The DUP leader Arlene Foster has said none of the businesses getting RHI subsidy are on a party register of donors.
She also said a decision by her former special adviser Andrew Crawford to pass confidential government plans for cost controls to family members may well be a breach of several codes of ethics.
The information is in her witness statement to the RHI inquiry.
She is due to give evidence on Thursday.
Mrs Foster said the party kept a central register of any donor that gave it more than £500.
"From those records, no person or business who has received or is receiving subsidies is a donor to the DUP," the statement said.
It added that she did not believe two big companies with an interest in the RHI scheme were party donors.
She said she did not believe that poultry giant Moypark gave money to the DUP, nor did she hold the view that Balcas, a Fermanagh based wood pellet manufacturer, had any links to her party.
In her statement, Arlene Foster also said she relied on her civil servants and her special adviser (Spad) Andrew Crawford to advise her on the technical aspects of schemes.
She said she had no recollection of being warned of the dangers of proceeding with RHI in the absence of cost controls.
If she had been, those warnings had been downplayed, she said.
The cost controls on the scheme were needed to deal with increasing pressure on the budget as the number of applications began to steadily rise.
Senior civil servant Fiona Hepper has already given evidence to the inquiry that she clearly advised the minister of the risk which had been pointed out by scheme administrator, Ofgem.
There are no records of her meeting with Mrs Foster.
Mrs Foster was also asked about Andrew Crawford's decision to forward confidential government plans for cost controls to two family members months before they were made public.
In her statement, Mrs Foster said she had no idea why he had done it, adding that it had been "clearly inappropriate" and "may well be a breach of the various codes referred to".
Those codes included the code of conduct for special advisers, the Northern Ireland Civil Service code of ethics and a code covering conduct of those in public life.
In his witness statement to the inquiry, Mr Crawford accepted it was "inappropriate" to have shared those plans with family members.
Mr Crawford resigned from his role as an adviser to Arlene Foster in January 2017, days after he was accused of trying to keep the flawed green energy scheme open as it ran out of budgetary control.
On Wednesday, he appeared before the RHI inquiry and denied the accusation.