This is an underserved category and the people in it are frequently sold the wrong thing, because the awkwardness of the conversation gets in the way of the specification.
So here it is plainly.
Where the standard range ends
Most residential stairlifts are rated between 300 and 400 lb. Bruno publishes the Elan SRE-5000 at 300 lb and the Elite SRE-2010 at 400 lb. Harmar publishes the Pinnacle SL600 at 350 lb.
Above that you are in heavy-duty territory, and the options narrow considerably. Harmar publishes the Pinnacle SL600HD at 600 lb.
What changes in the machine
A heavy-duty lift is not a standard lift with a bigger number on the label.
The drive and brake are specified to the load, because both work harder throughout every trip.
The rail and brackets carry more, which means more load into the stair treads and a closer look at the staircase itself at survey.
The seat changes. Harmar pairs the SL600HD with a high-backed extra-wide chair, stationary armrests and a reinforced footrest, which is what makes the rating usable rather than theoretical.
That last point matters most. A lift rated for the weight with a seat somebody cannot sit in comfortably is a lift that will not be used.
Capacity and seat width are two different questions
The commonest specification error in this category.
Ask for the rated capacity, and separately ask for seat width between the arms, seat depth front to back, and seat height from the tread. Then compare those against a chair the person already finds comfortable at home.
Our capacity guide covers the reasoning, and it applies with more force here because the margin is narrower.
The weight conversation
We ask for an actual figure rather than an estimate, and we ask for a current one. It is an awkward question and there is a way to make it less so: give the reason with it.
The model depends on it. Specifying wrong is a safety problem rather than a pricing one, and a lift running near its limit every trip wears faster and fails earlier. Most people answer straightforwardly when the reason is attached, and almost nobody does when it arrives bare.
If the figure sits between two models, go up. The price step between capacities is real and it is far less than replacing a lift early.
What the person carries
The rating covers everything on the lift, not just the person. A bag, a small dog, a laundry basket, a walking frame lifted onto the lap.
Individually none of these matter. Together with somebody close to the rating, they do. Say plainly what will be carried.
Dynamic load
A rating covers somebody sitting still. Getting on heavily, or shifting position mid-travel, produces a brief load above the static weight.
It is a real effect rather than a sales point, and it is another reason to specify with headroom.
Curved staircases at heavy capacity
This is where the options genuinely thin out. Custom flat rail generally supports higher capacities than tube rail, so rail design becomes part of the capacity question rather than a separate one.
If the staircase turns and the capacity requirement is high, expect fewer manufacturers to be able to quote, and expect the lead time and cost of a custom rail. Our rail types guide covers what separates the designs.
When a stairlift is the wrong machine
Worth saying rather than selling around it.
If the person uses a wheelchair and cannot transfer onto a seat, no stairlift at any capacity is the answer. A platform lift carries the chair and its occupant, and both the Bruno VPL-3100 and the Harmar Highlander II are rated at 750 lb.
If the transfer onto a seat is itself unsafe, the same applies. Describe the transfer before anybody names a model.
The rest of the house
Somebody at the upper end of these ratings frequently needs equipment elsewhere rated to match, and standard products routinely are not.
Shower chairs, transfer benches, commodes, rollators and bed rails all carry ratings people do not check, and a plastic frame failing in a wet bathroom is the worst outcome in this trade. Heavy-duty versions exist across all of them.
Ask for the rating on every item rather than assuming, and our seating guide covers what to look at. Heavy-duty equipment ships free from our online shop.
What to ask a supplier
- What is the rated capacity of this exact model and configuration?
- What are the seat dimensions, and is a wider seat available?
- What does this put into the stair treads, and have you assessed them?
- Is this available on a curved rail, and at what capacity?
- What happens to the warranty if the lift is used above its rating?
A supplier who cannot answer all five from the current spec sheet is guessing. All consultations, estimates and scopes of work are free of charge with no pressure or obligation.
What the staircase has to take
A heavier lift puts more load into the treads, so the staircase itself becomes part of the specification rather than a background assumption.
At survey that means a closer look at what the treads are made of, whether there is movement in the flight, whether the stringers are sound, and whether additional fixing points or blocking are needed.
Most timber staircases handle it without difficulty. The ones that need attention are older flights with existing movement, open risers, and stairs that have been altered at some point. None of that is usually fatal to the project and all of it is better known at survey than on install day.
Transfers at higher weights
The riskiest moment with any stairlift is getting on and off, and the margin narrows as weight rises.
Seat height from the tread matters more, because standing from a low seat is harder. A powered swivel matters more, because turning on the seat is harder. Sturdy stationary armrests matter more, because they are what somebody pushes up from.
Harmar pairs the SL600HD with high-backed extra-wide seating, stationary armrests and a reinforced footrest for exactly these reasons. Ask how the specific model addresses each.
Service intervals
A lift working near the upper end of its range earns closer attention. Batteries, drive components and fixings all see more load every trip.
We would service annually as a minimum and would not skip a year. Our maintenance guide covers what a visit should include, and the load test on batteries matters more here than anywhere.
Being treated properly
Worth saying. People in this category are routinely handled badly by this trade: told a standard model will be fine, sold to the limit rather than with headroom, or quietly steered away.
The specification conversation should be matter-of-fact and the equipment should fit the person rather than the person fitting the equipment. If a supplier is awkward about it, that is information about the supplier.
Before you call
Have three things ready: a current weight, the narrowest width of your staircase, and whether the flight turns anywhere including a single wedge-shaped step.
Those three narrow the field before anybody visits, and on a straight flight within the standard range they may produce an answer the same day. Our measuring guide covers taking the dimensions properly.
All consultations, estimates and scopes of work are free of charge with no pressure or obligation, and the equipment that needs no survey ships free from our online shop.