Pacific ventilation in Victoria

Mr. Panton, glad you have given the topic more than cursory consideration, since residential kitchen ventilation can affect many aspects impacting the home and its occupants. Of course, the construction codes are minimum requirements, and as you have pointed out those minimum requirements are not the same everywhere. Here are some things to consider when selecting a residential kitchen exhaust makeup air system: Air flow rate (cfm) exhausted equals air flow rate replacement - No matter the rate of air (small or large) being exhausted via a kitchen range hood that same amount of air will be replaced in some manner - some combination of cross-envelope infiltration, designed make up air provision, backdrafting, or other means. - A corollary to this is the rate of air which can be exhausted is limited by the rate at which it can be replaced. For example, if the home has the ability to replace only 200 CFM of air, then you can only exhaust as much as 200 CFM, even if the exhaust system is designed to provide more. This can be an issue in tightly constructed homes. - Sure, we all know this, but it’s important to keep this in mind while considering what's going on in the dwelling as a whole while a range hood exhaust system is operated. Air flows as a result of pressure differential - When a range hood exhaust system operates, the blower creates a pressure differential between the hood entrance and the building exterior. Air flows as a result of the pressure differential, and is limited by the resistance associated with duct length and fittings, building tightness, availability of replacement air, etc. - Of course, this same principle applies to makeup air. Air flows into the home only as a result of a pressure differential. o A home with no kitchen ventilation make up air provision relies upon infiltration through the “leakiness” in the dwelling envelope. That infiltration occurs as the exhaust system blower removes air from the dwelling causing the dwelling’s pressure to become negative with respect to outdoors. The tightness or leakiness of the dwelling envelope along with the exhaust system’s blower performance capacity result in the magnitude of depressurization and rate of infiltration. o A home with a passive kitchen ventilation makeup air provision still relies upon the exhaust system’s blower creating a depressurization, such that makeup air is drawn in through the passive opening. Therefore the passive provision needs to include an opening large enough as well as duct length and fittings of a size to allow for the flow of makeup air adequate to replace that being exhausted at a depressurization level minimal enough to not cause appliance backdrafting or other issues. o A powered kitchen ventilation makeup air provision does not rely upon dwelling depressurization. Rather, the makeup air system’s blower creates the necessary differential pressure for outdoor air to flow through the makeup air opening and the ducted system and be supplied into the dwelling at a rate that matches the exhaust rate. When such a combination of exhaust and powered make up air are balanced, these systems operate together while not imparting any pressure impact on the dwelling’s interior. Construction codes - those which you’ve referenced - The Florida construction codes would appear to be most concerned with occupant safety (the potential for backdrafting), but we hope those codes would also consider other aspects such as health and comfort. And, it would appear that the construction codes are making some assumptions, which we all know don't apply to every residential dwelling: o Assumption: All homes are leaky enough such that 400 CFM of exhaust can be replaced via infiltration without endangering the occupants due to backdrafting gravity-vented appliances. We know that as little as 3 Pa (0.01” w.c.) depressurization can result in backdrafting of gravity-vented appliances. Many range hood exhaust systems include blowers capable of producing more than 250 Pa (1.0” w.c.) differential pressure when operating. o Assumption: All homes are leaky enough such that 800 CFM of exhaust can be replaced via infiltration without endangering the occupants due to backdrafting of power vented or direct vented appliances, and those homes will never be retrofitted with a gravity-vented appliance. We know that power-vented and direct-vented appliances can be backdrafted at depressurization levels far less than that which can be produced by kitchen exhaust system blowers. - You might consider the dwellings which you design: Are they of tight construction? Are those dwellings leaky enough such that makeup air will take the path of leakiness in the envelope rather than via appliance and fireplace vent systems? Perhaps infiltration can't be counted upon even though the local codes would allow for it. - There are other reasons why it is undesirable to have a depressurized interior space. Of course, any amount of depressurization will induce the migration of air and its contents into the home, including sources from the air surrounding the dwelling, the air in the attic space, and the air in the soil or spaces beneath. These sources can impact comfort and health, as we know. Other considerations for passive makeup air for residential kitchen ventilation - A passive or non-powered kitchen ventilation makeup air system requires at least some amount of interior depressurization. For such a system, some amount of infiltration and its negative effects will occur. - Any duct work transporting air as part of a passive makeup air system will need to be sized to accommodate the rate of flow at extremely low static pressure resistance, resulting in unusually large duct sizes for the contained rate of flow. This can limit where the passive makeup air entrance is located as well as where and how the passive makeup air is supplied to the dwelling. - It's not practical to apply filtration to the passive flow of makeup air, since doing so would likely result in too much resistance for the small level of depressurization available for the creation of flow. Other considerations for powered makeup air for residential kitchen ventilation - A balanced, powered kitchen ventilation makeup air system creates no depressurization or pressurization on the interior space. - A powered kitchen ventilation makeup air system allows for reasonably sized ductwork for the transportation of the air from outdoors into the dwelling. Additionally, since a blower is employed to create the flow of makeup air, more flexibility might exist as to where the exterior entrance and interior supply of makeup air are located. - Powered kitchen ventilation makeup air can be filtered, since these system’s blower works to overcome the pressure loss associated with that filtration. - There is of course some amount of additional cost to be expected with the installation of such a system. Chances are you already know much of this, and perhaps you weren't looking for such a lengthy reply. But, we at Fantech have spent a tremendous amount of time thinking through the dynamics of ventilation and the impacts it has on a building and its occupants. We feel it's important to share what we know and help spread the understanding of such topics within our industry. Fantech’s solutions might not always be what you need, but perhaps for the homes with which your design expertise has been entrusted by your clients, our makeup air solution might very well make the most sense. Thank you very much for paying some of your attention to this topic. We hope some of this has been helpful.

@@Fantechusa Thanks for the thorough response. On our commercial projects our engineers already satisfy this, but I could never understand why such an important topic is ignored in residential; and I've asked this for many years. Even the code I referenced is VERY relaxed. One question, though: provided that plumbing or gravity vent appliances are out of the equation, what negative effects are there living in a depressurised environment? Are oxygen levels lower since it is a vacuum?

@@Troy-Moses It’s probably obvious that the most imminent danger related to building depressurization is the potential it creates for the back-drafting of appliances and fireplaces. We aren't aware of any adverse direct physiological effects of the relatively slight depressurization caused by uncompensated air exhaust. Such depressurization is likely no greater than what a person might experience on a regular, commercial airline flight. Also, the availability of oxygenated air for the building’s occupants shouldn't be affected by a slight interior depressurization, assuming there is a separate and adequate provision for the dwelling’s continuous ventilation requirement. However, there are additional undesirable effects that can occur when a building is even slightly depressurized. When a building is depressurized, we lose some control over what enters the building and how it does so. It's not practical that even the most tightly constructed homes are completely airtight. Depressurization will induce infiltration of air and all its contents, and that infiltration will occur anywhere there are seams or gaps in the building envelope. Where the building has ground contact or crawl spaces, humidity and radon can be drawn in with infiltration. Infiltration can occur through exterior walls, too. Outdoor air is often uncomfortable and it can contain pollen, spores and dust. As this outdoor air travels through a building's exterior walls, it brings along humidity and the potential for fungal growth. When this inherently unmanaged infiltration reaches the interior, comfort and indoor air quality can be tainted. So, back-drafting potential aside, depressurization in a dwelling should be considered undesirable. Balanced ventilation solutions exist for kitchen range hood ventilation (compensating makeup air systems) and whole dwelling continuous ventilation (ERVs and HRVs, aka fresh air appliances), so that design professionals can employ these systems to provide ventilation in homes without inducing depressurization.

@@Fantechusa Solid response, thank you.