Question 1

What is MVHR, and does a house need mechanical ventilation?

Accepted Answer

Mechanical ventilation with heat recovery continuously **extracts stale air and supplies fresh air**, passing them through a heat exchanger so most of the warmth in the outgoing air is transferred to the incoming air without the two mixing.

**Why it exists.** Traditional houses ventilated through draughts — gaps, chimneys, ill-fitting windows. Making buildings airtight for energy efficiency removed that accidental ventilation, and **an airtight house without deliberate ventilation accumulates moisture, carbon dioxide and pollutants.** This is the origin of condensation and mould in otherwise well-insulated homes, and it is why ventilation is regulated alongside insulation rather than separately.

**How MVHR works.** Ducts extract from wet rooms — kitchen, bathroom, utility — and supply to habitable rooms. The heat exchanger typically recovers a large majority of the heat. It runs continuously at a low rate, with boost for cooking and showering.

**When it is genuinely appropriate:** in a **genuinely airtight** building. MVHR in a leaky house is close to pointless, because uncontrolled air movement bypasses the system and you pay running costs for little benefit. **Airtightness is the precondition**, and the two must be designed together.

**What it requires:** duct routes designed in from the start, which is why retrofitting is difficult and expensive; a plant location with access; commissioning to balance the flow rates, **without which it will not perform as specified**; and filter changes, which is the maintenance owners forget.

**The alternatives, in ascending order:**

**Background ventilators (trickle vents) with intermittent extract fans**, the common approach and adequate in a moderately leaky house.

**Continuous mechanical extract ventilation (MEV)**, extracting continuously with air entering through vents — simpler than MVHR, no heat recovery.

**Positive input ventilation (PIV)**, pushing filtered air in from the loft, widely used as a retrofit for condensation problems.

**The general principle:** **build tight, ventilate right.** Airtightness without ventilation causes harm, and ventilation without airtightness wastes heat.

Question 2

What are trickle vents and do I need them?

Accepted Answer

Trickle vents are small, controllable slots in a window frame or head that provide continuous background ventilation without opening the window. Why they exist. Modern homes are sealed far more

Question 3

What causes condensation on the inside of my windows?

Accepted Answer

Condensation forms when moist air meets a surface cold enough to bring it below its dew point. Windows are usually the coldest surface in a room, so they show it first. The moisture is not coming

Question 4

What causes a musty smell in a room?

Accepted Answer

A musty smell is produced by mould and mildew growing somewhere, releasing compounds you can smell before you can see any growth. Air freshener masks it; finding the moisture source is the only real

Question 5

What is a vapour barrier and which side does it go on?

Accepted Answer

A vapour control layer (VCL), often called a vapour barrier, is a membrane restricting water vapour from passing through a building element into the insulation and structure behind it. Why it exists.

Question 6

Why is one room in my house always colder than the others?

Accepted Answer

Because heat loss and heat delivery are not distributed evenly around a house, and one room is usually losing more, receiving less, or both. Working through the possibilities in order saves a lot of

Question 7

How can I improve my home's insulation for better energy efficiency?

Accepted Answer

Improving home insulation enhances energy efficiency, reduces bills, and maintains comfort. Key strategies include assessing current insulation, sealing leaks, and upgrading materials.

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