Heating options for extensions
Looking for an efficient, value-for-money system to ensure your new addition delivers a comfortable living environment all year round? Here’s what you need to know
Whether you’re tackling a rear extension or converting a loft, you’ll have your sights set on creating a cosy, low-bills zone that complements the rest of your home. A key first step is to look at your options for upgrading the thermal performance of the fabric of both the new addition and the existing house. is will minimise any extra heating load (from the added space and/or extra hot water outlets). Most homeowners aim to significantly exceed the minimum efficiency standards set out in Part L1B of the Building Regs. ankfully, it’s pretty easy to achieve this with modern materials and a decent builder. Taking a whole-house approach will not only make your home cheaper to heat, it might even help enable the inclusion of wow-factor features in your new extension. Vast swathes of glazed doors and big rooflights look fantastic, for instance, but they’ll never be as thermally efficient as a well-insulated wall. So look to offset their impact with cost-effective upgrades elsewhere. For example, it could cost as little as a few hundred pounds to top up your loft insulation to modern standards.
Is my boiler big enough?
However well-built your lovely new extension is, the fact is that you’ll be increasing the overall amount of living space that needs to be heated. So, one of the key questions you’ll need to address is whether your existing boiler has enough capacity to cope. As a rule of thumb, if you’ve got a reasonably modern boiler and the extension isn’t huge, then you should be ok. But many projects involve creating a considerable amount of extra floor space – particularly in England, where recent changes to permitted development rights mean you can add an 8m-deep single storey rear extension to a detached house without having to make a formal planning application. So in most cases, heat demand will go up (with the possible exception of ultra high-spec eco retrofits). One part of the equation that’s sometimes neglected at the design stage is domestic hot water (DHW). If your plans involve creating an extra bathroom, for instance, this could be the trigger that indicates a new boiler (and potentially a replacement hot water cylinder) is required to deliver enough hot water at good pressure. So, it’s always a good idea to engage a professional heating engineer to determine your requirements. ey will be able to calculate the exact space heating demand across the house and in individual rooms, along with your household’s DHW requirement, and let you know whether any upgrades are required. One update that’s pretty much always worth doing is insulating any accessible heating and hot water supplies – both the existing pipework and the new runs for the extension.
Switching to renewables
Going green is a big motivation for taking on a major renovation and extension project. If you’re giving the whole place an eco retrofit, this might open the door for tech like air source heat pumps (ASHP). But most home extensions are more modest projects, so switching to renewables may not offer the best value for money. “We supply heat pumps as well as underfloor heating (UFH), and we do
speak to homeowners who want to move away from a traditional boiler, but we always talk to them to understand why they’re keen to do that,” says Jo Snell, senior business development manager at Nu-heat. “An ASHP is brilliant in the right situation, which tends to be a well-insulated property off the mains gas grid where you’re comparing renewable solutions with oil or LPG, but it may not be the best option for extensions.” Heat pumps run at a lower flow temperature than boilers, which may not be compatible with an existing radiator setup. In this situation, you’d need to switch to UFH or oversized radiators throughout the whole house – adding extra cost and disruption. It’s also tricky to bring certain older properties, such as listed buildings, up to the standard of insulation that an ASHP requires. “If you want to keep your existing radiators and it’s difficult to insulate, then we wouldn’t recommend a heat pump,” says Jo.
Can I install underfloor heating in my extension?
Even if you don’t have UFH elsewhere in the house, you can still specify it for an extension. In fact, this is a hugely popular option, largely thanks to the efficient, comfortable, even warmth UFH provides and the fact it frees up wall space for furniture, storage and displaying artwork. “More and more people are choosing underfloor heating for large extension projects, particularly the likes of open-plan kitchen-diners,” says Jo. “is system cuts out the hot and cold spots you experience when there’s a big distance between radiators.” All that’s needed to hook up your extension’s UFH to the main heating network is to split the boiler primaries. “One loop goes to the radiators and one to the underfloor heating,” says Jo. “at way the UFH can call for the heat it needs independently.” e big no-no is combining the two systems in a single room: underfloor heating is designed to run on a long, lowtemperature cycle. So it doesn’t make sense to disrupt this with quickresponse convection heat (except perhaps in a bathroom, where you might want the option of a quick boost of heat from a towel rail). If you are installing UFH, pay close attention to where the existing house and the extension join. “e addition is likely to have a concrete slab with 80-100mm of insulation beneath,” says Jo. “e original building, however, might feature a suspended timber floor or be concrete laid directly over earth.” To get the best results, you need to achieve some consistency, and not just in terms of finished floor levels. “A suspended timber floor will have a heat loss of around 45%, so you’ll need to insulate between the joists,” says Jo. “But an old solid floor will probably only have 6%-10% heat loss, so you don’t have to dig out a sound concrete slab. In fact, there’s a clause in the Building Regs saying exactly that – because the cost of doing it would never be repaid through energy savings.” e recent proliferation of highquality low-profile UFH systems, such as Uponor’s Minitec (www. uponor.co.uk), means that you can run the same setup across both the new and old parts of an openplan zone without losing valuable floor-to-ceiling height. is kind of system, which is likely to cost around £40-£65 per m2 installed, can also make good sense for loft conversions with decent headroom.
What about radiators?
Radiator running costs are a little higher than UFH, and you won’t get the same space-saving and comfort benefits. But they can still be an attractive option. ere’s no doubt radiators are cheaper to fit, for example, with costs as low as £175 per standard radiator (installed) depending on labour rates in your area. Plus, the extension’s emitters can be plumbed into the existing heating loop, rather than requiring their own circuit. ere’s tonnes of design options, too, including modern vertical styles that can fit more neatly into some extensions (between runs of glazed door, for example) than horizontal models. Some of the most impressive contemporary designs on the market could even be considered works of art.
Consider the controls
Whatever setup you choose, it will only operate at the expected efficiency if it’s paired with the right controls. Even a basic programmable thermostat (which you’ll be required to fit as part of a modern system) can achieve savings of 40% compared to an uncontrolled heating setup. e latest smart tech can eke out even better levels of performance, not to mention adding real convenience, especially for extensions and other zoned heating setups.