They might be full of character and charming features, but period homes can be expensive to keep warm. 

As the energy price cap rises today, they are set to get even more so. 

Data shows that homes with the poorest energy performance certificate ratings could now be paying £591 extra per year on their bills, compared to £221 per year for the average property. 

Older homes are usually the least energy efficient as they are more likely to have solid, uninsulated walls, single-glazed windows and older heating systems.  

A property with an EPC rating of G, the lowest possible, has an average annual energy bill of £5,035 based on today's price cap, compared to £4,444 previously, according to property website Rightmove's monthly energy bill tracker - a £591 rise.

That compares to annual bills of £563 for an A-rated property, a rise of £65 from £498 between April and June. 

A D-rated property is set to see a rise of £284 per year on average.  

Rightmove says that 52 per cent of Britain's homes have an EPC rating of D or below. 

Improving your score involves making your home better insulated or more efficiently heated, for example by replacing the windows, installing wall or roof insulation, replacing the boiler or even getting a heat pump or solar panels. 

While they may be keen to save money on their bills, the upfront cost of these improvements is a major concern for households. Often, they can take years to pay for themselves in cheaper bills.  

Evidence they add value to a property is also mixed. According to recent data from Nationwide, homes with top energy efficiency ratings only attract a modest price premium compared to those which are less green, data has shown.

A property rated A or B on an energy performance certificate is only 1.6 per cent more expensive than a similar home rated D, according to Nationwide.

This is equivalent to around £4,500, based on the average house price in England.  

However, Rightmove said eco credentials were playing an 'increasingly important' role in how people choose their next home. 

Colleen Babcock, Rightmove's property expert, said: 'At the start of the global uncertainty and conflict in Iran in March, we saw a 35 per cent increase in demand for homes with the highest EPC rating compared with the same time last year. 

'It’s a clear sign that when the cost of living becomes more uncertain, energy efficiency moves higher up the priority list.'

Mark Wiggin, Director of Mark Wiggin Estate Agents, added: 'Before 2022, it was rare for buyers to ask about an EPC rating, now it’s one of the most common questions we receive.

'As a result, we're seeing increased demand for modern, energy-efficient homes, while properties with poorer EPC ratings are becoming less desirable. I expect that gap to continue widening, with less efficient homes increasingly underperforming the wider market.'

The energy price cap is going up from £1,641 to £1,862 per year for the typical home, equating to an extra £221 per year or £18.40 a month. 

The figure is based on average energy usage in a three-bed home with two to three people living in it. Households who use more will pay more.  

Those on a fixed tariff aren't governed by the energy price cap, and there are several deals that are cheaper than it. 

> Check the best fixed rate energy deals with Uswitch and This is Money* 

However, before fixing for a year or more, consider whether you think the price cap might decrease again in the future.  

The latest prediction from the independent energy analyst Cornwall Insight puts the price cap at a slightly lower £1,849 from October. 

This is down to easing tensions in the Middle East, which are helping to stabilise wholesale energy markets.

EPC certificates can be obtained by hiring an accredited assessor to visit your home, and cost about £60 to £120. They last for 10 years and must be provided to the buyer when selling your home. 

Some industry experts question whether they are the best way to rate a property's energy efficiency. 

Nathan Emerson, CEO of estate agent membership body Propertymark, said: 'With households facing yet another increase in energy bills, improving the energy efficiency of homes is more important than ever. 

'However, Propertymark has consistently called for reforms to the EPC regime so it provides a more accurate picture of a property’s energy performance and a practical roadmap for improving energy efficiency. 

'Our member agents tell us that while EPCs are an important consideration for buyers and tenants, the current methodology does not always reflect how homes perform in practice, particularly older and traditional properties.'