What’s a good number of friends to have? How to stay safe on the Internet? How can you tell if a friend is lying in a text message? How long should you wait before tying the knot with someone? How to dress appropriately in the gym? My Carrier furnace works fine without the air filter in place on the return. With the filter in place it works for a while and then stops with a complaint about "limit, or flame rollout is open" (Carrier unit error 33). What are some next steps I can carry out to narrow down the problem? As Tester101 mentioned (and he really should've made it an answer, because it's at least a partial one), the filter could restrict airflow to the point where your furnace overheats. Hence the 'Limit' error.Trying a cheaper filter, or running without a filter, isn't a good answer. You'll shortly find that the furnace won't run at all, with or without a filter. What this probably means is one of two things, both of which are not DIY in my book.

The first is that your blower unit is going, or is clogged with dust/dirt/pet hair/warm fuzzies/etc. This would require a qualified HVAC professional to replace. The second is that you may have an A/C unit, and the coils are clogged. The second is somewhat DIY-able, but I can't give you directions because I don't know your unit. Mine slides out on kind of a tray, which lets me blow the coils off with compressed air or coil cleaner (which is available as an aerosol at the hardware or home improvement store near you.) Not tending to this risks a furnace fire. That's why it stops. Get it taken care of!Browse other questions tagged hvac furnace air-filter or ask your own question. > Arts & Living > Home and Garden There's No Keeping Pollen Out, But Let's Try to Hold It Down Washington Post Staff Writer Thursday, April 12, 2007 Pollen season -- leaving its telltale yellow film on windowsills, tabletops and cars -- is upon us with a sneezing, itchy-eyed vengeance.

There is no way to avoid the stuff completely -- moving to Antarctica might help -- but there are ways to fight back inside our homes. The closest thing to universal advice from experts is to keep doors and windows shut, especially during the peak pollen hours of 5 to 10 a.m., says Thomas Casale, president of the American Academy of Allergy, Asthma & Immunology, based in Milwaukee. Beyond that, here are some options for clearing the air: Filters that fit over window screens are another low-tech approach to keeping out the allergens. These reusable filters -- some are made of wire mesh, others of plastic -- come in frames up to 11 inches tall that expand sideways for a snug fit. Manufacturers claim they block 90 percent of pollen from entering the home. Until you need to turn on the air conditioning, you can use the fan-only mode on window units or a central system to circulate air, says Mark Connelly, Consumer Reports magazine's senior director of appliances and home improvement.

The fan will bring in fresh air while filtering particulates from outdoors. For more protection, install HEPA (high-efficiency particulate air) filters in window air-conditioning units or central air and heating systems. These filters, made with glass fibers, are designed to trap more than 99 percent of pollen, dust and tobacco smoke. A one-inch-thick HEPA filter for HVAC units costs much more than a conventional model. At Strosniders hardware stores in Montgomery County, for example, standard filters start at $1.69, while the least-expensive HEPA version is $17.99. ac to dc power supply designRetrofitting a forced-air ventilation system with larger HEPA filters can also be costly.home ac unit comparisons To remain at peak effectiveness, HEPA filters must be changed at least every month, perhaps more often, because they trap more pollutants than standard filters. outside ac unit won turn on

"If you don't [change them], the furnace or the blower motor can overheat or the air conditioner can ice up," says Bob Nibert, service manager at Academy Heating and Air Conditioning in Rockville. Room air purifiers, about the size of dehumidifiers, filter air within a closed space. They use HEPA filters or other technology to clean air before recirculating it. Larger spaces need larger units; most specify the maximum area they can handle. For best results, they should circulate the air several times an hour. "If you are going to focus on a particular room, focus on the bedroom, because it's where you spend the most time," allergist Casale says. But Connelly of Consumer Reports has doubts about a single-room approach to air filtration. "If you have pollen as an issue, it makes more sense to get a whole-house cleaner" in the HVAC system. Remove pollen regularly from household surfaces by dusting with a microfiber cloth or a slightly damp rag, says Philip Doyle, owner of the MaidPro franchise in the District's Adams Morgan neighborhood.

Clean "top to bottom" to keep particles from flying around. Although Web sites offering products geared to allergy sufferers feature special cleaning sprays such as AllerDust, Casale says, a regular dusting cloth or a feather duster sprayed with furniture polish will pick up more particles without sending them airborne. Once surfaces are clean, damp-mop the floor or use a vacuum cleaner with a HEPA filter. "Pollen is a very large thing and tends to settle out very quickly; it tends to drop to the floor," Connelly says. If you are particularly sensitive to pollen, shower and wash your hair before bedtime every night to remove allergens you may have brought indoors. "If you have been outside for a while and you don't shampoo your hair, the pollen will stick to your pillow" and be inhaled or get in your eyes, Casale says. Though it may not be practical to give pets who spend time outdoors a nightly bath, they should be brushed regularly, ideally by someone who doesn't have allergies.