How to Choose a Window Replacement Contractor

Window replacement is a 30-40-year investment, and 80% of the project’s success depends not on the choice of profile or glazing, but on the quality of installation. Even premium windows costing €1,000/m² can become a source of problems if installed incorrectly: drafts, freezing, condensation, and mold appear within 6-12 months. The price difference between a professional company and a cheap crew is only 10-15%, but correcting installation errors costs €1,500-7,000. In Spain, approximately 40% of windows are installed improperly. We’ll explore how to distinguish a professional contractor from an amateur, what to look for when choosing, and what red flags should alert you.

Why choosing a contractor is critical

Installation is more important than materials

Ratio of influence on the final result:

• Installation quality: 70%
• Profile quality: 15%
• Glass unit quality: 10%
• Hardware: 5%

Typical mistakes made by unprofessional installers:

• Fastening with foam only, without anchors → window will loosen in 1-3 years
• Incorrect leveling → sashes will sag in 6-12 months
• Lack of protection for the installation joint → foam failure in 2-5 years
• Voids in the foam → drafts, freezing
• Using cheap foam → crumbles in 1-2 years

Consequences:

• Heat loss 30-50%
• Need for reinstallation (1500-7000) Euro)
• Loss of comfort for years
• Possible interior damage (condensation, mold)

Criteria for Selecting a Professional Contractor

1. Experience

Minimum: 5 years in business

Window replacement is a specialized job that requires experience. The technology seems simple, but the details are critical.

What to check:

• Year the company was founded
• Number of completed projects (at least 500+ windows)
• Specialization (companies that only make windows perform better than general builders)

Contact Questions:

• How many years have you been in business?
• How many windows do you install per year?
• Do you have your own production facility or do you work with contractors?

Red flags:

• Company has been in business for less than 3 years
• No information on the number of projects
• “We do everything: windows, doors, renovations, plumbing…”

2. Installation Warranty

Minimum: 3 years

The installation warranty is the main indicator of a company’s confidence in its work.

Standard warranties:

• Profile: 10 years (provided by the manufacturer)
• Double-glazed unit: 5 years (provided by the manufacturer)
• Hardware: 3-5 years (provided by the manufacturer)
• Installation: 3-5 years – that’s where the difference lies!

What should be covered by the installation warranty?

• Drafts from the installation joint
• Freezing of window slopes (if installed)
• Condensation on window slopes (if installed)
• Sagging of sashes due to improper installation
• Problems with the window sill/drip
• Destruction of the mounting foam

Questions when contacting:

• What is the installation warranty?
• What exactly is covered by the warranty?
• How quickly do you respond to warranty claims?
• Can you show me the warranty card?

Red flags:

• Installation warranty of 6 months - 1 year (too short)
• No written installation warranty
• Evasive answers: “There is a warranty, but it depends on the situation.”
• “The warranty only covers the windows; we do not guarantee installation.”

Why a short warranty is a bad sign:

Most installation problems appear after 6-18 months:

• Sagging sashes: 6-12 months
• Foam breakdown: 1-2 years
• Drafts: first winter

A company offering a 6-month warranty knows that problems will start later, when the warranty expires.

3. In-house production or direct contracts

Optimal: in-house factory or exclusive dealer

The shorter the chain from production to installation, the better the quality control and delivery times.

Working Options:

Manufacturer with in-house installation (ideal):

• Full quality control
• No intermediaries
• Quick problem resolution
• Usually better warranties

Exclusive dealer of a major manufacturer (good):

• Direct contracts with the factory
• Manufacturer training
• Consistent quality
• Brand commitment

Small company working with several suppliers (average):

• Can offer a variety of options
• But less quality control
• Possible delays

Generalist construction team that orders windows from anywhere (bad):

• No specialization
• No production control
• Often chooses the cheapest option
• Unpredictable quality

Contact Questions:

• Are you a manufacturer or dealer?
• Which factories do you work with?
• Do you have profile manufacturer certificates?
• Can I see your production/warehouse?

Red flags:

• “We’ll order windows from wherever it’s cheaper.”
• No regular suppliers
• Can’t name the profile manufacturer in advance
• They offer “good windows, no matter which one.”

4. Transparent, detailed estimate

Professionals provide a detailed estimate, broken down by item.

What should be included in the estimate:

Window specifications:

• Dimensions of each window
• Profile brand and model
• Double-glazed unit specifications (formula, glass type)
• Hardware type
• Color

Work and materials:

• Dismantling old windows
• Waste removal
• Frame installation (number of anchors)
• Polyurethane foam (type)
• Window sill (material, size)
• Eaves drain
• Sealing (basic or three-layer)
• Slopes (if included – material, technology)
• Hardware adjustment

Prices:

• Price per m² of window
• Price for each additional item
• Total excluding VAT
• VAT 21%
• TOTAL

Questions when contacting:

• Can you provide a detailed estimate?
• What is included in the installation cost?
• Are there any hidden costs?
• What’s not included in the price (slopes, mesh)?

Red flags:

• Only a general figure, no breakdown
• “3,500 euros for all windows” — that’s all
• No materials specifications
• Evasive answers about what’s included
• “We’ll decide later on site”

5. Willingness to explain the technology

Professionals are happy to explain how they will work.

What they should explain:

During measurements:

• How they will measure (three points)
• Why they recommend this particular profile/glass
• How they will secure the frame (anchors, number of points)
• Sealing options (basic or full)
• Are slopes needed and why

Installation technology:

• Dismantling old windows
• Opening preparation (cleaning, priming)
• Frame installation (leveling)
• Fastening (anchors, quantity)
• Sealing (if full, explain the three-layer system)
• Installing the window sill and low tide
• Hanging the sashes
• Adjustment

Technical pause times:*

• Let the primer dry (15-30 minutes)
• Allow the foam to expand for 4-8 hours
• Do not hang the sashes immediately

Questions upon contact:

• How do you attach the frame to the wall?
• How many attachment points do you use?
• How do you protect the mounting foam?
• What is three-layer sealing?
• Why are slopes a separate service?

Good Signs:

• Detailed answers
• Willingness to show diagrams/photos
• Explaining “why”
• Honestly admitting that slopes are essential to protect the foam

Red Flags:

• Evasive answers: “We’ll do it right”
• Can’t explain the technology
• “Don’t worry, we know what to do”
• Take offense at technical questions
• “The foam holds, anchors aren’t necessary”

6. Portfolio and Reviews

Real examples of work and satisfied clients.

What to check:

Portfolio:

• Photos of completed projects
• Different types of properties (apartments, houses, offices)
• Photos of the installation process (not just the finished product)
• Video customer testimonials

Online Reviews:

• Google Maps (minimum 4.0 stars, 20+ reviews)
• Facebook
• Specialized platforms (Habitissimo)

Contact information for previous clients:

• Willingness to provide 2-3 contact details
• Can I call and ask?

Questions to ask during contact:

• Can you show examples of your work?
• Do you have any customer reviews?
• Can you provide 2-3 customer reviews?
• Can I see the property before delivery?

Questions for previous clients:

• Were you satisfied with the result?
• Were there any issues? How were they resolved?
• Installation quality?
• Were there any warranty claims? How did they respond?
• Would you recommend this company?

Red flags:

• No portfolio
• Only perfectly staged photos (clearly from the manufacturer’s website)
• Reviews only on their own website (may be fake)
• Refuse to provide client contact information
• Rating below 4.0 or many negative reviews
• Recent reviews from inactive accounts (cheating)

7. Legal Cleanliness

The company must be officially registered.

What to check:

Registration:

• Availability of a NIF (taxpayer identification number)
• Legal address
• How many years the company has been officially in existence

Insurance:

• Civil Liability Insurance (Civil Liability Insurance)
• Covers damages during work
• Minimum coverage: €300,000-€600,000

Documents:

• Contract with company seal
• Invoice with VAT
• Warranty card with stamp

Contact questions:

• Do you have RC insurance?
• Do you work officially with Factura?
• Do you provide a warranty card with stamp?

Red flags:

• Working without a factura (“cheaper without VAT”)
• No RC insurance
• The company has just been registered
• No legal address
• Cash only, no documents

Risks of working “under the table”:

• No guarantees
• No liability
• If something breaks, they won’t compensate
• You can’t get a tax deduction
• Problems selling an apartment

8. Reasonable deadlines

Professionals give realistic deadlines.

Typical deadlines:

• PVC window production: 2-3 weeks
• Aluminum window production: 3-4 weeks
• Wooden window production: 4-5 weeks
• Installation: 1-3 days depending on volume

Total project duration: 3-8 weeks

Questions when contacting:

• What are the production deadlines?
• When can you install?
• What influences the deadlines?

Good signs:

• Clear, realistic deadlines
• Explanation of what determines the deadlines
• Honest admission that it takes longer during peak season

Red flags:

• Unrealistically fast delivery promises: “We’ll deliver and install tomorrow”
• Vague deadlines: “We’ll do it someday”
• Can’t explain what the deadline depends on
• Constantly postpones the date after the deposit

9. Reasonable pricing policy

The price should be adequate for the market.

Average prices in Spain (2024-2025):

PVC windows:

• Economy (basic profile, plain glass): €250-320/m²
• Standard (good profile, low-e glass): €320-450/m²
• Premium (top profile, special glass): €450-700/m²

Aluminum:

• Standard: €400-600/m²
• Premium with thermal break: €600-900 Euro/m²

Wood:

• Standard: 700-1200 Euro/m²
• Premium: 1200-2000 Euro/m²

The price usually includes:

• Window (profile, glass, fittings)
• Removal of the old window
• Frame installation with anchors
• Foaming
• Basic window sill
• Ebb tide
• Adjustment
• Waste removal

Additionally charged:

• Three-layer sealing + slopes
• Wide window sills (over 25 cm)
• Mosquito nets
• Roller shutters
• High-altitude work (above 3 floors)

Red flags:

Too cheap (30%+ below market):

• They use the cheapest materials
• They skimp on fastenings (only foam)
• They don’t seal
• They skip steps
• They may Disappear after the deposit

Too expensive (50%+ above market):

• Unjustified markup
• Pushing unnecessary options

Unclear pricing policy:

• Price changes after the measurement (significantly higher)
• “Unexpected” surcharges appear
• “This is separate, this is also separate…”

10. Professional behavior

Impression of communication is an important indicator.

Good signs:

At first contact:

• They respond quickly (within 24 hours)
• They ask clarifying questions about the project
• They explain the process
• They offer a free measurement

During measurement:

• They arrive on time
• The measurer is neat, in uniform
• They measure at three points
• They take photos of the openings
• They check the geometry with a level
• They ask the right questions
• They explain the options
• They don’t push Solution

During Communication:

• Professional
• Patiently Answer Questions
• Don’t Get Offended by Inspections
• Willing to Show Documents
• Give You Time to Think

Red Flags:

Pressure:

• “Discount Only Today, More Expensive Tomorrow”
• “We’re in a Queue, Please Decide Quickly”
• “Other Clients Are Waiting, Need an Answer Now”

Unprofessional:

• Arriving Late Without Warning
• Untidy Appearance
• Rude
• Smoking in Your Apartment

Evasiveness:

• Not Answering Technical Questions
• “Don’t Worry, Everything Will Be Fine”
• Get Offended by Warranty Questions
• Not Giving Documents for Review

Dishonesty:

• Promising the Impossible
• Saying Bad Things About All Competitors
• Trying to Scare You (“You’re Doing Really Badly”)
• Pushing Unnecessary Orders

Red Flags: When to Refuse

Critical Red Flags (Refuse immediately)

1. Require a deposit of more than 50%

• Standard: 40-50%
• Red Flag: 70-100%
• Risk: They might disappear with the money

2. Work without documents

• No invoice
• No contract
• No warranty

3. No RC insurance

• If they break something, they won’t reimburse it

4. Warranty less than 1 year or no installation warranty

• They know the work is poor

5. Can’t show examples of their work

• They are either newbies or the work is poor

6. Constantly changing the price

• After the measurements, the price is much higher
• New “mandatory” surcharges appear

7. Aggressive pressure

• They don’t give you time to think
• They threaten or blackmail

Serious Red flags (think about it)

1. Less than 3 years of experience

2. Only positive reviews (suspicious, scam)

3. No regular suppliers

4. They don’t explain the technology

5. Price 30%+ below market

6. They promise unrealistic delivery times

Our advantages

Why choose us

Experience and reputation:

• Over 3 years in the Spanish market and over 15 years in Ukraine and Poland
• 1,000+ successfully completed projects
• 4.8-star rating on Google Maps
• Real reviews from satisfied customers

Installation quality:

• 3-year installation warranty
• We always secure frames with anchors (6-10 points)
• We level with an accuracy of 1 mm
• We offer two options: basic installation or full finishing with a three-layer coating Sealing

Transparency:

• Detailed cost estimate with breakdown
• We honestly explain what is included in the price and what is extra
• No hidden extra charges
• We show examples of our work

Professionalism:

• In-house trained teams
• Professional equipment
• Meet deadlines
• Official paperwork

Materials:

• We work with manufacturers Rehau and Soudal
• Exclusive Rehau dealer
• Only proven materials
• Full quality control

Service:

• Free measurements
• Assistance with obtaining permits (consultations)
• Maintaining cleanliness on site
• Post-installation cleaning
• Post-warranty service

What sets us apart from amateurs

Questions to ask when choosing

Essential questions for any company

1. How ​​many years have you been in business?
2. How ​​many windows do you install per year?
3. What is the installation warranty?
4. How ​​do you attach the frame to the wall? How many mounting points are there?
5. Do you offer triple-layer sealing?
6. What is included in the installation price?
7. What is not included (slopes, mesh)?
8. Do you have RC insurance?
9. Can you show examples of your work?
10. Can you provide contact information for 2-3 clients?
11. What are the manufacturing and installation times?
12. Do you work with Factura?

Questions about materials

1. Which profile do you recommend? Why?
2. What brand of hardware do you use?
3. What kind of foam do you use?
4. Where do you order your double-glazed windows from?

Questions about the process

1. Who will take the measurements?
2. When will I receive a detailed estimate?
3. How ​​is the installation carried out? (technology)
4. How ​​many people are in the team?
5. Do you clean up after yourself?
6. What do I need to prepare?

Questions about the warranty

1. What is covered by the installation warranty?
2. How ​​quickly do you respond to warranty claims?
3. Have you had any warranty claims? How did you decide?

Contractor Selection Checklist

Mandatory criteria (do not order without these):

• Minimum 5 years of experience
• Minimum 3-year installation warranty
• Officially registered (factura, NIF)
• RC insurance available
• Detailed estimate with breakdown
• Can explain installation technology
• Secures frame with anchors (not just foam)

Preferred criteria:

• 4.0+ star rating, 20+ reviews
• In-house production or exclusive dealer
• Portfolio of real projects
• Willingness to provide client contact information
• Professional behavior
• Reasonable price (not too cheap, not too expensive)

Red flags (if any, refuse):

• Advance payment over 50%
• Warranty less than 1 year or none
• Work without documentation
• No RC insurance
• Aggressive pressure
• Can’t explain the technology
• Price 30%+ below market
• ​​[ ] No work examples

Conclusions

Key Takeaways:

1. Installation is more important than materials: 70% of a project’s success depends on the quality of installation, not the brand of the profile.

2. Installation warranty is the main criterion: Minimum 3 years. A short warranty (6 months - 1 year) is a sign of unprofessionalism.

3. Saving on a contractor is expensive: The price difference is 10-15%, and the cost of correcting errors is 1,500-7,000 euros.

4. Check the documentation: RC insurance, invoice, contract, and warranty card are mandatory.

5. Technology is critical: Professionals fasten with anchors, level them, and explain the process. Amateurs rush and skip steps.

6. Don’t choose based solely on price: Consider experience, warranties, reputation, and the initial impression.

7. Red Flags – Seriously: If you see critical red flags, refuse immediately, even if the price is attractive.

Top Tip: Invest time in choosing a contractor. A few hours checking out three or four companies can save you thousands of euros and years of problems. Windows are installed for 30-40 years – your choice of contractor determines whether you’ll be satisfied for all those years or face problems after just the first winter.