What installing a pellet stove or boiler actually involves

A competent installer will answer these questions without hesitation, because the answers describe work they do routinely. Hesitation, vagueness or irritation at being asked is itself an answer worth noting.

What to ask before any work starts

• Is the appliance covered by your HETAS registration? HETAS (the Heating Equipment Testing and Approval Scheme) registration is specific to appliance types and fuels, so an installer registered for gas is not automatically registered for biomass. Ask for the registration number and check it yourself on the HETAS online register.
• What size flue liner does this appliance need, and why? The flue liner is the inner sleeve fitted inside a chimney or flue run to match the appliance's exhaust requirements. A proper answer names a diameter and a reason (appliance output, run length, number of bends). Before the survey, you can run the flue height and draught checker yourself: enter the appliance output, the proposed internal diameter and the flue height, and it will flag whether the draught looks adequate for that output class and whether a twin-wall insulated liner is likely needed. It won't replace the installer's own measurements on site, but it gives you a figure to compare against what they tell you. If you want to understand why height and run length change the answer before you even open the checker, the flue height and draught guide walks through what the tool is measuring and where it can get it wrong.
• What clearance distances apply to combustible materials? Hearth size and clearance to timber, plasterboard or furniture are set by the appliance manufacturer's instructions and checked against Building Regulations. An installer should be able to point to the manufacturer's data sheet.
• How will the room be ventilated? Combustion needs a supply of air, and above certain appliance output thresholds a permanent vent is required regardless of how airtight the room already feels. Ask what the appliance's stated output is and whether that triggers a ventilation requirement.
• Will this be self-certified or notified to building control? A HETAS-registered installer can usually self-certify the work under a competent persons scheme, which is faster and cheaper than a local authority building control application, but not every installer or every job qualifies. Ask which route applies and why, and ask for the paperwork that proves it happened.
• What does the quote actually include? Flue liner, hearth, ventilation works, commissioning and certification are separate cost items that can be missing from a headline figure. A written quote should itemise each one.

What the answers tell you

A clear, specific answer to each question is a reasonable sign that the survey has been done properly. A shrug, a verbal assurance with nothing written down, or a quote that omits certification are reasons to ask again before committing.

None of this replaces a competent registered installer's own assessment of your property, and this page does not constitute energy advice. Read the fuller sequence of installation requirements, from flue assessment through to certification, in What Installation Really Involves, and check any installer's current status directly on the HETAS register before agreeing to work.

Fitting a pellet stove or boiler counts as notifiable work under Building Regulations, because it usually means a new flue penetrating a wall or roof, a change to the room's ventilation, and an appliance burning fuel inside an occupied building. The regulation that applies is Approved Document J, which covers combustion appliances and fuel storage. You do not choose whether the work is notifiable. You choose how it gets notified.

Two routes to compliance

There are two ways to satisfy Building Regulations for a solid fuel or biomass appliance, and they lead to the same legal outcome by different paths.

• HETAS self-certification: a HETAS (Heating Equipment Testing and Approval Scheme) registered installer signs off the work themselves and notifies the local authority on your behalf. HETAS is a competent persons scheme recognised under Building Regulations for solid fuel and biomass appliances. You receive a certificate at the end, and no separate council inspection takes place.
• Local authority building control notification: you or your installer notify the council before work starts, and a building control officer inspects the installation, usually after completion. This route applies if your installer is not HETAS-registered, or if you would rather have an independent inspection regardless.

Most homeowners use the HETAS route, because it avoids a separate council fee and a second site visit. It only works if the installer carrying out the work is actually registered for the class of appliance being fitted, which is not the same as being registered at all: registration can be scoped to stoves, boilers, or both.

What each route actually confirms

A HETAS certificate confirms that the specific installation, the flue run, the hearth, the clearances, the ventilation, meets the standard. A building control completion certificate confirms the same technical points through council inspection. Either document is what you produce if you sell the house, claim on insurance after a chimney fire, or need to show a mortgage lender that the heating system is compliant.

Flue height and draught are usually the trickiest part of that check, because the height and diameter decide whether the appliance draws correctly. The flue height and draught guide explains what a surveyor looks for before that visit.

Checking before work starts

Ask which route the installer intends to use, and ask to see the HETAS registration number if that is the route. The number can be checked against the HETAS online register directly. If no certificate of either kind is offered at the end of the job, the work is not compliant regardless of how well the appliance runs.

The flue is usually the part of the job a HETAS surveyor spends the most time on, since its height and diameter decide whether the appliance draws properly. Before that visit, you can run the flue height and draught checker with your appliance's output and the flue dimensions being proposed, which gives a sense of whether the figures are in the right range against BS EN 15287 and whether a twin-wall liner is likely to be needed. It can be wrong for an unusual roof or chimney arrangement, so treat it as a way to arrive at the survey with better questions, not as a substitute for the surveyor's own measurements.

This page does not replace an installer's own survey of your property, and building control requirements can vary by local authority. See Pellets: Quality, Storage and Delivery for what the fuel storage side of Approved Document J involves, or get in touch if you want to talk through what applies to your house.