Could your carpet choice reduce your energy consumption?

Could a better carpet make your home more sustainable by reducing your energy consumption? We find out

Your floor can keep up to 10% of the heat within your home. High-tog carpeting matched to a good underlay is ideal for cold sub-flooring. Brintons Perpetual Textures, woven Axminster, 80/20 wool/nylon; various suppliers.

Choosing a carpet is a complex business. There are thousands of book samples to heave though, a wildly disparate price point between what appears to be exactly the same product, and the added confusion of type, tog, and carpet weight (given in ounces). Visual exhaustion alone can drive off every bit of common sense and creative curiosity. Here’s what you need to know to pile on to a value carpet with good staying power that can also increase the valuable insulation properties of your whole floor.

In terms of look and feel — wool, wool mixes, and synthetics come in loop, twist, and sumptuous, toe-swallowing Saxony varieties. The carpet will be rated for its wear from light to heavy domestic. Choosing the finish of the carpet is largely a matter of taste and budget with a couple of exceptions. A 100% wool Berber will be a loop pile — be warned of pussycat-the-destroyer and that ground-scratching fun-loving dog. Longer piles, despite their sensory joy under bare feet, flatten and show wear sooner than a short, muscular twist or loop. Stick the meat of your thumb into the carpet sample and see how quickly it springs back under pressure. 

The pile weight is a good indicator of the carpet’s staying power under everyday pressure, including the scrubbing of shoes. A carpet density in the area of 40oz-50oz is suggested for living rooms where wear and spillages are inevitable (heavy domestic) while you can dip down to 30oz in the bedroom.

Wool blends in varying percentages with nylon or polypropylene deliver economical and durable flooring, but most hotels opt for 80:20 rations of wool to nylon. Look for a moth-proofed product — standard fare with quality wool blends. Nylon and polypropylene can be as soft as alpaca, and some allow a safe treatment with bleach solutions — always refer to the maker’s instructions.

Get familiar with the specs on the reverse of the samples.

In terms of using the carpet as an insulator, there’s specific detail in the product spec. This comes under what’s termed thermal resistance of the carpet, expressed as a tog-rating (sometimes given as the R rating) and the performance of the unsung hero of the job — underlay. 

The tog is given in a figure between 0.7 and 3.0. R ratings are given in thermal conductivity (in W/mk) from 0.7 to 1.050. The insulating property of the carpeting is cumulative. You can find the figures you need right there on the back of the sample. Don’t panic. We all know tog from the rating on duvets. In carpets, it largely depends on the backing type, the density of the pile and its physical character.

According to the SEAI, 10% of your home’s heat can be lost through the floor. A serious retrofit of batting, membranes, or board insulation to floors in an older building may not be cost-optimal depending on the build type. 

Introducing a denser carpet on good underlay, with a heavier ounce weight and tog, will stop heat escaping through the pile, and will conduct less warmth away from your bare feet (for greater sensory comfort). Replacing any flooring type, there’s a chance for improvement. 

Together with the underlay, carpeting can effectively shore up draughts from breaks in the subfloor. If you look at any sample and just bend it, you’ll find that denser, warmer carpets with a higher tog, reveal the backing less easily than others.

Does a higher tog number or R rating equal a better carpet choice? Not necessarily.

The complete performance of the carpet will be the sum of the tog of the underlay and the tog of the carpet. So, you can improve the thermal performance of a thinner or low-tog-rated carpet, by using a good underlay product with a good tog value. Underlay is a vital physical protectant for your carpet — its shock absorber. It’s the element that gives carpet its essential yield underfoot. Cheap underlay will undermine even luxuriant expensive carpet pile, robbing it of that even wear and material bounce, vital to longevity. 

The higher the footfall — for instance, in a busy hall or family room — the better the underlay should be. Laying carpet upstairs and on stairs, your underlay will muffle some of the nerve-shredding resonant noise of thundering kids. Just like you should replace the divan with the mattress of your bed, old underlay is structurally compromised by years of use, and should go out with any old carpet.

An underlay with a good tog matched to a carpet with a reasonable tog can smugly address a cold floor even with a budget buy. It should be at least as thick as the carpet it’s protecting; 10mm-11mm underlay will give any carpet that hotel plush feel underfoot. For older homes, a snug underlay can seal up gaps in boards and around conduits, for a perceptive improvement in comfort levels. Address gaps you find in the sub-flooring with flexible sealant before laying carpeting as fully as you can.

A high tog value is not the full story. Using underfloor heating (UFH) we need heat to transmit through the flooring materials into the airspace. The screed or sub-floor is the heat emitter — just imagine it as one great big radiator. 

You absolutely can have carpeting over UFH, but the tog of the carpet, its backing type and the underlay chosen cannot insulate the floor to the point your UFH is struggling and slowing the heat transfer. The Carpet Foundation and the Underfloor Heating Manufacturing Association (UK) recommend a combined tog rating of the carpet and any underlay of no more than 2.5. 

The backing of the carpet should also be a woven style (hessian for instance) rather than a continuous, smothering layer of dense material like rubber that will block heat from rising. Your supplier will be able to point you towards UFH-suitable carpeting (flagged on the book) and match it to a dedicated underlay.

The tog rating can quickly breach 2.5 with an underlay, but industry research has shown it is possible to take a full tog from the complete carpet/underlay number as a working tog rate for the complete carpeting layers for UFH. Your heating installer for the UFH should be the ultimate judge. Where carpeting does shine in terms of UFH, is that it will hold heat for slightly longer than tile, making the flooring exquisitely cosy.

In terms of materials for underlay — what’s on offer? Carpeting and underlay cannot be currently recycled in Ireland, so look for products in recycled materials wherever possible. Polyurethane (PU) is a highly affordable, versatile underlay. 

Its variety in thickness and density has made it a very popular choice that will suit different carpets and situations. It is made from trims from PU blocks, used for other things like making soft furnishings so it does use up waste materials; prices from €5.50 per square metre. Felt is a classic choice for protecting wool carpeting and comes in 100% recycled materials from around €7 per square metre. 

Felt/crumb rubber (combination underlay) offers the high durability and insulation values of rubber with the protective give of a traditional woollen felt. Rubber and hybrids utilise old vehicle tyres (around one car tyre for every square metre) making them a premium, eco-friendly choice for hard-working halls and corridors; prices from €10 per square metre depending on brand. 

100% sheep wool insulation is earth-friendly, with a high tog value of 3.5-plus. If wool does end up in landfill it is at least biodegradable; one m wide, ten m long, ten sq m per roll, €125.90 (€12.60 per square metre), sheepwoolinsulation.com.