Tag Archives: alaska

Building workshops & classes this spring

While it might seem like summer is far away, the building season is right around the corner, and now is a good time to finalize any plans for upcoming home improvements. If you’re interested in reducing your home’s energy use, there are several opportunities this spring to learn about energy efficient building and retrofit techniques.

The building addition at CCHRC, which opened last year, features passive solar design, radiant floors, a pellet boiler and a super-insulated building envelope. There are efficient technologies in the original building as well, including a masonry heater, ground source heat pump, a sewage treatment plant, solar photovoltaic panels and thermal storage. Tours are offered at 2 p.m. on the second Thursday of every month and feature both the original building and the addition, and include plenty of time for questions and discussion, as well. Spring 2014 tours will take place Feb. 13, March 13, April 10 and May 8. In addition, the Builders Resource Library at CCHRC contains information on many aspects of cold climate construction and heating systems. The library is open Monday-Friday, and a catalogue is available online atcatalog.library.uaf.edu (select CCHRC from the Library menu).

Golden Valley Electric Association offers one-on-one instruction through its Home$ense audit program. Through the $40 program, an energy auditor visits your home to discuss ways to reduce your electrical usage and energy costs. To sign up, call the member services department at GVEA at 458-4555 or visit www.gvea.com.

Classes on more advanced topics are offered by the Alaska Craftsman Home Program (ACHP). Advanced Cold Climate Construction will be held Feb. 12 and 13 in Fairbanks, covering the latest energy efficient construction methods on topics such as insulation, vapor retarders, windows and ventilation. The class includes a construction manual and certificate for continuing education credits. Also, ACHP will

offer a one-day class on the Building Energy Efficiency Standard (BEES) on March 19 and May 22. This class covers the BEES requirements for insulation values, air leakage, moisture protection and ventilation. Fees and registration for these classes and more information can be found at www.achpalaska.com.

For those interested in wood heating, UAF is hosting the Firewood Workshop from 10 a.m. to 2 p.m. Saturday in the Bunnell Building. The workshop covers how-to tips for cutting and drying wood, operating a wood stove and more.

Finally, the annual Interior Alaska Building Association Home Show will take place March 28-30 at the Carlson Center and will feature topics including financing, remodels and new construction. There also will be seminars and demonstrations on a variety of topics related to homebuilding. The home show kicks off the summer building season in Fairbanks and is an excellent way to gather lots of information about energy efficiency.

What are pellets made of and how to shop for them?

Pellets are a biomass fuel that is used in pellet stoves and boilers. Unlike the cordwood burned by woodstoves, pellets are a manufactured fuel source that consists of biomass byproducts such as sawdust, wood chips, waste paper and agricultural waste. Pellet ingredients are bound together by pressure and heat instead of glue, as in a manufacturing plant, then sold in 40-pound bags at local hardware stores or by the ton from a manufacturer.

There are several places in Fairbanks to purchase pellets by the bag. Two types of pellets are manufactured in Oregon by West Oregon Wood Products and are made predominantly from Douglas Fir, a tree found in the Pacific Northwest. The other type is made locally at Superior Pellet Fuels in North Pole, consisting of approximately 90 percent spruce gathered from local businesses, including Windstorm Salvage Timber Sales and Northland Wood Sawmills. The remaining 10 percent consists of cottonwood and aspen sawdust and scraps from timber harvests in the Interior.

All pellets are refined by manufacturers to be uniform in size, density, moisture and energy content. However, pellets made by different manufacturers will have different characteristics because of the variety in raw materials and manufacturing processes. For consumers to compare the basic characteristics of pellets from different sources, the Pellet Fuels Institute (www.pelletheat.org) has developed standards for pellet fuels sold in the United States. Manufacturers send their pellets to a third-party lab for testing and pellets are classified into three categories, depending on the standards that the pellets consistently meet.

PFI Utility Pellets

• bulk density of 38-46 lbs. per cubic foot

• ash content 6 percent or below

• moisture content

10 percent or below

PFI Standard Pellets

• bulk density of 38-46 lbs. per cubic foot

• ash content 2 percent or below

• moisture content

10 percent or below

PFI Premium Pellets

• bulk density of 40-46 lbs. per cubic foot

• ash content 1 percent or below

• moisture content

8 percent or below

Both types of pellets available in Fairbanks exceed the PFI Premium Standard. The West Oregon Wood Products lists the specifications for its pellets on its website (www.wowpellets.com/fuel-pellets/wood-fuel-pellets/91-fuel-pellet-specs). They have a density of around 42 pounds per cubic foot, an ash content of 0.3 percent and a moisture content of 6 percent. Superior Pellets also made a testing report available for this article — they send sample pellets from the manufacturing plant each week to Twin Ports Testing in Wisconsin to ensure they continually meet Premium standards. Superior’s pellets have a bulk density of approximately 44 pounds per cubic foot, moisture content of 6.5 percent, and 0.5 percent ash content.

When purchasing pellets, homeowners should consider bags that meet PFI Premium standards as these pellets have a higher Btu content because of their low moisture and higher density. For pellets not labeled as meeting the standard, consumers should research the moisture content, bulk density and ash content when deciding which brand to purchase.

How to prevent mold growth in your home

Mold requires moisture, above-freezing temperatures, oxygen, and nutrients to grow. The nutrients can come from many building materials such as the paper facing on drywall or wood. Mold spores enter a home through open windows and doors, on the clothing and shoes of people, or in the fur of a pet. As mold spores are assumed to be present in most environments, they easily can enter a home. If spores land on a surface with available nutrients and moisture, they can grow into a colony.

Preventing mold growth usually is focused on controlling moisture, since above-freezing temperatures and oxygen also are required by the house’s human occupants. In homes, water leaks and condensation are the primary sources of moisture that lead to most mold growth. Examples of water leaks would be a break in the building envelope, such as a hole in the roof that allows rain to enter, or a plumbing leak. Condensation occurs when humid air encounters a cool surface, such as the windows in an exterior wall. When air containing water vapor cools to the dew point, it can no longer hold as much moisture and that excess moisture is then deposited on the adjacent cool surface in the form of water droplets. Air with high humidity is common in bathrooms and kitchens because cooking and showering expose the surrounding air to substantial amounts of water. However, plants, aquariums and even breathing contribute to the humidity level in a home.

Preventing mold growth

Keeping indoor humidity levels low is a big step towards preventing mold growth. Although indoor humidity that ranges between 40 and 60 percent at room temperature is best for human health, the reality is that in an extreme cold climate with temperatures below -20°F (such as Fairbanks), levels of more than 30 percent can lead to condensation forming on cooler surfaces such as windows, exterior walls behind furniture, and in closets. Indoor humidity levels between 20 and 30 percent are much safer in terms reducing the condensation risk during winters in Fairbanks, especially during very cold periods. However, this will vary depending on the insulation level of your home. Humidity levels lower than 30 percent can be tolerated by humans, however a greater percentage of occupants may experience the physical discomforts associated with drier air. To measure the humidity level in your home, you can buy a hygrometer at a hardware store or online for between $20 and $60. To prevent humidity from reaching damaging levels and maintain healthy indoor air quality, tight houses will require ventilation systems, such as exhaust fans in bathrooms and kitchens or a whole-house Heat Recovery Ventilator (HRV).

Even homes with a low overall humidity may have damp microclimates where mold can grow. Inspect areas such as crawlspaces periodically. A crawl space can produce large quantities of water vapor if damp soils aren’t covered with an intact and well sealed vapor retarder. In the crawlspace be on the lookout for water leaks, air leaks in ducts, or condensation on pipes, concrete or discolorations on wood surfaces — particularly around the rim joist area. Be sure to address any issues promptly. If there is standing water as a result of a leak, you have 24-48 hours to dry the area before mold spores can settle in and grow, so clean up the water as soon as you can, and then use a dehumidifier or fan to help dry out the area.

Damp areas on walls can be eliminated by making sure there is air an air space and good circulation between the wall and any furniture, clothing, or other objects. Firewood drying indoors also can contribute to moisture loads. A plugged or disconnected dryer vent can introduce large amounts of water vapor into the air and go unnoticed. Inspect all vents to the exterior periodically to ensure they are in good working order. Eliminate any standing water in the home. You can prevent standing water in showers and sinks by keeping drains clear and clean. Keeping a pot or kettle full of water going on the stove should be avoided.

Finally, if you do discover mold growth, it is important to clean it up as soon as possible to stop the mold from spreading and to prevent further occupant exposure.

Tips for Storing Wood Pellets

Pellet stoves are similar to wood stoves, except they burn manufactured pellets instead of cordwood. Pellet stoves typically use electricity because they are partially automated: An auger moves pellets from a hopper to a combustion chamber, an exhaust fan vents combustion gases and draws in fresh air, and a circulating fan forces air through a heat exchanger and into a room. The stoves also can be controlled by a thermostat.

Pellets are about a half-inch long and are made from compacted sawdust, wood chips and waste paper (they resemble rabbit feed). They can be made from biomass fuels other than wood, including nutshells, corn kernels, agricultural crop waste, sunflowers and soybeans. They are bound together by pressure and heat (no glue is used). Pellets are sold in 40-pound bags at local hardware stores, or you can buy them by the ton from a manufacturer.

Many homeowners store pellets near the appliance because the hopper needs to be filled occasionally by either the homeowner or through a separate automated system. For small appliances only used occasionally, you may only need a few bags on hand, but bigger or more frequently used appliances will need a greater pellet supply. Below are a few guidelines to follow for storing pellets:

1. Ideally, pellets should be stored near the pellet-burning appliance for convenience. The pellet storage location must be accessible for re-stocking as well. If you have pellets delivered, call the manufacturer to make sure a delivery truck can access the site.

2. Pellets must be kept dry so they don’t crumble, ideally stored in an area with a roof and walls. If stored on the ground, they can absorb moisture from wet soil.

3. Since they will be burned in an appliance, they should be kept as clean as possible — protected from dust and other contaminants. On that note, delivery trucks that blow pellets into a storage area can cause lots of dust, so the room should be sealed off from the interior of a home.

4. In Alaska, pellet delivery trucks typically use a direct auger system to transfer pellets into a storage system. If you order pellets from a manufacturer, ask how they will be transferred to the storage area and protect any fixtures, lights or pipes that could be damaged. Make sure the storage area can support the weight of the pellets.

5. Finally, the storage area should have ventilation and a carbon monoxide (CO) detector near the door, as pellets can release CO when stored. Another option to alleviate CO concerns is to store pellets in a silo (inaccessible to people entering it) outside of the occupied building, with an auger feed system into the pellet appliance hopper and a CO detector near the

hopper.

This last point is important because CO is a clear, odorless, and tasteless gas that prevents red blood cells from carrying oxygen. It is extremely dangerous because people cannot detect it. Typically, CO is associated with burning fuel in a combustion appliance, such as wood, pellet, oil or natural gas furnaces and boilers. CO can enter a home if a combustion appliance backdrafts, releasing combustion gases into a home instead of up the chimney.

Stored pellets can release CO, according to recent studies, though the amount depends on several factors, such as the age, content and exposed area of the pellets. This is especially a concern for enclosed storage areas that contain large quantities of pellets and are accessible to humans, such as for district heating systems or on cargo ships.

Not all pellets release measurable amounts of CO. Preliminary testing at CCHRC found no detectable CO emissions when the pellets were stored in a 30°F storeroom. Although when we sampled a plastic bag filled with pellets, sitting inside an 85°F room, the CO concentration in the bag was 60 parts per million (70ppm would trigger CO alarm if sustained for 1 hour). While the room may not have reached the same level as the bag (as the gas would have more space to diffuse), this shows the pellets have the potential to produce CO.

Be sure to take the proper precautions for a pellet storage area by ensuring the area is vented, installing a CO detector near the storage area, and being aware of the symptoms of CO poisoning. All homes with any kind of combustion appliance should have a CO detector in the living area to ensure combustion gases are not entering the home.

How can I prevent window condensation in the winter?

Windows can be a barometer for how much humidity is inside the home.

On really cold days, you may notice condensation forming on the inside of your windows. This can be caused by one or a combination of factors: excess humidity, inadequate ventilation, or poor windows. To understand and correct a particular issue in your home, you need to know some basic properties of moisture.

Condensation occurs when water vapor (a gas) turns into water droplets as it comes into contact with a cold surface. The point at which this happens (called the “dew point”) depends on the temperature and humidity of the inside air. The warmer the indoor air, the more water vapor it can “hold,” and moisture can better remain in the vapor state. When air moves next to a cold window, the temperature drops and it can’t “hold” as much vapor. That’s when you start to see condensation forming.

For example, if the indoor temperature is 70 degrees and the outdoor temperature is 0, then moisture will begin to condense on a single-pane window when there is roughly 15 percent relative humidity in the house. A double-pane window will cause condensation at around 25-40 percent relative humidity, and a triple-pane window at between 30-50 percent. These are rough numbers are based on average window insulation values.

The recommended indoor humidity levels for occupant health and comfort range from 30-50 percent. The general rule in a cold climate, however, is to target the lower end of this spectrum due to the risk of condensation within walls and ceilings. If your house has adequate mechanical ventilation, humidity is less of a concern. In Fairbanks, it’s tough to maintain anything close to 50 percent humidity in a properly ventilated house, because the winter air is so cold and dry. Because of its low moisture content, the inherent dryness of Fairbanks winter air is good for homes but not always the occupants, since the dryness can cause discomfort.

What can I do about it?

Three things: make sure your home is properly ventilated, aim for less than 40 percent relative humidity to keep both you and your home healthy, and consider replacing your windows or adding moveable window insulation during cold months.

If you already use mechanical ventilation and have low interior humidity, but are still having problems, you may need to examine your ventilation setting. If you have a heat recovery ventilator (HRV), it may be recirculating too often, which can contribute to increased moisture build up in the air. Recirculation mode closes the connection to the outside and brings exhaust air back into the rooms. Recirculation mode keeps the HRV core defrosted and saves energy, but sometimes it can run too long. Some experimentation with the HRV settings may be necessary. For example, in 20/40 mode the HRV brings in fresh air for 20 minutes and then recirculates for 40 minutes, and likewise for 30/30. If you’re getting condensation in your current mode, try decreasing the amount of time the unit recirculates.

Also make sure air is allowed to circulate—either passively or mechanically—throughout the entire house. If you close the door to the bedroom, the air can become cold and moist enough to condense on windows.

Older, poorer performing windows can create problems no matter what you do to your interior air. Bad seals around operable windows, metal spacers between the panes, and inadequate insulating value can cause the window surface to get cold enough for condensation to occur. If you’re not ready to invest in new windows, consider some type of moveable window insulation like foam board (on the outside) or well-sealed plastic film (on the inside). A CCHRC guide to different types of window insulation can be found at

http://www.cchrc.org/evaluating-window-insulation.

UAF Sustainable Village Cuts Energy Use in Half

The Birch House at the UAF Sustainable Village used the equivalent of 367 gallons of heating oil in the first year of occupancy, less than half as much as an average home its size in Fairbanks.

The Sustainable Village homes at the University of Alaska Fairbanks are a new model of energy efficient, affordable housing for Interior Alaska. The four 1,600-square-foot homes were built at the university in 2012 to demonstrate that super-efficient, climate-appropriate houses could be built without breaking the bank. University students helped design and build the homes, adding their own ideas about sustainable campus living.

The homes incorporate experimental techniques, like solar hydronic heating and adjustable foundations on permafrost, that should reduce energy costs and improve the durability of the homes. CCHRC, along with student residents, have been monitoring the energy use and indoor air quality at the homes for the past year.

On average, the homes used less than half as much energy as an average new house in Fairbanks. The lowest user was the Willow house, going through the equivalent of 366 gallons of heating oil No. 1, or 48.3 million Btu, for both heating and domestic hot water from September 2012 to September 2013. The average same-size house in Fairbanks uses about 920 gallons, according to the Alaska Housing Finance Corporation’s database. Even the average new energy efficient house uses about 660 gallons per year. That’s more than the biggest energy user at the Village, the Spruce House, which used only 463 gallons of oil equivalent.

How do the homes save energy?

The homes are super-insulated and incorporate energy-saving features like heat recovery ventilation, triple pane windows and Energy Star appliances. The Willow House has a REMOTE wall with 8 inches of exterior foam insulation and 3.5 inches of fiberglass batts inside the wall cavity (for a total of R-51). That’s more than twice the insulation value of a conventional 2×6 wall with 5.5 inches of fiberglass insulation. Space heating and hot water are provided by a propane boiler and three solar thermal collectors.

The Spruce House, on the other hand, has a double wall filled with 18 inches of cellulose insulation (R-64), and a forced air heating system with a small diesel heater that heats fresh ventilation air.

Because each house has roughly the same heating load, the difference in energy use can be largely explained by the differing mechanical systems and the occupants themselves. What’s the set point of the thermostat? How long are the showers in use?

A cost analysis showed the Sustainable Village homes were competitive with other energy efficient building in the Interior — averaging about $185 per square foot, including water and wastewater, electrical, and roads (not including land).

CCHRC also monitored soil temperatures at the homes to study the effects of different foundations on the ground. The two western homes are built on permafrost, or permanently frozen ground, only 2-3 feet deep in the summer. The trick when building on permafrost is to isolate the house from the ground, so heat doesn’t leak into the soil and thaw the frozen ground (which can cause expensive structural problems). These homes used experimental foam raft foundations, steel floor joists with a thick layer of polyurethane spray foam designed to protect the permafrost. Sensors underneath the house show that the foundations are working so far: the temperature at 4 feet deep has risen less than 5 degrees, and at 24 feet has remained the same.

See the full report on first year performance of the homes here.

What is stack effect and how does it affect your home?

How does stack effect work? See for yourself.

Stack effect (also called chimney effect) involves airflow into and out of a building caused by indoor and outdoor air temperature differences Everything starts with the fact that warm air rises and cold air sinks. In winter, your house acts much like a bubble of warm, buoyant air sitting on the bottom of a sea of cold, dense air. This creates a pressure difference, one of the key factors you need in order to have air flow. The actual distribution of pressures inside the house can vary, but generally the pressure is positive toward the top floors and ceiling (meaning air wants to escape outside) and negative towards the bottom floor (meaning air wants to come in). To complicate matters, a taller structure such as a multi-story house will contain a taller column of air that will produce greater pressure differences.

The other key factor allowing for airflow is a pathway for the air to move between the regions of differing pressures, which in your house means leaks in your building envelope. Things are fine if you have no air leaks, but even the tightest homes have some air leaks. As warm indoor air leaks through the walls or roof, it cools and deposits moisture along the way. The problems don’t necessarily stop there, however. New air to replace the air lost must come from somewhere. Replacement air will tend to take the path of least resistance. Typically air is drawn in through the lowest regions (the negative pressure zone) of the house, which is why problems with soils gases, such as radon, tend to increase in winter. Replacement air isn’t always just drawn in through the lower parts of the structure. Air can also infiltrate through poorly sealed or malfunctioning combustion appliances such as wood stoves and boilers, or plumbing traps that have dried out and are therefore no longer able to provide an air seal to the septic system.

The key to reducing potential problems with stack effect is good air sealing around penetrations in the building. If you are considering sealing air leaks in your house, it’s very important that you start at the top. If you start at the bottom, then you might be increasing the chances that air leaking out of the top will pull air from other sources such as combustion appliances. Some common air leakage points in the positive pressure zone of the house (if not properly air sealed) can include: can lights, chimneys, plumbing vents, wiring penetrations, bath fans, and range vents. Always be sure that you have a functioning carbon monoxide detector in your home and that your boiler and wood stove have a dedicated source of combustion air.

Arctic Wall is a new energy efficient construction option in the Interior

The Arctic Wall is an airtight double-wall system using cellulose insulation and is designed to allow water vapor to diffuse through the wall.

CCHRC recently tested a wall construction technique in the Interior that provides very high levels of insulation to maximize energy efficiency. The Arctic Wall is an airtight double-wall system using cellulose insulation and is designed to allow water vapor to diffuse through the wall.

The system was designed by Fairbanks builder Thorsten Chlupp and uses some of the principles of the REMOTE wall—another super-insulated building technique that places the majority of the insulation outside the load-bearing wall.

Conventional cold climate construction calls for a vapor retarder on the warm side of the exterior wall. This vapor retarder typically consists of a layer of tightly air-sealed 6 mil polyethylene plastic sheeting, which keeps water vapor generated in the living space in winter time from getting into the exterior wall cavities. Installing a traditional plastic vapor retarder properly requires a high level of detail around all penetrations to prevent air and moisture movement through the wall assembly. This is a known weak spot for conventional cold climate construction.

The Arctic Wall, on the other hand, has no plastic vapor retarder. Instead of stopping moisture movement with a barrier membrane, it works by remaining permeable so water vapor can move through the wall with the seasons, creating a super-insulated wall that can also “breathe”.

The key components of the Arctic Wall include:

an extremely tight building envelope to prevent air leakage and moisture transport via air leakage through the wall
the majority of the insulation outside the structural framing and air barrier
a wall that is open to water vapor diffusion that has enough capacity within the insulation to absorb and release a heating season’s worth of water vapor without succumbing to moisture damage

Chlupp’s system under study by CCHRC contains a 2×6 interior structural wall filled with blown-in cellulose with taped sheathing and a vapor-permeable air barrier (Tyvek HomeWrap) wrapped on the outside of that sheathing. Spaced a given distance depending on desired insulation thickness from the 2×6 inner structural wall, a 2×4 exterior wall is installed and wrapped around the outside with another air barrier membrane. The space between the two walls is then filled with 12 more inches of blown-in cellulose. See diagram for details. Depending on thickness, a superinsulated wall of this type can attain R-values of 70 or more, more than three times a traditional 2×6 wall system,

CCHRC monitored the Arctic Wall’s performance over 13 months by placing temperature, moisture and relative humidity sensors in the walls. The goal was to determine whether the conditions would support mold growth, and how moisture would move through the walls.

Test results indicated that both temperature and relative humidity levels in the walls were not sufficient to support mold growth. Neither side of the air barrier covering the exterior of the 2×6 structural wall ever approached the dew point (the point at which vapor condenses to water), indicating the structural framing is well protected from moisture.

The relative humidity of the bathroom wall (the one likely to see the most moisture) never exceeded 65%, staying well below the risk level for mold growth.

CCHRC also used moisture modeling software to predict how the walls would perform over a 9-year period, which showed that humidity levels and moisture content within the walls should not reach a level where mold growth would be a concern.

Also noteworthy was the direction of moisture transport in the Arctic Wall—walls dried to the inside in the summer and to the outside in the winter. This is not possible with conventional cold climate construction.

The Arctic Wall is a specific system whose components must be carefully engineered and built to ensure proper performance and moisture management. Based on CCHRC testing, the Arctic wall has done very well in Interior Alaska and provides a new option for a super-insulated house design.

Read the snapshot and full report on the CCHRC website at http://cchrc.org/arctic-wall

New videos on mitigating radon in your home

How to mitigate radon in new construction

The hilly areas containing fractured schist and rock around Fairbanks are known for having high concentrations of radon. A good radon mitigation system will ensure healthy indoor air quality. Your single best chance at dealing with radon issues is during new construction.

In this video, Ilya Benesch, building educator at the Cold Climate Housing Research Center, demonstrates the essential steps of installing a radon mitigation system for a slab-on-grade foundation.

The video follows EPA guidelines for installing radon mitigation systems found here:

http://www.epa.gov/radon/pdfs/buildradonout.pdf

Examining a radon mitigation system

In this video, Ilya Benesch visits a construction site and explores how the contractor has installed a radon mitigation system.

The project was funded by the University of Alaska Fairbanks Cooperative Extension Service. For more information about radon, visit: www.uaf.edu/ces/energy/radon.

How do I keep dust, smoke and other particulates out of the house?

A house should manage indoor air quality by regularly exchanging stale “used” indoor air with fresh outdoor air. You also can improve indoor air quality by avoiding unnecessary sources of contamination, such as restricting smoking to outdoors, storing fuels outside, and selecting low-VOC paints and furnishings. During the year, the air in the Interior can contain particulates from wildfires, wood smoke, dust, pollen, car exhaust and other sources that cause you to shut the windows. That’s where filtration systems can help.

Air filtration options

When it comes to indoor air filtration, the best choice for you depends on many factors, including the size and tightness of your house, your existing ventilation system, your sensitivity, and the amount of particulates and other contaminants in the air. Be aware that irritating and harmful particulates don’t just come from outside but also inside — sources like tobacco smoke, animal dander and mold spores. Other contaminants include gases in paints, carpets, cleaners and other household products. The most common filtration systems are mechanical and target particulate matter. Prices range from about $200-$300 for a one-room portable filter to $6,000-$8,000 for a heat recovery ventilator installation with filtration.

Standalone filtration

The simplest system is a standalone air purifier, which contains a fan and filter elements all in one unit and can be plugged into the wall. These systems are designed to be portable and recirculate air in a single space, and will reduce pollutants like allergens, pet dander and dust from that space. These work well in homes where air quality problems are isolated to one or two areas.

Multiple room air cleaners

Air filtration systems that can serve multiple rooms or even the whole house typically cost more and will require an in-line fan and ductwork, but tend to be more effective.

Keep in mind that whether large or small, filtration systems by themselves don’t introduce fresh outdoor air, but they can provide air cleaning and heat distribution. Whole house systems may be a good option for those with bad allergies or respiratory problems.

Many homeowners who heat primarily with wood install small circulation systems, with an in-line fan and ductwork in just a few rooms to move heat around the house, said Richard Musick, of Ventilation Solutions LLC. The size of the fan is based on how much air you want to circulate.

“If it’s only a couple of rooms, you can get away with a 200 cfm (cubic feet per minute) fan. Big houses can require up to 900-1,500 cfm,” Musick said.

Heat recovery ventilator filtration

While new HRV systems often have high levels of built-in filtration, older models are generally only equipped with coarse debris filters whose primary purpose is to keep the core and motors clean. To help ensure good air quality, a simple filtration system can be attached separately in line with the warm-side supply port on the HRV. All the HRVs at CCHRC have a prefilter to catch the big particles, a main particle filter to catch small particles, and a carbon filter to remove odors, aerosols and VOCs. These filters can be found at HVAC and hardware stores, and are inexpensive and easy to replace. Note that the carbon filters typically need to be replaced more frequently than other air filters.

Rating

Filtration systems are measured by a MERV rating — or minimum efficiency reporting value — which goes from 1 (traps bigger particles) to 20 (traps the smallest particles). You pick a MERV rating based on what you’re trying to filter. For example, MERV 1-4 will take care of pollen, dust mites, and most animal dander, while you’ll need at least MERV 13-16 to filter out smoke particles. HEPA (high efficiency particulate arresting) is in the 17-20 range, removing more than 99 percent of tiny particulates such as carbon dust from the air.

Typically MERV 15 represents the upper limit for residential HRV systems as anything finer may restrict too much airflow. The EPA Office of Radiation and Indoor Air notes that filters with MERV ratings between 7 and 13 are capable of reducing unhealthy particulate matter almost as well as HEPA filters. Additionally, activated carbon filters can be used to neutralize smoke and VOCs.

House tightness

Homes built today are more energy efficient with better insulation and higher levels of air tightness than many of the homes built in previous decades. Building codes now require mechanical ventilation systems for all new residential construction in most if not all northern states. This is simply because uncontrolled air leakage can no longer be counted on to provide the fresh air needed to keep a home healthy. Generally speaking, the highest performing ventilation systems available today will include balanced and regulated fresh air exchanges, in combination with air filtration.

No matter what system you get, check to see what type of replacement filters are required. Some models may use proprietary filters that are more expensive to replace or have more limited filtration capacity.