Heating a greenhouse is one of the most misunderstood parts of UK gardening. Some growers assume heat is essential, while others avoid it entirely, worried about costs or safety.
The truth sits somewhere in the middle.
This guide explains how to heat a greenhouse in the UK, when heating is genuinely useful, and when it’s unnecessary. It’s designed to help you make calm, informed decisions — before you worry about heaters, running costs, or equipment.
If you’re completely new to greenhouse growing, it also helps to understand the basics of structure, ventilation, and seasonal use first — something we cover in How to Use a Greenhouse (or Polytunnel).
🌱 How to Heat a Greenhouse: Do You Actually Need Heating in the UK?
In most cases, no — not all greenhouses need heating.
A greenhouse already provides several benefits without any heater at all:
- Protection from wind and rain
- Higher daytime temperatures
- Reduced frost exposure
- Earlier spring starts and later autumn harvests
For many UK gardeners growing hardy vegetables, salads, or overwintering plants, this passive protection is enough — especially when paired with the right greenhouse design and placement, which we explore more broadly in the Greenhouses and Polytunnels Resource Hub.
Heating becomes relevant when:
- You want to prevent frost damage, not just slow growth
- You’re growing tender plants (chillies, tomatoes, citrus)
- You want year-round or early-season production
- Your greenhouse is small, thin-glazed, or exposed
Think of heating as a tool, not a requirement.
❄️ When Heating Is Worth It — and When It Isn’t
Heating is worth considering if:
- Night temperatures regularly drop below 0°C
- You’re starting seeds in late winter
- You grow frost-sensitive plants
- You want reliable growth, not just survival
Heating is often unnecessary if:
- You only overwinter hardy plants
- You grow spring–summer crops only
- Your goal is frost avoidance, not warmth
- You use insulation and thermal mass well
Many UK gardeners overheat when all they really need is frost protection — particularly in smaller structures such as mini greenhouses or compact lean-to designs.
🔌 Electric Greenhouse Heaters (Controlled & Reliable)
Electric heaters are the most common greenhouse heater option in the UK, particularly for home gardeners.
How they work
They use mains electricity and often include:
- Thermostats
- Fan-assisted heat circulation
- Frost-protection modes
Pros
- Precise temperature control
- Clean (no fumes or moisture)
- Low fire risk when installed correctly
- Ideal for seed starting and tender plants
Cons
- Running costs can add up
- Requires safe outdoor electrics
- Less suitable for off-grid setups
Electric greenhouse heaters are best used to maintain minimum temperatures, not to create tropical conditions — especially in smaller greenhouses where heat builds quickly.
☀️ Solar Greenhouse Heaters (Limited but Useful)
A solar greenhouse heater sounds ideal, but expectations matter — particularly in the UK climate.
What solar can realistically do in the UK
- Provide daytime warmth
- Power small fans or heat-storage systems
- Support passive heating setups
What it usually can’t do
- Provide reliable overnight heat in winter
- Prevent frost on its own
Most solar-based greenhouse heating works best when combined with:
- Thermal mass (water barrels, stone)
- Good insulation
- Backup frost protection
Solar is best viewed as a support system, not a standalone solution.
🔥 Paraffin Greenhouse Heaters (Traditional but Tricky)
The paraffin greenhouse heater has been used in UK gardens for decades and still appears in many traditional setups.
Pros
- No electricity required
- Relatively cheap to buy
- Produces some CO₂ as a by-product
Cons
- Ongoing fuel costs
- Fire risk if poorly placed
- Adds moisture (can increase mould risk)
- Ventilation is essential
Paraffin heaters can be effective for basic frost protection, but they demand care, monitoring, and good airflow — particularly in enclosed or smaller greenhouses.
🧱 Passive Greenhouse Heating Methods (Often Overlooked)
Passive heating methods often deliver the biggest gains for the lowest cost — and can significantly reduce the need for active heating.
Thermal mass
- Water barrels
- Stone slabs
- Brick or masonry walls
These absorb heat during the day and release it slowly overnight.
Insulation
- Bubble wrap glazing
- Insulated north walls
- Draught sealing around doors and vents
Fleece and covers
- Protect plants directly
- Reduce overnight heat loss
- Very low cost and flexible
For many UK growers, passive methods combined with frost protection outperform heaters alone — particularly in polytunnels and unheated greenhouses.
💷 Running Costs & Efficiency (What Matters Most)
Exact costs vary widely, but efficiency depends far more on heat retention than heat generation.
Key factors that reduce running costs:
- Insulation before heating
- Smaller heated zones
- Thermostats and timers
- Avoiding unnecessary temperature targets
A lightly heated, well-insulated greenhouse often costs less to run than a poorly insulated one with a powerful heater.
⚠️ Safety Considerations You Shouldn’t Ignore
Electric heaters
- Use outdoor-rated sockets and RCD protection
- Keep cables off wet ground
- Avoid cheap extension leads
Paraffin heaters
- Maintain clearance from plants and plastics
- Ventilate regularly
- Never refuel when hot
General safety
- Avoid open flames near dry materials
- Keep heaters stable and level
- Don’t heat more than necessary
Safety always matters more than speed or plant growth.
🌡️ What Temperatures Do Common Crops Actually Need?
Many beginners aim too high.
Approximate minimum temperatures:
- Hardy salads: 0–5°C
- Brassicas: 0°C
- Tomatoes & chillies: 10°C+
- Seedlings: 12–18°C
- Citrus & tender plants: 5–10°C
Often, the goal is preventing damage, not encouraging rapid growth.
🚫 Common Beginner Mistakes with Greenhouse Heating
- Heating without insulating first
- Trying to grow summer crops in mid-winter
- Overestimating solar heating capability
- Ignoring humidity build-up
- Heating the entire greenhouse instead of zones
Understanding why you’re heating is more important than how.
🌿 Final Thoughts: Heat with Purpose, Not Habit
In the UK, greenhouse heating works best when it’s:
- Targeted
- Minimal
- Combined with passive methods
Many successful growers use little or no heating, relying instead on insulation, timing, and plant choice.
Once you understand these principles, you’ll be in the perfect position to decide whether active heating is worth it — and, if so, which type makes sense for your setup.
For further guidance grounded in UK growing conditions, the Royal Horticultural Society also offers practical advice on heating greenhouses efficiently
❓ Greenhouse Heating FAQs
How to heat a greenhouse in the UK without spending a lot on energy?
The most effective way to heat a greenhouse cheaply in the UK is to reduce heat loss before adding any heater. Insulation, bubble wrap glazing, fleece, and thermal mass (such as water barrels) often make a bigger difference than active heating. Many gardeners find that once insulation is improved, only minimal heating — or none at all — is required.
How to heat a greenhouse without electricity?
If you want to know how to heat a greenhouse without electricity, your options are limited but still workable. Paraffin heaters can provide basic frost protection, while passive methods like thermal mass, insulation, and plant covers help retain daytime warmth. In the UK climate, these approaches are usually aimed at preventing frost rather than maintaining warm growing temperatures.
How to heat a greenhouse in winter without overheating plants?
When learning how to heat a greenhouse in winter, the key is control. The goal is usually to prevent frost, not to create constant warmth. Using thermostats, heating only at night, and combining gentle heat with insulation helps avoid temperature spikes that can stress plants or increase humidity-related problems.
How warm does a greenhouse actually need to be in winter?
Understanding how to heat a greenhouse properly starts with knowing plant requirements. Many hardy crops only need temperatures kept just above freezing, while tender plants may need 5–10°C or more. Heating beyond what your plants actually need wastes energy and can encourage weak, leggy growth.
Is it better to heat the whole greenhouse or just certain areas?
For most home growers, the most efficient approach to how to heat a greenhouse is zoning. Heating a small area — such as a seed tray bench or propagation zone — uses far less energy than heating the entire structure. This is especially effective in small greenhouses and lean-to designs.
Is heating always necessary, or can a greenhouse be used unheated?
A common misconception when researching how to heat a greenhouse is that heating is always required. In reality, many UK gardeners successfully grow crops year-round in unheated greenhouses by choosing suitable plants, improving insulation, and adjusting sowing times. Heating is a tool, not a requirement.
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