central air filtration

[Bob Ballard]

This is my first post so please overlook any mistakes. I am planning to install central heat and air in my shop.My concern is return air filtration.I am considering oversizing the filter box and using better filters,but I have no idea how much larger to go nor what filter to use.

 

[Mark Jundanian]

Will you also have dust collection at your machines and will you also be using stand alone air filtration unit/s?
Or are you intending that the central air system would perform all the filtration task?

 

[Bill Boehme]

I think that the first thing is to have a good dust collection system to collect as much dust as possible at the source. For your central air conditioning I think that it would be a good idea to use as large a filter as you can get and get one with a high MERV rating. A pre-filter might be useful to prolong the life of the main filter.

 

[Keith Mombourquette]

My shop is about 620 sq ft, and it is located in the basement of my garage, with a walkout on one side. I have a small, high efficiency, direct vented, natural gas fired furnace which is located in the shop and services only the shop . We have a second natural gas furnace for the house. The shop furnace draws air from near the floor in one corner of the shop and circulates warm heated air throughout the shop. I use an Oneida Gorilla cyclone based dust collection system to collect dust at the source of all my machines, and I use a drop from this system to connect my random orbit sanders and the like, so I try and reduce the amount of dust the the shop air, but it is still dusty at times. On the inlet to the furnace, the installers gave me a filter box which holds 3 filters in series, each of which are 1"x16"x24". Typically the first one gets fairly dirty, the second one less so, and the one closest to the furnace stays quite clean. When I replace filters, I usually discard the outer filter and move the inside filters out one position, then install a new one closest to the furnace. Depending on what I have been doing in the shop, I do this once a month or two. I use 3M Filtrete filters. I have my furnace cleaned professionally once every couple of years, along with the one in the house. I have had this same system in service for 25 years, and have no problems.

 

[Mike Johnson]

You can build a pre-filter right into the return air filter on the furnace, some of them have two sets rails or you can add a second set of rails for the additional filter. It would be easiest to use the same size of filter that is designed for the return air, or you can build a larger box that would attach to the intake of your return air plenum and use a larger pre-filter.

 

[Bob Ballard]

You can build a pre-filter right into the return air filter on the furnace, some of them have two sets rails or you can add a second set of rails for the additional filter. It would be easiest to use the same size of filter that is designed for the return air, or you can build a larger box that would attach to the intake of your return air plenum and use a larger pre-filter.

Thanks to all for the replies.I do have a 2hp Delta dust collector with an Oneida canister filter and a shop vac dust deputy combo. I plan to have an air filtration unit by the time the gas pack is installed.I am not sure if one prefilter with a second high merv filter or three identical filters is the way to go. what do you guys think?

 

[Gary Beasley]

If you have room for three filters, two prefilters and a high merv would be better.

 

[Bill Boehme]

You need to pay attention to how much the filters throttle the air flow. Three high efficiency filters might be too much of a load for the blower. In any case I would use as large a filter that is practical. I think that two lower effiency pre filters would work fine and put less load on the blower. Use pleated filters. The cheap ones that are just a fiber mesh that you can see through are worthless.

 

[Bob Ballard]

You need to pay attention to how much the filters throttle the air flow. Three high efficiency filters might be too much of a load for the blower. In any case I would use as large a filter that is practical. I think that two lower effiency pre filters would work fine and put less load on the blower. Use pleated filters. The cheap ones that are just a fiber mesh that you can see through are worthless.

I agree,I meet with the contractors later this week.I hope they have some insight because I cannot find any quantitative info online about high efficiency filters and air flow

 

[Roger Chandler]

The service technician for the company that installed and services our high efficiency furnace in the house tells me not to use the high filtration filters. I had the 3M filtrete highest rated installed and he said they do not allow the system to breathe adequately. I have allergies and was trying to help with that issue, but he said it stresses the system, especially when they get a good bit of dust blocking airflow, or one forgets to change often enough.

I think finding the "sweet spot" is a balancing act. I agree with Bill that 3 normal pleated filters is a pretty good way to go. I now use a more open electrostatic air filter which is supposed to capture way more particles. I've not come to a firm conclusion that they are better than the others yet, but they are washable and reuseable and supposed to be a money saver as they are a permanent replacement.

I got an electrostatic pre-filter for my Delta overhead aircleaner for the shop, and it allows more dust to go inside the 3 pocket inner filter than a pleated filter, which is good in one way, but it does mean replacing the 3 pocket inner filter more often, so I suppose there are trade offs. My biggest priority is cleaning the air, and protecting my lungs/sinuses, but sometimes my frugal side wants to use filters far too long.

 

[Bob Ballard]

The service technician for the company that installed and services our high efficiency furnace in the house tells me not to use the high filtration filters. I had the 3M filtrete highest rated installed and he said they do not allow the system to breathe adequately. I have allergies and was trying to help with that issue, but he said it stresses the system, especially when they get a good bit of dust blocking airflow, or one forgets to change often enough.

I think finding the "sweet spot" is a balancing act. I agree with Bill that 3 normal pleated filters is a pretty good way to go. I now use a more open electrostatic air filter which is supposed to capture way more particles. I've not come to a firm conclusion that they are better than the others yet, but they are washable and reuseable and supposed to be a money saver as they are a permanent replacement.

I got an electrostatic pre-filter for my Delta overhead aircleaner for the shop, and it allows more dust to go inside the 3 pocket inner filter than a pleated filter, which is good in one way, but it does mean replacing the 3 pocket inner filter more often, so I suppose there are trade offs. My biggest priority is cleaning the air, and protecting my lungs/sinuses, but sometimes my frugal side wants to use filters far too long.

Thanks Roger.I hope the contractor has some ideas about how much larger to make the filter box and improvements elsewhere in the system for max air flow

 

[Mike Johnson]

An easy way to test your furnace would be to measure the amperage draw of the motor before you add each additional filter. If you install a larger dimension pre-filter box you are providing more surface area for the air to pass through the pre-filter without adding too much load on the furnace blower motor. If you restrict the air flow too much you will drop the total CFM's and run the risk of overheating the blow motor. You could use a simple manometer tube to measure the pressure drop across the filters.