Furnace filters

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Furnace filters

Postby Gilbey » Thu Nov 28, 2013 12:24 pm

We have a Lennox high efficiency gas furnace. When it was first installed, we had a (metal) electronic filter on it. This worked well for several years. A while back, when our AC gave trouble, the tech who fixed it told us that the electronic filter was not the best idea and recommended that we switch to a Filtrete high performance filter that reduces allergens. We have been using the Filtrete for just over a year, changing it every 6 months.

This week, the tech who came to service the furnace told us the furnace was over-heating and that the Filtrete filter was to blame. He said that the Filtrete filter is very dense and deeply pleated to catch as much dust and allergens as possible. This denseness prevents proper air flow through the furnace, therefore the furnace works too hard. The furnace over-heats, which shuts off the gas and the house is then not properly warmed up.

This made some sense to us as we had been finding the house getting quite cold sometime in the early morning hours, even though the furnace appeared to be working.

The tech suggested that we use a different type of disposable filter. Filtrete is quite expensive - the tech told us to get a less expensive pleated filter which would allow air to flow properly.

At this point, we are confused, as the Filtrete came highly recommended. Does anyone have any experience similar to this with Filtrete? Can you recommend a filter we should try? Very much appreciate any advice you can give.
Thanks.
Gilbey
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- Furnace filters

Postby Freon » Sat Nov 30, 2013 3:56 pm

The first thing you need to do is verify that the furnace is overheating. To do this task is very simple. Set the thermostat 5 degrees higher than the house temperature so the furnace comes on. Then immediately go to your furnace and watch the flames. If the furnace is overheating, after several minutes the flames of the burner will go out for a minute or two (while the combustion chamber cools) and then the burner will relight BUT main blower will continue to circulate air in the house even when the burners are off. This cycling (burner ON then burner Off) will continue until the thermostat set temperature is reached and the furnace shuts off.

It is possible your furnace will simply shut off completely if there is an overheat situation. There may be an error code on the control board telling you the error.

If you do see this burner cycling or completelt shutting down while the house temperature is less than the thermostat set temperature, then your furnace is overheating. I will assume the temperature sensor that indicated an overheated situation in the combustion chamber is working as it should.

Next you need to tell us the model number of the furnace and how many filters you have and where they are located. Some filters are in filter grilles and some are only in the furnace near the blower. Sadly many furnaces are installed with too little ducting for return air and that's one thing you need to investigate.

As for filters, they usually go by a MERV number. The higher the MERV number, the smaller the particles the filter will catch AND the more restrictive it will be to air flow. See if you can find the MERV number of the filter you use. There is another number some manufacturers use that correlates to MERV. If you have a MERV 10, I would drop to a MERV 6. Also you may need to change filters more often. As the filter collects particles, it also restricts air flow more.
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- Furnace filters

Postby Gilbey » Thu Dec 12, 2013 6:46 pm

Thank you for replying and providing this information. (Sorry I did not get back to this sooner - have had family medical emergency)

The furnace is a Lennox Elite SureLite G2603-75. We have determined that it is no longer overheating since we removed the Filtrete filter.

Attached to the furnace, where the cold air returns to the furnace, is a Honeywell Air Cleaner. This is the electronic filter with metal mesh screens and larger metal filters - 2 of each. They slide into the Honeywell unit. The screens are closest to the cold air return duct and the larger filters, with all the fine wires, are next to the furnace. We have put these back in for the present time. These are the only filters on the furnace that I am aware of. I am assuming that there are no other filters inside the actual furnace casing.

Are these metal filters adequate? I take them out and wash them every three months. If not, I will look for a different type with the MERV number visible and will change it more often than the instructions say. I cannot see the MERV number on the Filtrete filters that I have.

Is there anything else I should be doing? Again, many thanks for your help.
Gilbey
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- Furnace filters

Postby Freon » Fri Dec 13, 2013 12:09 pm

I know very little about metal/electronic air filters. You might check with Honeywell to see if there is an equivalent MERV rating for your metal filter system.

If you are happy with your air quality then the filters would seem to be adequate. One of the most important jobs of an air filter is to keep your evaporator coil clean. If you have an evaporator coil you could check it to make sure it's clean too. If you find the evaporator coil dirty (restricting air flow) then the Honeywell filters may not be doing their job.
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