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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman",serif;color:#002060">Bingo! Jim hit the nail on the head.
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman",serif;color:#002060">The 4 inch filter has a lower pressure drop because of overall greater filtration area due to all of the deep pleats. It also has a lower frequency of filter
change out for the same reason. Using two one inch filters together will impact your flow. It may not affect your performance noticeably, but it will change the system flow, drive up fan energy costs, etc.
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<br>
<a href="https://nordicpure.com/">https://nordicpure.com/</a> seems to have a lot of sizes in stock and they are not too badly priced either on their website or Amazon. I’ve used them for a while and am happy with them. They are available in a wide range of
MERV ratings too.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman",serif;color:#002060">I have a differential pressure meter across my filter. It registers 0-0.25 inches of H<sub>2</sub>O. I let that guide my changeout frequency, which often
is around a year before the pressure drop indicate to me that it should be changed. Ok, yes, I am a Mechanical Enginerd.<o:p></o:p></span></p>
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Jack<o:p></o:p></span></p>
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<p class="MsoNormal"><b>From:</b> Shop-talk <shop-talk-bounces@autox.team.net> <b>
On Behalf Of </b>John Innis<br>
<b>Sent:</b> Monday, December 13, 2021 2:44 PM<br>
<b>To:</b> Jim Stone <1789alpine@gmail.com><br>
<b>Cc:</b> Shop Talk <shop-talk@autox.team.net><br>
<b>Subject:</b> Re: [Shop-talk] Furnace Filters<o:p></o:p></p>
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<p class="MsoNormal">The only real issue is that you will not get as much airflow through a 1" filter of a given effectiveness. Most of the time that's not a big deal. In our previous house we did have an issue with the AC freezing up when it was working
really hard. In that case the solution was a lower effectiveness filter because the box could not accommodate a thicker filter. If you are happy with the performance of the 1" filter and have not had any issues, i'd say stick with it. I do NOT recommend
stacking two one inch filters. <o:p></o:p></p>
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<p class="MsoNormal">On Mon, Dec 13, 2021 at 4:20 PM Jim Stone <<a href="mailto:1789alpine@gmail.com">1789alpine@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">The company that installed my HVAC system a few years ago used a filter box on the return line that takes 20” x 25" x<b> 4”</b> filters, which is an unusual, and thus expensive, size - filters generally run about $25 each - that is not
readily available other than online. During construction, my general contractor just had a cheap 20” x 25" x
<b>1” </b>filter in there that seemed to work just fine. I checked the installation instructions for the furnace and there are no specifications for the filters, other than that they need to be changed regularly, which is getting pretty expensive. Is there
any reason I couldn’t just use 1” filters, which are less than half the price? Maybe even put two of them in the box, a good one first to catch most of the dust and a cheap one like the contractor used as a secondary one. It is a snug fit and I don’t think
there is any danger of them tipping, but two would make it impossible.<o:p></o:p></p>
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<p class="MsoNormal">Thanks,<o:p></o:p></p>
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<p class="MsoNormal">Jim<o:p></o:p></p>
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