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Avoiding Odor Problems with Solar Air Heating Collectors

With a solar air heating collector, the room air circulates through the collector and then back out into the room.  So, any odor that the air picks up from the collector comes back into the room.  Since the collector runs hot inside, there is the potential for some materials to cause odor problems if used inside a collector.

While most people don't report any odor problems, I have heard from a few people who did have odor problems.  As far as I know, all of these problems have gone away over time.  The advice below should help you avoid any potential odor problems.

- Be careful about ANY material you include in the collector -- think about whether it might cause odor problems.  Sometimes a test in an oven set to about 250F can be helpful in identifying materials that cause odor problems.

 

- If the absorber needs to be painted, then paint it with a good quality, high temperature paint.  Rust-Oleum high temperature black barbeque paint is widely available, and appears to work well. 
Paint the absorber with as thin a coat as you can while still achieving good color hiding.  Excess paint thickness just reduces performance and results in a longer time for the paint to cure and become odor free.

 

- Use only silicone caulk in the collector box.  Silicone produces a bit of odor while curing, but it goes away quickly Silicon is a very high temperature material.  I would stick with the "ordinary" silicone as opposed to all the special variations, as I'm not sure what they add to make them "special".

 

- I've used high quality latex paint to paint the interior of the collector frame, and had no problems.  I believe that some wood sealing products can lead to odor problems.

 

- Install the absorber in the collector frame, and let it sit out in direct sun for a couple days before installing the glazing.  This helps to bake and cure the odor out, and also keeps the paint volatiles from coating the inside of the glazing.

 

- you might want to avoid PVC in the collector or outlet ducting.  Some people report an odor from the PVC -- especially at high temperatures.

 

- Some metals that are used in collectors (eg aluminum gutter downspout or aluminum soffit material) come with a high quality, baked on finish.  I've not heard of these materials causing odor problems.  Likewise, black metal insect screening for the absorber does not appear to cause any odor problems.

 

- Use only high temperature insulation.  Polyisocyanurate insulation works well (1).  Don't use polystyrene, as it is only good up to about 130F.  The pink, blue, and white rigid sheets of foam board are normally polystyrene. 
(thanks to David for reminding me of this)

If you have an odor problem anyway, try:

- If its relatively easy to do, take the glazing off, and let the collector bake in the sun for a few days.

 

- Vent the collector output to the outdoors until the odor disappears.  It might help to alternate periods of stagnation (no flow) with periods with the fan or circulation on.  If its difficult to rearrange the outlet venting, you may be able to just cover the outlet, and pull back the glazing a little or open a hole in the collector frame to act as an outlet opening.

 

- I guess that if you have a really really persistent odor problem, you may have to find the offending material and remove it.  I've not yet heard of anyone having to go this far.

 

I'd like to hear from you if you have had odor problems with your collector   Gary...

(1) Polyisocyanurate (sometimes called polyiso) is a high temperature polyurethane based insulation that works well in collectors.  Many lumber yards carry it, but they often don't know it by the name polyiso.  Ask the lumber yard person to look at what they carry -- if its polyiso, each sheet will say polyisocyanurate somewhere on the face.  This insulation is usual a tan color, and normally comes with face sheets -- often reflective aluminum foil.  Its slightly more expensive than the polystyrene, but also has a higher R value per inch.

Gary

March 10, 2010