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Healthy Home Basics - Heating and Cooling

By HHI Staff

From The Healthy House Answer Book: Answers to the 133 most commonly asked questions. Questions 64-71.


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64. Why don’t you like fireplaces or gas ranges?


Actually, we don’t like most fuel-burning appliances—fireplaces, wood stoves, gas ranges, oil furnaces, space heaters, water heaters, boilers, etc. Many people think the reason we don’t like them has to do with fuel leaks. While oil or gas leaks certainly can pollute a house, we’re much more concerned with poor chimney function. Whenever you burn something, you have combustion by-products with which to contend. And, it isn’t healthy to have any combustion by-products indoors. The worst offenders are unvented appliances because they have no chimney whatsoever, and they dump combustion by-products directly into the indoor air.


You might think that if a fuel-burning device is connected to a chimney, the situation would be better. Well, in many cases it is—but in many cases it isn’t. You see, chimneys don’t always function correctly. The combustion by-products (which are warm) rise up through a chimney because warm air rises. You can actually measure a slight upward pressure (called a draft) inside a chimney. Problems occur when there's a negative pressure (that wants to pull in) within the living space that’s greater than the draft pressure (that wants to push up and out). If that’s the case, air can come down the chimney, and the combustion by-products can’t go up. When this occurs, they spill into the living space.


If there's a complete reversal of flow in a chimney (downward), it’s called backdrafting, and all the combustion by-products enter the house. In many cases, the draft is only partially affected, and some combustion by-products go up the chimney while some enter the living space. This situation is called spillage.


Backdrafting and spillage are actually quite common. In some houses they’re regular occurrences. For example, we’ve all smelled wood smoke indoors—smoke that should’ve gone up the chimney. Experts estimate that 50-80% of chimneys have the potential to malfunction.


Sometimes chimneys don’t work because of poor design, lack of maintenance, or damage. But, an increasing problem has to do with very small air pressure differences. A typical draft pressure in a chimney is often less than 5 Pascals (Pa.). A Pa. is a tiny unit of air pressure. (There are over 200,000 Pa. of pressure in an automobile tire.) If any device is blowing air outdoors, it can cause a very slight negative pressure in the entire house. (Exhaust fans, clothes dryers, and central vacuums have all been implicated.) If that slight negative pressure is more than 5 Pa., you can have chimney problems. There are a number of factors that come into play (house tightness, temperature, wind conditions, etc.), but a Canadian study found that about half of all houses would have a problem if a typical kitchen-range exhaust and clothes dryer were operating at the same time.


65. What’s so bad about combustion by-products?


Different fuels release different combustion by-products, but none are good to have indoors. Wood smoke may have a pleasant aroma, but it probably isn’t any better for you to breathe than tobacco smoke. Common combustion by-products include carbon dioxide, carbon monoxide, formaldehyde, nitrogen oxides, particulates, sulfur oxide, water vapor, and various hydrocarbons. Some are worse than others.


For example, carbon dioxide isn’t particularly dangerous—at least not in the concentrations typically found in houses. While water vapor doesn’t sound too bad, it can certainly cause problems. That’s because burning a pound of fuel can release almost a pound of water vapor. If backdrafting or spillage are chronic problems, enough water vapor can enter the living space to cause mold or mildew growth.


Carbon monoxide is colorless and odorless and is, by far, one of the worst pollutants found indoors. The reason for this is, it's particularly deadly at fairly low concentrations. Several hundred Americans die each year indoors due to carbon-monoxide poisoning. Fortunately, most cases aren’t serious enough to kill people. But, low-level carbon-monoxide poisoning seems to be a very common cause of flu-like symptoms such as nausea, malaise, headache, etc. In one study, 24% of people who thought they had the flu didn’t. They were actually being poisoned by exposure to a low level of carbon monoxide.


It’s been found that over 19% of the children in wood-heated homes have allergies, compared to only about 3% in houses with other forms of heat. Wheezing and coughing are also more common in wood-heated homes. Think your gas range is OK? Think again. There are studies showing that children are more likely to have respiratory symptoms if gas is used for cooking, and women who cook with gas have a significant increase in symptoms such as wheezing, waking with shortness of breath, and asthma attacks. They’re also twice as likely to have impaired lung function than women who cook with electric stoves.


66. Are there any fuel-burning appliances that are safer than others?


Actually, there are some that are quite good. These all have one thing in common—they have totally sealed combustion chambers. Here’s what happens inside a regular gas furnace (or boiler, or water heater): air moves from the living space into an open combustion chamber, where the gas and air mix, and are burned. Then, the combustion by-products rise out of the chamber up into a chimney and leave the house.


Here’s how a sealed-combustion gas furnace works: air is pulled from the outdoors through a sealed intake pipe, into a sealed combustion chamber, where it mixes with the gas and burns. Then, the combustion by-products are blown outdoors by a fan through a sealed exhaust pipe. The entire process is sealed, an exhaust pipe is used instead of a chimney, and there’s no way combustion by-products can enter the living space (unless something is broken).


Most major furnace producers offer high-efficiency sealed-combustion gas furnaces. There are also sealed-combustion water heaters and sealed-combustion boilers—if you have hot-water heating. Plus, most gas-fireplace manufacturers offer at least one sealed-combustion model. Sealed-combustion gas fireplaces are often called direct-vent fireplaces. If you plan to use gas for heating, we believe sealed-combustion appliances are the only way to go.


67. Are electric furnaces and water heaters inherently healthier?


Electric furnaces operate somewhat like a toaster. They contain a heating element that warms the air. Electric boilers and water heaters also contain heating elements. Electricity is convenient to use—but it can be an expensive way to heat a house, or to heat water.


Heat pumps use electricity more efficiently, so they’re often more cost-effective. Plus, they can provide both heat in the winter and air conditioning in the summer. Some heat pumps have an outdoor unit that pulls heat from the air. Geothermal heat pumps pull heat from the earth. Heat-pump water heaters are also available.


Electric appliances are sort of a mixed blessing. Their biggest health advantage is there are no combustion by-products. But it should be remembered, combustion by-products aren’t a problem with sealed-combustion appliances either. Although in most cases fuel leaks aren’t as serious a problem as combustion by-products, electric appliances will never leak any fuel. But, they can be surrounded by electromagnetic fields.


68. What’s the best type of heat for a sensitive person?


Sensitive people can react to all kinds of things that aren’t bothersome to healthy people. For example, if dust falls on a hot surface in a furnace or on a radiator it can burn. Granted, this isn’t a serious issue for most people, but the tiny amounts of combustion by-products released by burning dust can bother some who are sensitive. Certain individuals have even been known to react to the small amount of odor released by a warm fan motor in a furnace.


We’ve found that hot-water heating is a good choice for sensitive people. Sometimes just one boiler can serve radiators, a radiant-heating system in the floor, and also provide hot water for all your indoor needs.


Baseboard heaters are often well tolerated. We’ve used them successfully in several houses for sensitive people. They have a metal case with an inert baked-enamel finish. However, some people have had to run them for 2-3 days on high heat to burn off any minor contaminants. They run on electricity, so they can be expensive to operate if you live in a cold climate and your house isn’t particularly well insulated.


69. Is using duct tape a good idea?


Sealing duct joints is a very good idea, but duct tape isn’t the best material to use. In the not-too-distant past, sheet-metal ductwork was assembled with a few sheet-metal screws, and nothing special was done to the joints between the different pieces. Then, people started sealing the joints with duct tape—only to find that it didn’t last very long. In some cases, duct tape (even the more-expensive aluminum-foil type) falls off after less than a year.


Most experts now recommend using duct-sealing mastics. They’re much more durable and longer lasting than tape. We prefer the water-based versions. They're about the consistency of mashed potatoes. We've applied them in a number of ways including smearing on a joint with a gloved hand, using a brush, and troweling.


Sealing ducts is a good idea for several reasons. For example, sealed ducts are more energy efficient. It isn’t unusual to find that 20% of the air is leaking into, or out of, a typical duct system. If the ducts are in an attic or crawl space, then you’re blowing air into and sucking it out of those spaces—rather than moving all of it into and out of the living space. Leaky ducts can also be unhealthy. There are many cases where particles of insulation from an attic, or mold spores from a crawl space, are sucked into leaky ducts and blown into the living space. Leaky ducts can also cause enough of a pressure imbalance in a house to result in backdrafting or spillage.


70. Should heating/cooling ducts be cleaned occasionally?


You’re going to be breathing the air that passes through your ducts. So if they’re dirty, they should probably be cleaned. Some ducts get very dirty very quickly, but others remain relatively clean for years. If ducts are leaky, they can suck pollutants into them. If the living space is polluted, airborne contaminants can be pulled into ducts with the air that’s to be heated or cooled. All this dirty air can coat the inside of the ducts—if there isn’t a good filter to capture it.


Most major cities have duct-cleaning services listed in the telephone directory. They typically use a high-powered truck-mounted vacuum connected to a long hose that’s snaked through the ducts to suck out any dirt and debris. Some systems use rotating brushes, and some operators like to spray the inside of the cleaned ducts with a disinfectant or sealer. In general, we feel cleaning ducts periodically can be a good idea. However, we don’t like the idea of spraying any kind of chemical into them. Just stick with the vacuuming.


In the last few years, a product called ductboard has become very widely used instead of sheet-metal ducts. We don’t like it at all because its fiberglass lining is directly exposed to the airstream. As a result, it can contaminate the air you’ll be breathing with glass fibers, as well as with outgassing from the formaldehyde-based resin. Ductboard is also virtually impossible to clean. Round, flexible, plastic-lined ducts are also popular today. They don’t outgas very much, but sensitive people often special-order them with an aluminum-foil inner liner.


71. What are the advantages and disadvantages to ductless heating and cooling systems?


Hot-water heating systems don’t have the problems associated with leaky or dirty ducts. Plus they can be quieter, and many people prefer the fact that air isn’t being blown around. Radiantly heated concrete or ceramic-tile floors are very popular because they feel warm to walk on. Although they aren’t common, some radiators can be used for cooling by running chilled water through them.


Several companies make small wall-mounted air-conditioners (or heat pumps) that use no duct work. These mini-split systems have an indoor unit that hangs on a wall, and an outdoor unit that looks similar to that used with a conventional central air conditioner. They can be very effective in an existing house where ductwork would be difficult to install.


The big disadvantage to ductless heating and cooling systems is the fact that they can’t be fitted with air filters. While most forced-air heating/cooling systems really don’t have very good filters, at least you have the option of adding one. In reality, you can’t always avoid ducts completely because, if you’re interested in ventilation—and we think you should be—it will usually require some.


(Note: This article is part of the original HHI Archives, and was believed to be accurate at the time of writing. The views expressed in this article are those of the author, and do not necessarily represent those of The Healthy House Institute, LLC.)


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Healthy Home Basics - Heating and Cooling:  Created on February 3rd, 2008.  Last Modified on February 28th, 2011


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