Tributes from politicians have also poured in for the 47-year-old Goulburn man who suffered a heart attack on Saturday, January 4, after helping his good friend, Geoff Purcell, defend his Batlow district property against the Dunns Road fire.

Goulburn's Saints Peter and Paul's Cathedral was almost filled to capacity for his funeral service. Friends hung rugby jerseys and placed mementos of a sporting and adventurous life.

One of his three older brothers, Warren, clearly remembered his mother, Jan, cradling "the little baby boy with the most beautiful blue eyes".

Their father had left them at a young age. Growing up, the boys enjoyed fierce battles in the backyard, playing cricket and football.

"Dave, being considerably younger, had to quickly learn to stand on his own two feet because we gave him no quarter in the backyard cauldron," Mr Harrison said.

"Dave was blessed with many talents. He was handsome, charming, funny, athletic and intelligent. We all agree he was the smartest in our family, with daylight a distant second."

Mr Harrison said his brother had excelled at all sports, including rugby, cricket and swimming. In rugby he was selected in Saint Patrick's First XV, played for ANU, the Goulburn Dirty Reds, Tumut Bulls and Hawkesbury Agricultural College.

"He was great to watch too. A hard running loose forward, he could really skittle a defence when he got going," he said.

David had loved nothing more than a family get together. The last one in Sydney at Christmas was full of laughing, eating, singing and sailing and left "cherished memories".

Soon after, as he often did each year, he travelled to the Tumut area to spend the New Year with his old school friends, the Purcells. They were like a second family.

Mr Harrison said his brother and Geoff Purcell had managed to save the house and most of the cattle in the fire.

"He could easily have left earlier, as his brothers had encouraged him to do, but he would not leave Geoff on his own. This is typical of Dave - loyal, brave and ready to help," he said.

Police said David suffered a heart attack after going to retrieve water from the back of a ute. Mr Purcell had then driven with him to seek help but the best efforts of emergency services couldn't save him.

Mr Harrison remembered his brother's kind and gentle nature, sunny disposition and "uncomplicated approach to life".

"In many ways he was an ordinary Aussie bloke but to his family and those who knew him well, he was anything but...he was extraordinary," he told the congregation.

Mr Purcell became emotional as he recalled his good friend. Mr Harrison was like "a fourth son" in his family, had worked and lived on their orchard and vineyard at Mittagong and went on sporting tours with them and other friends.

"He always came to the farm (near Tumut) for New Year's and grand final days or for any excuse," Mr Purcell said.

"He loved it there as much as we did and wanted to stay and help us save our house and animals. 'Harry,' I love you mate."

Former schoolmate, Pat Lenane, recalled the man who was big in stature, soft inside and whom a childhood rugby league coach had humourously dubbed 'Biscuit.'

"Every training session he would turn up late, even though he only lived 100 metres from the field, with a biscuit in each hand, one in each pocket and one sticking out of his mouth, so the name stuck," he said.

"...There are people in our lives that we meet that influence us, but there are only a handful that influence us to the point we take something from what they have done or shown us and use it in our life. For me that was 'Biscuit'."

Former Saint Patrick's College captain Rick Archer also paid tribute to Mr Harrison's sporting prowess and passion for problem solving that saw him tackle the hardest subjects at school. He was among the top 10 per cent of NSW students in his HSC year and subsequently undertook an engineering degree.

But he never refused to help a mate.

"(His) legacy of a big smile and open heart touched every student who knew him. He is and always will be our brother," Mr Archer said.

Premier Gladys Berejiklian, Deputy Premier John Barilaro and Deputy Prime Minister Michael McCormack also sent condolence messages.

"David epitomised what it means to be a mate," Ms Berejiklian wrote.

"When a friend needed help, he dropped what he was doing to lend a hand."

Mr Barilaro said Mr Harrison's life embodied loyalty, bravery and mateship and his legacy as an "Australian hero" would continue to inspire.

In a statement, Mr McCormack said Mr Harrison had made a selfless commitment to serving his community.

"David was a gifted man, but more importantly, a genuinely good bloke," he said.

Mr Harrison is also survived by his brothers Peter and Michael, their spouses and nine nieces and nephews. His mother, Jan, predeceased him.