My skin and sinuses don’t like dry air, and nothing dries air like heating it: Heat freezing air at 40% relative humidity (RH) to room temperature and the relative humidity drops below 10%, which is as dry as deserts at noon!<\/p>\n\n\n\n
So when indoor heat comes on in the winter I break out the humidifiers. If my living space has a central air handler I install an automatic humidifier on that. If not I have to manually fill portable humidifiers. Which led me to wonder: How much water does it take to bring the humidity in dry air back up to comfortable levels?<\/p>\n\n\n\n
It turns out that the moisture capacity of air is very non-linear with temperature<\/a>: For example, air at 100\u00b0F holds 10 times as much water as freezing air!<\/p>\n\n\n\n Thanks to\u00a0data here<\/a>\u00a0we can see that air at room temperature (20\u00b0C\/68\u00b0F) holds up to 17g of water per cubic meter. So a 1000ft2<\/sup>\u00a0living space with 9-foot ceilings can hold just over 4kg, or 1 gallon of water, at 100%RH.<\/p>\n\n\n\n Humidity in living spaces should be kept below 50%RH because mold really thrives above that level. So when outdoor air is below freezing we need to add half a gallon of water to the heated indoor air of my hypothetical 1000ft2<\/sup>\u00a0living space. But healthy living spaces also exchange fresh air \u2013\u00a0ASHRAE recommends eight air changes per day<\/a>\u00a0\u2013 so if that living space is properly ventilated then we will have to add four gallons of water per day!<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":" My skin and sinuses don’t like dry air, and nothing dries air like heating it: Heat freezing air at 40%…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"inline_featured_image":false,"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":true,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","enabled":false},"version":2}},"categories":[6],"tags":[35],"class_list":["post-837","post","type-post","status-publish","format-standard","hentry","category-handyman","tag-engineering","post-archive"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/david.bookstaber.com\/index.php?rest_route=\/wp\/v2\/posts\/837","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/david.bookstaber.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/david.bookstaber.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/david.bookstaber.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/david.bookstaber.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=837"}],"version-history":[{"count":2,"href":"https:\/\/david.bookstaber.com\/index.php?rest_route=\/wp\/v2\/posts\/837\/revisions"}],"predecessor-version":[{"id":839,"href":"https:\/\/david.bookstaber.com\/index.php?rest_route=\/wp\/v2\/posts\/837\/revisions\/839"}],"wp:attachment":[{"href":"https:\/\/david.bookstaber.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=837"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/david.bookstaber.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=837"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/david.bookstaber.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=837"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}