Reviewed by the Quel Tap product team. Last updated: October 2026.
Boiler capacity decides how a boiling water tap feels to live with. Every other choice, from finish to shape to controls, is about the tap you can see. The boiler decides whether the tap keeps up with your kitchen on a Sunday morning, when three people want tea and a pan is waiting to be filled.
This guide explains what the 2.4 litre and 4 litre figures mean, how to match a size to your household, and what to check in the cupboard before you order. Boiler size, sometimes searched for as tank size, is also the specification most often glossed over, so the figures are set out plainly.
Quick answer
For most one- and two-person households, the 2.4 litre boiler (up to 54 cups an hour) is a comfortable fit. The 4 litre boiler (up to 92 cups an hour) suits larger households, those who regularly entertain and keen cooks. Both heat filtered water to up to 98°C, so the choice is about how much you can draw in a busy hour, not how hot the water is. Full boiler options are shown on each product page.
What boiler capacity actually tells you
Boiler size is quoted two different ways, and the difference matters.
Capacity is how much boiling water the boiler holds and can dispense in one go. Output per hour is how much it can deliver over a full hour, reheating continuously as it goes. A boiler doesn’t empty and then stop; it refills and reheats as you draw from it. Capacity tells you about your busiest thirty seconds. Output tells you about your busiest hour.
| At a glance | 2.4 litre boiler | 4 litre boiler |
|---|---|---|
| Held ready at any moment | 2.4 litres, roughly 10 cups | 4 litres, roughly 16 cups |
| Output per hour | Approximately 13 litres | Approximately 22 litres |
| Cups per hour | Up to 54 | Up to 92 |
| Temperature | Filtered water at up to 98°C | Filtered water at up to 98°C |
| Heat-up from cold | Approximately 8 minutes | Approximately 12 minutes |
| Size (height x width x depth) | 262 x 196 x 196mm | 272 x 200 x 289mm |
| Comfortable with | Everyday household use, drinks and cooking through the day | Back-to-back demand, larger households and regular entertaining |
Both sizes hold water at the same temperature, so this isn’t a decision about how hot the water is or how quickly it arrives. It’s about how much you can draw before the boiler needs a moment to catch up. Treat the cup figures as a comfortable guide rather than a hard limit.
Matching capacity to your household
Household size gives you a rough answer, and how the water gets used through the day sharpens it. The average UK household has 2.36 residents, according to the Office for National Statistics, so for many homes the 2.4 litre boiler is ample.
| Household | Typical pattern | Generally suits |
|---|---|---|
| One or two people | A few drinks through the day, cooking most evenings | 2.4 litre |
| Family of three or four | Morning drinks close together, pans filled at teatime | 2.4 litres for many, 4 litres if mornings are busy |
| Five or more | Several people wanting drinks in the same ten minutes | 4 litre |
| Working from home | Steady demand all day rather than concentrated peaks | 2.4 litre |
| Regular entertaining | Rounds of tea and coffee for six or more at once | 4 litre |
| Keen cooks | Pans, stock and blanching alongside everyday drinks | 4 litre |
Why usage patterns matter more than numbers
Two households of the same size can need different boilers, and the reason is timing.
A house where everyone drifts into the kitchen at different times spreads its demand out. The boiler reheats between each cup and never gets close to running low, so a 2.4 litre is comfortable even with several people in the house.
A house where everyone leaves at the same time concentrates its demand. Three or four cups in the same few minutes, a flask filled, a pan put on, all before eight o’clock. That’s the pattern a 4-litre boiler is built for.
So the useful question isn’t how many people live in your home. It’s how many want boiling water within the same ten minutes, and whether that happens most days or only occasionally. If you’re on the line between the two sizes, think about your busiest morning of the week rather than your average one.
Cooking tips the balance too, more than people expect. Filling a large pan takes a good share of a smaller boiler in one go, so if you cook pasta, rice or vegetables several times a week, that’s a genuine argument for the larger size even in a smaller household.
Boiling water taps for households in transition
Boiler capacity is easiest to judge against the way your household runs now. It helps to picture how it might run in a year or two as well.
Multi-generational homes
Parents, grandparents and adult children under one roof means more people wanting boiling water, often in overlapping morning routines. The ONS reports that 7.2 million young adults aged 15 to 34 lived with their parents in 2025. Three or four people making drinks within the same half hour is the routine the 4 litre boiler handles comfortably, so it’s the size to choose where the kitchen is genuinely shared rather than just busy.
Households going through a change
Children leaving for university, adult children moving back after time away for study or travel, a household that’s growing or shrinking. Each shifts how much boiling water a kitchen gets through, and not always in the direction you’d expect. If you’re planning for the next few years rather than this one, choose the size that suits where the household is heading. A 2.4 litre boiler suits a quieter kitchen, and the extra headroom of the 4 litre suits a house filling back up.
Renovation for a more convenient kitchen
If a boiling water tap is part of a wider kitchen upgrade, the boiler is easiest to plan while the cupboards are still being designed. The 4 litre boiler is deeper than the 2.4 litre (289mm against 196mm), so allow for it at the design stage. If the tap is also replacing the filter jug and the sparkling water machine, the chilled and sparkling models need room for a chiller as well, so cupboard space matters as much as boiler size.
Where the boiler sits
Both sizes are designed to live in the cupboard under the sink alongside the filter housing, and a standard 600mm cupboard is generally sufficient for the boiler and filter housing. The larger boiler takes up more room, particularly in depth, so check your measurements against it before deciding. Dimensions for each model are listed on the product specifications pages.
Both connect to your cold mains supply and a standard 13 amp socket in the cupboard. The power cable is 1.5 metres long, so the socket should be within about a metre of the boiler. Both feed from the same filtered supply line, so the filtered water and standard hot and cold arrangement is identical whichever size you choose.
Changing boiler size later
Of all the choices you make when buying a boiling water tap, boiler capacity is among the easiest to revisit.
Quel Tap boilers are sold as separate products and listed as compatible with all Quel Tap models, so if a household grows, or working patterns change, speak to the UK team about moving up a size without replacing the tap. The tap you chose on looks stays exactly as it is. Standard prices start from £399 for the 2.4 litre boiler and £499 for the 4 litre, inc. VAT, and promotions may apply from time to time, so check the boilers page for current prices.
That takes some pressure off the decision. If you’re genuinely torn, the 2.4 litre boiler is a comfortable starting point for most households, and the larger one is there if your kitchen turns out to be busier than you thought.
Choosing your size
Start with your busiest ten minutes of the week. If that involves two or three drinks and the odd pan, a 2.4 litre boiler will handle it comfortably. If it involves a queue at the kettle and cooking at the same time, choose the 4 litre and enjoy not thinking about it again.
Everything else about the tap, including the finish, the shape, the controls and the pull-out spray, stays open to you either way. Boiler capacity is a practical decision made underneath the worktop, and the tap on top is still yours to choose freely.
Ready to choose your size?
Boiler options are shown on each product page, so you can compare capacity and tap together. Browse the full boiling water tap range, or talk it through with the UK team if you’d like a view on which size suits your household.
Frequently Asked Questions (FAQs)
Does boiler size affect how hot the water is?
No. Both the 2.4 litre and 4 litre boilers hold filtered water at up to 98°C, so the water arrives at the same temperature either way. Capacity only affects how much you can draw in succession before the boiler reheats.
How many cups of boiling water can each boiler deliver?
The 2.4 litre boiler delivers approximately 13 litres an hour, which is up to 54 cups. The 4 litre boiler delivers approximately 22 litres an hour, which is up to 92 cups. The boiler refills and reheats automatically after each use, so those figures describe a full hour of back-to-back drinks rather than a single draw.
Does boiler size change anything about installation?
The process is the same for both. The only practical difference is the space the unit occupies in the cupboard: the 4 litre boiler measures 272 x 200 x 289mm against 262 x 196 x 196mm for the 2.4 litre. Confirm your measurements against the larger boiler if that’s the one you’re leaning towards.
Does a larger boiler take longer to heat up from cold?
Yes, a little. The product pages give approximately 8 minutes from cold for the 2.4 litre boiler and approximately 12 minutes for the 4 litre. This only applies when the tap is first installed or switched back on after being off for a while. In everyday use, the boiler reheats as you draw from it, so you won’t notice a difference between the two sizes.
Can I change my boiler size later?
Quel Tap boilers are sold as separate products and listed as compatible with all Quel Tap models, so moving up a size doesn’t mean replacing the tap. Speak to the UK team first, who can confirm what suits your model and your cupboard.