house air purifier system are ineffective in bypass configuration as they will still partially let in unfiltered air. A portable system is designed to clean all the air in its designated volume.
- Inconsistent performance between homes. The performance of a whole house air purifier system isn’t consistent as each home and its HVAC system (along with the ductwork) is unique, whereas portable units are designed to clean a specific square footage.
- Energy inefficient. May not be energy efficient when you compared a whole house air purifier system to a portable unit. As the whole house system is married to the HVAC, you will need to constantly run your HVAC fan (or cooling and heating system) to actually filter the air.
- Expensive. Whole house air purifier systems can be incredibly cost prohibitive, especially when you factor in the labor cost from an HVAC servicing vendor. Ductwork systems are especially expensive while only pulling in air from select locations in the home and may end up costing more money vs. buying individual portable units for each room of your home.
- Lack of transparency and confusing options. If it’s a replacement filter based system, what will fit with your HVAC system? Or return path grill? If it’s duct-based, where should you install for proper airflow and actual filtration? What about modern homes with zoned cooling/heating? Compared to portable units, you will need to make many decisions shrouded behind sales pitches and hidden prices.
Whole house air purifier systems sound good on paper, but not in actual practice
For many people, the initial concept of a “whole house” air purifier system can sound appealing. After all, these systems are labeled as “whole house” units – even though realistically they are only filtering in air from select locations of a home. Because of how many whole house systems are sold, information about these air purifier solutions is often lacking in transparency, especially when sold through HVAC technicians and service vendors.
HVAC systems in a residence are designed to heat and cool your home and their primary function is simply not to purify the air in your home. The filter elements for an HVAC system are meant to protect the system first, and filter pollutants as a distant second. At the end of the day, portable units offer the flexibility and choices that whole house based systems won’t be able to match, both in cost-effectiveness and actual air purifying efficiency.
