You're asking about adding Makeup Air (MUA) to a range hood, specifically one with a 700 CFM capacity. This is a very important question, as properly addressing MUA is crucial for safety and performance, especially at higher CFM levels. Here's a breakdown of how MUA systems work with range hoods and what you need to consider

Why Makeup Air is Important (Especially at 700 CFM):
Combustion Safety

When a powerful range hood (like a 700 CFM unit) exhausts a large volume of air from your home, it creates negative pressure. This negative pressure can draw exhaust gases from fuel-burning appliances (furnaces, water heaters, fireplaces) back into your home. This is a serious health hazard.

Appliance Performance

Negative pressure can also impact the efficiency of your furnace, water heater, and other appliances, causing them to work harder and less effectively.

Drafts and Comfort

Negative pressure can also cause drafts, especially around windows and doors, making your home uncomfortable.

Building Codes

Many building codes now mandate MUA for range hoods above a certain CFM threshold (often 400 CFM or lower), precisely because of the safety concerns. Check your local building codes!

How Makeup Air Systems Work with Range Hoods

There are several approaches to providing makeup air. The best option for you will depend on your climate, the size and layout of your home, and your budget. Here are the most common types:1.

Passive Makeup Air



Description

These are the simplest and least expensive options. They consist of a gravity-dampered vent (or multiple vents) that allows outside air to enter the house when the range hood is operating. When the range hood is off, the damper closes to prevent drafts.

Installation

A vent is typically installed in a wall or ceiling, often near the range hood. It connects to an outside vent.

Operation

As the range hood pulls air out, the negative pressure created overcomes the damper's resistance, and outside air flows in.

Pros

Low cost, simple installation, no electricity required.

Cons



Limited Control

The amount of makeup air is solely dependent on the pressure difference created by the range hood. It may not provide enough air to fully compensate for the exhaust.

Unconditioned Air

It brings in cold (or hot) outside air directly, which can cause drafts and affect your home's heating or cooling.

Filtration

Often lacks filtration, so you're bringing unfiltered air into your home.

Wind Sensitivity

Can be significantly affected by wind. A strong wind could force the damper open even when the range hood isn't running, or hinder the airflow when it is.

Suitability

Rarely adequate for 700 CFM. Best for very mild climates and lower CFM range hoods, and only if allowed by code. Even then, careful calculation and testing are needed.2.

Active (Powered) Makeup Air with a Dedicated Fan



Description

This is the most effective and recommended solution for higher CFM range hoods. A dedicated fan brings in outside air whenever the range hood is on. This fan is often interlocked with the range hood's fan, so it turns on and off automatically.

Installation

A separate duct run from the outside to the inside of the house is required. The makeup air fan is installed in this duct. Electrical wiring is needed to power the fan and to connect it to the range hood for synchronized operation.

Operation

When the range hood is turned on, the MUA fan also turns on, supplying a calculated amount of outside air. The amount of air supplied is typically based on the range hood's CFM setting.

Pros



Precise Control

Provides a controlled and consistent amount of makeup air.

Can be Conditioned

Allows for heating, cooling, and filtering of the makeup air.

Reliable

Less affected by wind or other external factors.

Cons



Higher Cost

Significant upfront investment in equipment and installation.

More Complex Installation

Requires ductwork, electrical connections, and often professional installation.

Noise

The fan adds to the overall noise level.

Suitability

Ideal for 700 CFM and essential in colder climates, where you need to heat the makeup air.3.

Active Makeup Air Integrated with HVAC System



Description

This integrates the MUA system with your existing furnace or air handler. When the range hood is on, the HVAC system is activated to bring in outside air.

Installation

Requires a professional HVAC technician to modify your existing system. Ductwork and control wiring are needed.

Operation

The HVAC system draws in outside air through its existing intake and distributes it throughout the house.

Pros



Conditioned Air

The makeup air is heated or cooled by your HVAC system.

Even Distribution

The air is distributed throughout the house.

Cons



Complex Installation

Requires significant modifications to your HVAC system.

Capacity Limits

Your HVAC system must be sized appropriately to handle the additional load.

Potential for Imbalance

If not properly designed, it can create imbalances in your home's heating and cooling.

Suitability

Can be a good option if your HVAC system is already oversized and you want conditioned makeup air. However, it's crucial to have a qualified HVAC professional assess your system's capabilities.

Important Considerations for Installation



Sizing

The MUA system must be sized to match the CFM of your range hood. It's best to slightly overestimate to ensure adequate makeup air. The range hood company or a professional HVAC technician can help with this.

Interlocking

The MUA fan (if used) must be interlocked with the range hood so that it turns on and off automatically. This can be done with a simple relay or a more sophisticated control system.

Filtration

Adding a filter to the MUA system is highly recommended to prevent dust, pollen, and other pollutants from entering your home.

Heating/Cooling

In colder climates, you may need to heat the makeup air to prevent drafts and maintain comfort. This can be done with a dedicated electric heater or by integrating the MUA system with your HVAC system. In hot, humid climates, cooling the makeup air can also be beneficial.

Location

The location of the MUA intake is crucial. It should be located away from sources of pollution, such as dryer vents, car exhaust, and garbage cans.

Backdraft Dampers

Use backdraft dampers to prevent outside air from entering the home when the MUA system is not operating.

Local Codes

Consult your local building codes to ensure that your MUA system meets all requirements. This is crucial!

Answering Your Specific Questions



"Are these systems fan forced or just some sort of dampered opening to outdoor air?" As explained above, they can be either. A simple damper system is often insufficient for 700 CFM, especially in climates with temperature extremes. A fan-forced (active) system is generally recommended for higher CFM range hoods. "How the makeup air system gets installed." The installation will vary depending on the type of system you choose. Passive systems are relatively simple to install, while active systems require more extensive ductwork and electrical connections.

Recommendation

Given that you're looking at a 700 CFM range hood,

I strongly recommend a powered/active makeup air system with a dedicated fan. This will provide the most reliable and effective solution, and it will also allow you to heat or cool the makeup air if needed. Consult with a qualified HVAC technician to design and install the system. They can assess your home's needs, determine the appropriate size of the MUA fan, and ensure that the system meets all local building codes.

In summary, don't skip the makeup air system. It's essential for safety, comfort, and the proper performance of your appliances, especially at 700 CFM. Flag for review