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Question DetailsAsked on 10/25/2015

How much does it cost to have an AC air scrubber installed?

Was told there is mold/mildew buildup in the inside unit. What are my options? What are the typical costs associated with it? Thanks!

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1 Answer


Here is one prior related question with response which I found -

Typical types of units used for HVAC air quality - and installed costs can run from around $1000-3000 range depending on type and size for the effective units (smaller, much less effective units can be gotten for under $1000 but generally are not a real solution). Not all are applicable to or will fit in all types of units, so you will need a Heating and A/C contractor (a system design person, not just a repair tech, so commonly one of the more experienced people in the company) to assess your situation and come up with a fix that should work for you.

Obviously, changing run times and possibly going to either a delayed fan shutdown or continuous fan running or limiting outside air is a much cheaper option than the others - and might serve as an initial test to see if it can be solved that way before investing in a more expensive "positive treatment" system.

In looking back over the following list (which was just stream-of-mind), it looks like I ended up with the more expensive, more technological solutions at the top and the simpler possible initial "trial-and see" ones nearer the end, so perhaps read from the bottom of the list up to see the simple to the more sophisticated possible fixes available. (I did leave out a couple that are not applicable to residential size units)

1) Ultraviolet light exposure on the evaporator to control the growth of mildew and mold

2) high-efficiency electrostatic precipitator and/or HEPA air filters BEHIND (on house side) of evaporator to remove mold becoming airborne at the evaporator - this in addition to air filtration of the incoming air to minimize the incoming dust, which acts as food for the mold

3) ozone generators and hydrogen peroxide "purifiers" - though there is an accumulating amount of medical info that those including one very scary study published in the New England Journal of Medicine and another OSHA warning and a military medical alert, that while reducing or killing bacteria and funguses and molds in the air, can have significant adverse health effects due to the presence of spinoff side effect high energy state chemical compounds and of the agent itself in the air when you breathe it or it coontacts mucous membranes or eyes, which can have significant long-term damage results. Beginning to look like this cure might be more dangerous than the initial problem, especially with long-term exposure. These systems can also cause corrosion of metals in the house - from ducts to silverware to electronics, depending on exposure.

4) separate evaporator air handler evacuation and dehumidification system (basically applicable to independent air handlers only) which, as soon as the air conditioner shuts down (desired house temp attained) then flushes the evaporator with outside air, which is vented outdoors, to totally dry the evaporator off - thereby removing the sustained moisture needed to grow the mold. This is a newer technology, currently used mostly in commerical buildings like hotels where they are afraid of Legionnaire's Disease and similar situations, but I have seen a few tech notes by residential A/C system manufacturers about it, especially for very humid regions.

5) also in that same category - the newer (very rare still) air handler units that use a shot of intense infrared or ultraviolet energy directed at the evaporator at the end of the cooling cycle to kill any mold growth - though requires specially built evaporator with integral units to do that.

6) changing the amount of outside air being blended with the airflow,especially in humid climates. Obviously there are air quality issues involved in recirculating the indoor air, but basically the more humid outside air you bring in the more moisture accumulates on the evaporator, so the more moisture is available to grow mold.

7) a solution commonly used with existing systems is to use continuous (or near-continuous) air circulation - keeping air flowing over the evaporator all the time to dry it out after the cooling cycle, thereby reducing the habitat for the mold. Can work especially well with mini-split interior wall-mounted units.

8) short-cycling can sometimes, with various systems and sometimes requiring a new special programmable thermostat with variable setback range (some thermostats have changeable range, some do not), is to program the thermostat so there is more than a normal spread between system shutdown and start-up temperatures - say maybe 10 degree range rather than 3 degrees, for instance - so the tempeature drop needed before the unit shuts down is much larger, therefore the unit has to run longer to achieve tht drop and hence has a longer cycle.

Answered 4 years ago by LCD

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