My ac system last had regular maintenance/inspection 9 months ago. Normally I have it done every 6 months but due to coronavirus the company I have a warranty with isn't honoring their warranty. And now my electrical usage is about 2x what it should be (according to the power company comparing my usage to my neighbors) and I think the AC is why. I'm located in Florida where it's usually 90+ degrees almost every day. I did an experiment where I covered the sun facing windows in my home and the electrical usage went down by half.

My concern with cleaning the coils is I was told by a tech to never use any chemicals in the AC, not even bleach. Most techs in the past told me you can use bleach or vinegar but this guy told me not to listen to them because any chemicals can damage the coil.

I suppose it's possible that the tech is both right and wrong. Maybe chemicals are always bad but you have to use them to clean the thing?

Can I just toss a lot of boiling water on it and let the gunk go down the condensation drain? I know how to clean a clogged drain line but are there any problems with using boiling water? Or do you have other suggestions?

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    I've never used anything from water from the hose. Perhaps some mild soap like dish soap might help. I don't think I'd use a pressure washer either as those can damage the soft metal.
    – jwh20
    Aug 17, 2020 at 18:18
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    I can't give you a product name, but they have "no rinse" evaporator coil cleaner. You spray on the coil and walk away, the condensate the coils create will rinse the product away. It's good for preventative maintenance. You can find it on amazon or big box home centers. NEVER use condenser coil cleaner on evaporator coils...
    – Gunner
    Aug 17, 2020 at 18:50
  • @gunner maybe this: Nu-Calgon 4171-75 Evap Foam No Rinse Evaporator Coil Cleaner
    – HenryM
    Aug 17, 2020 at 19:42
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    Define "chemical". Water is a chemical. You are chemicals. Are you asking specifically how to do it with only water?
    – isherwood
    Aug 17, 2020 at 20:22
  • @isherwood chemical meaning chemicals harmful to the equipment in this context.
    – HenryM
    Aug 17, 2020 at 20:24

1 Answer 1


Never say never or always because that will always get you in trouble.

Vinegar is an acid--it will eat the galvanized off the drip pan and can attack the fins so vinegar or acid-based cleaners are bad.

I don’t like bleach because it stinks and if not completely rinsed will have your house smelling like a swimming pool for days.

No boiling water the thermal shock can crack fittings.

Now that we talked about what you can’t or shouldn’t do... There are special chemical cleaners made for coils I use a foaming cleaner made by NU-Calgon called NU-brite. You will find coil cleaners at the big box stores made for coils these also clean the dust and grime out of the coil& fins.

Mild dishwashing soap can be used with water but getting all the soap out can be the fun part there.

Never use a pressure washer on a coil or the fins can be permanently damaged. Same with compressed air. A gentle wash with a hose on the outside unit may be the best bet if you do not have the proper chemicals.

Simple green and water sprayed in with a pump sprayer similar to what you use for killing weeds (never use a sprayer that has been used with weed killer on the inside unit).

I have tried many things and found the best option is commercial cleaner. My 2nd choice simple green and water followed with a good clear water rinse.

Yes I have HVAC licenses and your advice is mostly good not to use chemicals that will react poorly with aluminum, or galvanized materials. I usually power down the system to clean them this allows the chemicals we do use to do there job breaking down tree sap, dust, oil dog/cat pee (on outside units) that will damage the fins also. Once I treat the coil I flush it with clear water sometimes a 2nd treatment is needed but not usually on a well maintained system as yours has been.

I use 2 different sprayers on inside units one for the chemical and one with clear water. Making sure the drain stays clear and doesn’t overflow the pan. This should help return your system to peak performance. And don’t forget about your filter. Always a good time to change the filter after a coil clean.

  • Are you saying you use NU-Brite indoors or only outside? I read that it is recommended for outside only. So that would just leave soap and water then?
    – HenryM
    Aug 17, 2020 at 19:28
  • NU brite is a foaming coil cleaner They don’t recommend for indoor use because of the foam overflows the pan a small shop vac takes care of that and is what the factory rep suggested I have been using for both for several years I think my wet dry shop vac is 3 gallon but I only vacuum as it gets to the drain sometimes a little clear water spray and it goes down the drain , if not I suck it up before it makes a mess.
    – Ed Beal
    Aug 17, 2020 at 19:34
  • I also found this (based on a comment above): Nu-Calgon 4171-75 Evap Foam No Rinse Evaporator Coil Cleaner. Seems you can use this one inside or out. Maybe I will try nu-brite on the outside and this one on the inside. Thanks
    – HenryM
    Aug 17, 2020 at 19:41
  • I really like the foaming cleaner , simple green did a good job but took multiple cleanings. You can see the foam pushing out the dirt then it goes white you know you got it all but I have used several of their products and hav been pleased with the results, I found out about nu-brite in a training class ( 4 hour sales pitch) for a particular brand of ac unit the rep came in and gave samples I used the sample on my unit I thought I had cleaned it well , I purchased a gallon and told him if it worked inside I would buy the 2 or 2-1/2 gallon totes that’s when he told me about the vacuum.
    – Ed Beal
    Aug 17, 2020 at 20:06
  • Just in case anybody cares: Been using the nu-calgon evap foam no rinse both inside and out for years now. Pricey but worth it. Works like magic. If it's not shooting out of the can like a laser beam you probably didn't shake the can enough.
    – HenryM
    Oct 31, 2023 at 14:30

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