Retirement Plans for Plumbing and HVAC Business Owners: Solo 401(k), Safe Harbor, and Union Considerations
Plumbing and HVAC business owners earning $100,000-$250,000+ in net profit can shelter $40,000-$72,000 per year in retirement plans. The plan choice depends on the business structure: a solo operator or owner-and-spouse team uses the Solo 401(k); a company with journeymen, apprentices, and office staff needs a plan that includes those employees. Union plumbing and HVAC companies have an additional layer: union members typically participate in a multi-employer pension plan through the union, and the employer’s contribution to that plan is a separate, mandatory expense.
A solo plumber or HVAC technician (no employees other than a spouse) should use the Solo 401(k): $24,500 employee deferral (2026) plus 20% of net self-employment income (or 25% of W-2 salary for S-Corp owners) as an employer contribution, up to $72,000 combined. A company with non-union employees uses a Safe Harbor 401(k) with a 1-year, 1,000-hour eligibility requirement: this allows the owner to defer $24,500 plus employer contributions while limiting the cost of covering employees (apprentices who leave within a year never become eligible). Union companies contribute to the union pension fund on behalf of union members (typically $5-$15 per hour worked, negotiated in the collective bargaining agreement) and may offer a separate retirement plan for non-union employees (office staff, non-union technicians). The union pension contribution is deductible as a labor cost, not a retirement plan contribution, and does not limit the owner’s ability to contribute to their own plan.
How does the Solo 401(k) work for a solo plumber?
What about companies with apprentices?
Plumbing and HVAC companies that train apprentices face a common retirement plan challenge: apprentices often cycle through the business during their 4-5 year training period, and turnover is significant in the first year. The 1-year, 1,000-hour eligibility requirement for a Safe Harbor 401(k) excludes apprentices who leave within their first year.
For apprentices who stay and become eligible, the Safe Harbor 401(k) requires a 3% non-elective contribution on their compensation. An apprentice earning $35,000/year receives a $1,050 employer contribution. For a company with 4 eligible apprentices, the annual cost is $4,200, which is modest compared to the owner’s $24,500+ in personal contributions.
What about union pension obligations?
Union plumbing and HVAC companies contribute to multi-employer pension plans (such as the UA National Pension Plan for United Association plumbers and pipefitters). The contribution rate is set in the collective bargaining agreement, typically $5-$15 per hour worked by union members.
These contributions are deductible as a cost of labor (they are part of the negotiated compensation package). They are not “retirement plan contributions” in the sense of the employer’s own plan. The owner can still maintain a separate retirement plan (Solo 401(k) if no other employees, or Safe Harbor 401(k) for non-union staff) without any conflict with the union pension obligation.
Related guides:
- Plumbing Hvac Entity Structure Scorp
- Plumbing Hvac Equipment Vehicles Section 179
- Plumbing Hvac Estimated Taxes Seasonal
- Plumbing Hvac Insurance Bonding
- Plumbing Hvac Worker Classification Apprentices
When does a plumbing or HVAC owner have to fund the plan?
A solo plumber with a Solo 401(k) elects employee deferrals by December 31 and can deposit them, with the employer contribution, by the return due date including extensions. For a 2025 sole proprietor that’s October 15, 2026 with Form 4868. An S corporation shop follows its own return, due March 16, 2026 for 2025 unless extended.
Once journeymen and apprentices are in a Safe Harbor 401(k), their deferrals run on a much shorter clock. Money withheld from pay has to go in as soon as it can reasonably be separated from company funds, with the 15th business day of the next month as the outer limit. A plan with fewer than 100 participants has a safe harbor for deposits made within 7 business days.
- A solo owner who missed December can adopt a Solo 401(k) after year-end and make 2025 deferrals by April 15, 2026, but only as an unincorporated business with no employees, spouse included.
Can I set up a retirement plan that covers my apprentices and journeymen?
Yes. If you have W-2 employees, your retirement plan must generally include them once they meet eligibility requirements (typically age 21 and one year of service). A SIMPLE IRA is the easiest option for trade businesses with fewer than 100 employees: setup is straightforward, administration is minimal, and the employer match (2-3%) is affordable. If your apprentices are union members, their retirement benefits are likely handled through the union pension fund, and you contribute to that fund based on hours worked (typically reported on the certified payroll). Union workers would not be in your company’s separate plan. For non-union shops, a 401(k) with a safe harbor match lets you as the owner maximize contributions ($24,500 employee deferral for 2026 plus employer profit sharing) without worrying about discrimination testing. The employer contribution for all eligible employees is a deductible business expense.
Start with a Diagnostic: a CPA licensed in the US and Canada reads your file and tells you in writing what's wrong and how to fix it, three to four business days after you finish the questions. The report is $250. If you hire us for any work after that, you get the $250 back as a discount on that work. Or send us your return or your letter and get a fixed price, free.
One or two plain-English guides a week on US-Canada tax. No spam, unsubscribe anytime.
Done. The next guide will land in your inbox.
Yarik Yarosh, CPA. "Retirement Plans for Plumbing and HVAC Business Owners: Solo 401(k), Safe Harbor, and Union Considerations." Blue Cloud CPA, September 5, 2026, updated September 23, 2026. https://bluecloudcpa.com/guides/plumbing-hvac-retirement-plans
This guide is general information, not tax advice for your specific situation. Which points apply, and how, depends on your facts.