At the head of the picturesque Loch Tay, renowned for its fishing, the Killin area is a magnet for tourists, hill walkers, and cyclists who flock there to take in the magnificent views.
There are numerous hotels, guest houses and B & B houses - all overflowing with customers in the warmer months and also in the winter when the area becomes a Mecca for winter sports enthusiasts. Whatever the season, these businesses need a reliable supply of constant hot water. And Sonia is on a mission to ensure they have this continuous supply.
"Rinnai infinity water heaters are just amazing with outstanding performance for their size and cost," she says. "On top of that their safety features are impressive plus they are so easy to install - just one pipe in and one pipe out. The Rinnai units are easy for me to handle on my own and that is important for a woman. Some comparable products need three people to lift them.
"The service form Rinnai is excellent too. We get next day delivery from them even here in the remote Highlands. It means we can offer a much faster service to hotels and B&BS, which, as commercial businesses, need replacements directly. Delivery times from Rinnai are unsurpassable." She also praises Rinnai's technical support.
Reliability, of course, is paramount. "I have fitted countless Rinnai units and I can say that we have never had a problem with them in the three years we have been using them - literally no call backs or people complaining about them. On the subject of energy efficiency we have people telling us how much money they are saving on bills since they had them fitted."
Sonia is particularly impressed with the performance of Rinnai's external units having installed one at a shower block in 2010. "If you remember that was one of the worst winters we have had up here in 20 years with extremely hard frosts and the Rinnai coped with the worst of it with no problem at all."
Sonia has recently installed two HDC1500i units into the 20-bed Bridge of Orchy Hotel which sits in a prominent roadside location close to the West Highland Way. "I put in two of the biggest units because I knew demand for hot water at peak times would be huge and they are coping fine with it."
Sonia's first encounter with Rinnai product, however, started with a degree of scepticism on her part. "I was called in to perform an installation at a caravan site which had ordered the units themselves. It was my first sight of a Rinnai unit and I thought that is far too small to cope with the demand. I was proved wrong, of course, and was so impressed I immediately installed one in Grant's Laundry, which is run by my sister. Since then they have gone into all sorts of domestic and commercial buildings, whether fired by Natural Gas or LPG in remote off-grid areas.
"I have worked with Rinnai ever since and will continue to do so. I have put in so many Rinnai continuous flow water heaters in Killin and the surrounding area that we are getting to the point where there are more Rinnai units than inhabitants," she jokingly concludes.
"Rinnai infinity water heaters are just amazing with outstanding performance for their size and cost"
Sonia Hewitt, A C Fraser and Sons