We would recommend the ULSA-2 as a replacement for your Reznor ULSA 100. Please click the link below to view the product. https://www.reznor.co.uk/product/rheco-warm-air-heaters/
What would be a good replacement for a Reznor ULSA 100?
Looking to upgrade your old heater? Look here for information on which product is the best like-for-like replacement.