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Thanks, Ian W and bird for your answers cum explanations.
I must admit that it was only yesterday that I realised that the fan on the base of my Newtonian was moving air away from the mirror. To me that meant that most of the air passing through the fan would be from 'outside' the telescope and very little would pass over the base of the mirror. Perhaps I could fabricate a shroud to ensure that the air being moved came from within the tube, over the mirror and out the back but I'm somewhat dubious about doing that.
Two other options would to be reverse the polarity of the electrical connections or to physically reverse the fan. The latter is a problem; the screws securing the fan (which are as loose as a coward in a bun fight) are on the mirror side of the mount. Sheesh!
A question for all:
Some years ago I did a couple of repairs on what are termed 'car fridges'. These, as best I can gather, use something like the 'peltier' to which some of you have referred to produce their cooling effect. Are we talking about the same thing?
Also from memory, the replacement cost of these cooling/heating units was quite reasonable - well, the people for whom I was doing the repairs were quite happy to pay for my labour plus the replacements.
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