Quite complicated I have found the Polish Rental Tax system. We rang tax offices and still couldn't get a definitive answer.
The missus has the exact info, and I will update but in general this is the way I understand it works.
Firstly as a non-resident you must register to pay tax with the Polish Tax Office in Warsaw.
There are 2 ways of paying tax on Polish rental income.
Outreach Tax: Pay 8% on first €4000 of Rental income. No expenses deductible, including management fee if you are taking for it i.e. you should get the lessee to pay the management fee direct. This rate then goes to something like 20%.
General Tax: Deduct Expenses, including interest and depreciation of 1.5% per year, and pay at 19% up to a certain level. First zl3,000 not taxable. Losses can be carried forward up to 5 years, no more than 50% of losses to be used in 1 year.
On receipt of first income you must declare which option you wish to take.
As I understand it the Polish Tax year is the same as Calendar Year.
Poland and Ireland have a double taxation agreement. I understand this to mean you should calculate the amount of tax you would have to pay as if the property was in Ireland. Deduct the amount already paid to Polish revenue, and pay it over if there is anything due.