There were so many delays to the cost controls for the RHI scheme that the renewable heat industry would nearly "stop taking the department seriously", claims Alan Hegan.

Image source, RHI Inquiry

Boiler installation firms didn't know the reason for the continual delays and the pushbacks to the implementation date for the changes were "surreal".

"Any other scheme I've ever worked on there's a deadline - and the deadline's the deadline - that's it," he adds.

Such was the demand for biomass boilers through the RHI scheme in the summer and autumn of 2015 that plumbers from the Republic of Ireland were called in to work on installing them, says Alan Hegan.

During that busy period, it would take about two-and-a-half weeks from a client ordering a boiler to having it installed.

Image source, Getty Images

Ordinarily it would've taken up to eight weeks but the process had to be sped up because "there was no option to run over the deadline".

Some plumbers from "as far away as Limerick... were staying in a hotel local to us", says the witness, adding that his firm wasn't the only one with workers staying in that same hotel.

There was never any request from DETI civil servants for those within the renewable heat industry to keep quiet about delays to the RHI scheme, says Alan Hegan.

He admits that he would've spread the news widely when he received it from officials in the department.

As soon as he heard of a one-month delay in the changes from October to November he called potential clients who were "in a queue" to tell them: "Do you still need a boiler? We've got another month - we can do it for you."

He says that's a "commercial reality" and there's "Nothing untoward about that".

Competing boiler installers wouldn't have shared information directly with one another, he says, but there were indirect channels of communication - subcontractors who worked for multiple installers and suppliers who worked across the industry, for example.

Alan Hegan's order book for biomass boilers was full by the end of July 2015 - so much so that he even postponed a family holiday to deal with the amount of work he'd taken on.

Cost controls were due to be added to the RHI scheme at the start of October that year but the implementation date was delayed on a few occasions.

Word was spread to potential clients about the impending changes.

Image source, PA

Every time Mr Hegan heard about a delay he reopened his book and took more orders - it was "the busiest ever I've ever been in my life" and the renewable energy industry was "full pelt" and - pun possibly intended - "overheated".

The phones were ringing off the hook with up to 100 calls a day - his voicemail box was so full of messages that it couldn't accept any more.

He says he told DETI about the sharp rise in demand but that didn't appear to prompt any concern among the civil servants who were working on the scheme.

Northern Ireland's renewable energy industry is an "interconnected spider's web" and information about the changes to the RHI scheme "would get round very quickly", explains Alan Hegan.

"News travels fast, I suppose... overnight everybody seemed to know about stuff," he adds, and and it "seemed that the information was disseminated extremely quickly once it was out there".

But he says he can't point to one source that details about the changes to the scheme "typically came from".

Asked if he ever came across information coming from, as some witnesses have suggested, DUP ministerial advisers - known as spads - he says he "wasn't even aware of what a spad was at that time".

He smiles when he says: "I was more concentrating on pipework and pumps, to be honest!"

When the big financial cracks in the RHI scheme started to appear in the spring of 2015, civil servants at DETI began to draw up changes that would cut the lucrative subsidies on offer.

In the summer of that year, Alan Hegan spoke to DETI official Seamus Hughes (below) on the phone several times about delays in the planned changes to the scheme.

He says the civil servant always seemed to be "open" in their discussions.

Image source, RHI Inquiry

Mr Hegan he was hearing rumours about the changes in industry circles and was contacting Mr Hughes to check if the stories were reliable.

Mr Hegan was aware of changes before they were announced but he didn't see the significance of that "because typically everybody would have knew".

He says some people were better informed than him but once things became known they quickly spread through the industry in a day or two.

The RHI scheme was seen as a "certified, upright government scheme" that had been checked for flaws by those who had designed it, says Alan Hegan.

He was "under the illusion... that there was people a lot more qualified and a lot more intelligent than I was" had set the scheme up.

Image source, RHI Inquiry

He says it wasn't the role of those within the renewable energy industry to "set the policy or to argue with the department".

He would've felt like he was "making a fool out of myself" if he'd told DETI that the cost of the fuel was higher than the subsidy on offer.

"This is what, a £600m, £700m scheme and they don't what price the fuel is? It can't be right."

DETI has accused the renewable energy industry in Northern Ireland of a "conspiracy of silence" about cost of biomass fuel, which was lower than the subsidy on offer from the RHI scheme.

That was the critical flaw that lay at the heart of the scheme's failure.

Mr Hegan is deeply unimpressed by the department's argument that it didn't know how much biomass fuel cost.

Image source, Getty Images

"Google's a wonderful thing if they don't know," he says.

"I'm actually astounded that the... energy department in [DETI] would not know the price of fuel on a scheme that they're rolling out.

"It's the equivalent of saying; 'We don't know what price diesel is, we don't now what price petrol is.'"

Changes to the RHI scheme to make it less lucrative should've been made in January 2015, when sales of biomass boilers in Northern Ireland started to take off, says Alan Hegan.

Image source, Getty Images

"I can't understand why it didn't happen," he adds, saying that those in the renewable industry were expecting DETI to amend the scheme.

He agrees with inquiry QC David Scoffield's suggestion that there was a view among boiler installers that people "should fill your boots as much as you could" before the changes would be made.

Plans to amend the RHI scheme - first outlined in 2013 - to make it less lucrative for smaller boilers were "filed on to a shelf and gathering dust", says Alan Hegan.

Image source, Getty Images

"There was no movement on [the changes], it wasn't coming... there [was] nothing happening," he tells the inquiry.

In his written evidence, he says the Department of Enterprise, Trade and Investment (DETI) knew about the problem but chose to ignore it and he "received no meaningful response" when he raised it.

Alan Hegan says he believes the civil servants and expert consultants who drew up the RHI scheme knew that the subsidies on offer for smaller boilers were far too generous.

Asked by the inquiry chair Sir Patrick Coghlin (below) asks what the witness believes was their "motive" might've been for setting up an "extremely monetary attractive" scheme that "offered you a profit as opposed to an incentive".

Image source, RHI Inquiry

Mr Hegan thinks the plan was to "rapidly encourage" people to sign up in order to help achieve a key target for increasing renewable heat use in Northern Ireland.

"As time went on, that level should've gone down," he says, adding that he "wouldn't have designed the scheme the way it was designed".

He raised issues with the scheme with the Stormont department that had set it up but he says any time he did that "nobody wanted to hear it, nobody cared".

Inquiry panellist Dr Keith MacLean asks about the longevity of biomass boilers because it affects the economics of the scheme - the presumption had been that boilers would run for 20 years.

Alan Hegan says boilers compares boilers with cars, explaining that they need progressively more maintenance as the years pass.

Image source, Getty Images

He says that if a car does 20,000 miles a year it's "going to need maintenance" after three, four or five years and it's "going to need a lot more after 10".

As for the smaller boilers that gave the greatest return from the RHI scheme, he says: "If the car's half the size and it's now doing 40,000 miles a year it's going to need an exponential amount of maintenance".

Not only was the incentive on offer from the RHI scheme too generous for smaller boilers below 99kW but the subsidies that were available for bigger boilers was insufficient, says Alan Hegan.

That further drove people to have multiple smaller boilers installed instead of one bigger unit for their heating need.

"I believe the incentive wasn't enough to justify a larger boiler... where people did examine machines of that size the economics didn't stack up for them," says Mr Hegan.

"The payment that was available [for boilers over 99kW] failed to incentivise installations at that level."

Mr Hegan's company started supplying biomass fuel in the form of woodchip in the early 2000s and fitted a biomass heating system in Cookstown Leisure Centre in County Tyrone in 2007, long before the RHI scheme was introduced.

He was expecting a rise in sales for woodchip fuel and woodchip-fuelled boilers after the scheme opened in Northern Ireland in 2012 but it didn't happen.

He explains that was because the sizes of the boiler that he was marketing - over 100kW - didn't fall into the category that was eligible for the most lucrative subsidy through the scheme.

Instead, smaller boilers of 99kW and below that were fuelled by wood pellets were eligible for the bonanza payments from the scheme.

Instead of people buying one large boiler for their heat requirements, many chose to have multiple smaller boilers installed in order to qualify for the bigger subsidies that were on offer, says Mr Hegan.

"The economics... didn't work for anything above 99kW in Northern Ireland... the mathematics didn't work and no business therefore invested [in larger boilers]."

Alan Hegan settles into the witness chair in the Senate chamber, ready to take questions from the inquiry panel and senior counsel David Scoffield QC.

He's a director at Hegan Biomass Ltd, a renewable heating systems firm based in Dungannon in County Tyrone.

Mr Hegan has submitted two witness statements to the inquiry - you'll find them here, external and here, external.

Image source, RHI Inquiry

Witness statements from numerous other boiler firms have also been published - they're all on the inquiry's website, external.

The inquiry has already heard from two boiler installers - that was back in February, in what now seems like the distant past.

Some of the evidence that day was astonishing and included the claim that one customer was willing to pay whatever it cost to have a biomass boiler flown from Austria to Northern Ireland in order to get it installed before the lucrative RHI scheme closed.

Jayne McCormack
BBC News NI politics reporter

The DUP was under the spotlight at the inquiry last week - leader Arlene Foster, two of her former advisers and ex-adviser and senior backroom figures all faced questions.

Their evidence offered a rare insight into the internal workings of the party.

BBC News NI has picked out five key moments you might have missed - read about them here.

BBC News NI

It is the scandal that sent Northern Ireland's devolved government up in flames and risked leaving taxpayers hundreds of millions of pounds out of pocket.

The RHI debacle has exposed serious flaws in the region's civil service and governance systems.

Image source, Pacemaker

BBC News NI has followed every minute of the inquiry into the scandal since it started last autumn.

Read our review of some of the major revelations that have emerged so far.

BBC News NI

An independent inquiry into the RHI scandal was established in January last year by the then finance minister Máirtín Ó Muilleoir.

He ordered it in the wake of the huge public concern and what was then a major political crisis surrounding the scheme.

The RHI Inquiry began in November last year and Sir Patrick Coghlin (below), a retired Court of Appeal judge, is its chair and has been given full control over how it will operate.

Image source, Pacemaker

It is looking at:

• the design and introduction of the RHI scheme
• the scheme's initial operation, administration, promotion and supervision
• the introduction of revised subsidies and a usage cap for new scheme claimants in autumn 2015
• the scheme's closure in February 2016

For more information on the RHI Inquiry, you can read our handy Q&A.

When the scale of the overspend emerged, public and political concern rocketed.

As the minister in charge of the Stormont department that set up the RHI scheme, the DUP leader Arlene Foster faced calls to resign from her role as Northern Ireland's first minister in December 2016.

Image source, Pacemaker

She resisted, and Sinn Féin's Martin McGuinness then quit as deputy first minister in protest at the DUP's handling of what had by then become a full-blown political crisis.

That move brought about the collapse of the Northern Ireland Executive. Now, well beyond a year-and-a-half on from that, Northern Ireland remains without a devolved administration.

You can find much more detail on the RHI scheme in our need-to-know guide.

The budget of the RHI scheme ran out of control because of critical flaws in the way the initiative was set up.

Claimants could effectively earn more money the more fuel they burned because the subsidies on offer for renewable fuels were far greater than the cost of the fuels themselves.

At one point the estimate for the overspend was set at £700m if permanent cost controls weren't introduced - temporary cuts have since pulled the budget back on track for now.

Whatever the scale of the bill, it will have to be picked up by the Northern Ireland taxpayer.