Creating positive pressure to combat allergies

3 years ago

Background

I am extremely sensitive to ragweed pollens and I suffer during summer and fall every year. [1]

I already have 10 air purifiers spread out around my 2400sq ft house, and while my symptoms are much better indoors vs outdoors, I still experience symptoms indoors. [2]

Hypothesis

An article I read [3] suggests that air purifiers may help in reducing PM2.5 around 75% vs the outdoors but to achieve 100%, a positive air pressure is necessary indoors. The 75% reduction tracks with my experience.

Though my home is new (2015 built) and well insulated, I think outside air is entering my house for a variety of reasons:

This is normal - I think studies say between 30% and 150% of the air in the building gets replaced with outside air over an hour
Pressure differential between inside the home and outside due to heat (it goes up to 110F in the summer) or wind brings in air
I have 6 exhaust fans in my house (kitchen, laundry, 4 bathrooms). Each bathroom’s exhaust fan pushes out 80CFM. If all exhausts are running, I might be exhausting 500 CFM out of my house, which needs to get replaced somehow.

Question

I believe that my issues with allergies indoors can be solved by creating a slight “Positive Pressure” inside my home to prevent polluted air from entering through my building envelope. I have no background with HVAC systems however and need help to figure out what system I need.

What systems could you recommend to help create positive pressure in my house? I’m imagining something like somehow pumping in air into my house (after filtering the outside air with a HEPA filter, of course). This is similar to what was done in the article or how Tesla’s Bioweapon Defense Mode works in their cars[4]
How can this positive pressure intake adapt as I turn on/off some of the exhaust fans in the house? If I pump in too much air, it might increase my heating/cooling bill, but if I pump in too little, it might not be enough to compensate for the exhaust
Is it possible to modify my exhaust fans to compensate for the air loss by also bringing in air via something like an ERV?

Additional details

[1] I’m positive this is seasonal allergies and not mold or any other issues. I live in the Sacramento Valley region which is known for really bad ragweed allergies. The severity of my symptoms correlate with local ragweed pollen counts and with symptoms of friends. I also feel much worse outdoors than indoors. I also feel worse without air purifiers indoors. Whenever I leave the region, my symptoms go away completely. I have gone to multiple allergists, tried a variety of allergy medications/sprays, allergy shots, etc, and while things gave some relief, I still don’t feel normal. I think my best bet is improving indoor air quality.

[2] One reason I know that my air purifiers are not perfect is that during wild fire season, I still smell a significant amount of smoke inside (both via smell and higher air particulate counts). The air purifier helps a lot, but the effect is maybe a 75% reduction like that AirGradient article above stated.

[3] https://www.airgradient.com/blog/air-purifier-vs-positive-pressure-fresh-air-system-an-unfair-battle/

[4] https://www.notateslaapp.com/tesla-reference/1273/tesla-bioweapon-defense-mode-what-it-is-and-how-it-works

Sort by:Oldest

Comments (2)

klem1
3 years ago
Your starting point is hire an air quility engineer to assess the home and existing air handling equipment. For a price the engineer will give you options with their pros and cons. Commercial air conditioning contractor can give you cost estimates from those plans. I would expect the positive pressure solution to be a single make-up air with max cfms of all exhausts combined and controlled by a barometric pressure differential device. Pollen control can be handled with proper hvac filtration. Meanwhile to get as much relief as possible with existing equipment use filters rated at least MERV 10,higher if filter racks will hold thickness. Whatever filter used must fit tight enough to prevent air detouring around them. Remediation plans should include 4" thick filter holders for hvac system which allow using high MERV during pollen season. Very few if any residential hvac contractors are equipped to do what you need. Look for commercial contractor that does clean rooms and such.
PRO
Charles Ross Homes
3 years ago
Sometimes remediating one problem can give rise to another.

While a positive pressure ventilation system will reduce the potential for infiltration of outdoor pollutants, it will also drive conditioned indoor air into stud cavities. Depending on the dewpoint of the indoor air and the temperature of the back side of the exterior wall sheathing, that could result in condensation with attendant mold and mildew growth.

I suggest you consider modifications to maintain neutral pressure rather than positive pressure. To that end, I'd start with a blower door test and a duct blaster test to infer outdoor air infiltration rate and to measure duct leakage. Then air seal as needed and re-test. Once you've got the post-air sealing data, you'll be in a better position to design an appropriate make-up air system. If you want make-up air filtered to the extent indicated above, you'll likely need a commercial HVAC contractor with hospital HVAC experience.
Related Professionals
Atlanta General Contractors · Hopkinsville General Contractors · Norfolk General Contractors · Burlington General Contractors · Hempstead General Contractors · Westerly General Contractors · Elko General Contractors · Belleville Home Remodeling · Rocky Mount Home Remodeling · Beaumont Home Remodeling · Detroit Home Remodeling · Evanston Home Remodeling · Lawrence Bathroom Remodelers · Erie Bathroom Remodelers · Everett Bathroom Remodelers