Hi Brian,
I'd recommend the ETI TN1:
Currently available via
Amazon for £17 including delivery.
It is as accurate as other IR thermometers costing many times more and is a convenient size/style for the task of balancing radiators.
Despite the Amazon title there is no laser targetting dot however don't be put off by this as they are all but useless for close-up temperature measurements because of the parallax errors due to their position.
A couple of tips regarding its use:
- The TN1 has a target:spot ratio of 1:1 which means that, for example, the measurement spot on a surface 5cm away will be 5cm in diameter. You want to therefore ensure the thermometer is close-up to the item being measured in order to ensure accurate targetting. This is one area where paying more money will give better ratios (however for balancing radiators this benefit is largely redundant).
- Put black insulating tape on the target being measured as, with metals in particular, the emissivity can vary significantly which will affect the accuracy of IR thermometers. Like most, the TN1 is set to an emissivity of 0.95 by default (this can be changed), which corresponds very closely to that of black insulating tape. Furthermore, the tape ensures consistenty across all radiators.
Practice a bit first to ensure you are getting accurate readings. You are aiming to get the highest reading possible as this necessarilly corresponds with the most accuracy. You'll soon get the hang of positioning to get the same accurate reading over and over.
There's plenty of discussion in
this recent thread which might be of interest (the focus on balancing occurs further down the thread).
Good luck!
Mathew