A leaking boiler, decades-old radiant floor tubing and a separate water heater made this more than a simple equipment swap. We pressure tested the radiant slab before installing a 95% AFUE Lochinvar Noble combi boiler.
This Chelmsford homeowner called Pespisa with a gas boiler that was leaking and nearing the end of its service life. Replacing the boiler itself was straightforward. The heating system connected to it needed more attention.
Part of the home is heated by radiant tubing buried inside an older concrete slab. The rest uses hydronic baseboard heat. Before connecting a new boiler to the existing radiant system, we needed to know whether the buried tubing could still hold pressure.
We isolated the radiant loops and pressure tested them at 25 PSI for 24 hours. The system held pressure, giving us the information we needed to move ahead with the new boiler installation.
We then installed a wall-mounted Lochinvar Noble natural gas combi boiler that provides both space heating and domestic hot water.
The Challenge
A Leaking Boiler and Decades-Old Radiant Floor Heat
The existing boiler was not the only thing we needed to evaluate.
When we arrived, the home had:
- A leaking natural gas boiler nearing the end of its service life
- Radiant heating tubing buried in an older concrete slab
- Baseboard heating serving the rest of the house
- A separate water heater that would also need replacement
- Existing chimney venting that needed to be adapted for the new condensing boiler
Replacing the boiler without first checking the radiant loops would have left an important question unanswered.
Before connecting new equipment to decades-old tubing buried in concrete, we needed to confirm that the radiant system could still hold pressure.
Our Boiler Replacement Solution
A Leaking Boiler and Decades-Old Radiant Floor Heat
The existing boiler was not the only thing we needed to evaluate.
When we arrived, the home had:
- A leaking natural gas boiler nearing the end of its service life
- Radiant heating tubing buried in an older concrete slab
- Baseboard heating serving the rest of the house
- A separate water heater that would also need replacement
- Existing chimney venting that needed to be adapted for the new condensing boiler
Replacing the boiler without first checking the radiant loops would have left an important question unanswered.
Before connecting new equipment to decades-old tubing buried in concrete, we needed to confirm that the radiant system could still hold pressure.
Pressure Testing the Radiant Slab Before Installation
We divided the project into two visits.
The first visit happened before the new equipment was installed.
We:
- Isolated the in-slab radiant loops from the rest of the heating system
- Pressurized the radiant tubing to 25 PSI
- Left the loops under test for 24 hours
- Returned and confirmed that there had been no pressure loss
The radiant slab passed the test, so we could move forward knowing the buried heating loops were holding pressure at the time of testing.
Installing the Lochinvar Noble Combi Boiler
On the second visit, we removed the existing boiler and installed a Lochinvar Noble NKC150N natural gas combi boiler.
The installation included:
- Lochinvar Noble NKC150N wall-mounted combi boiler
- 150,000 BTU/hr input
- 95% AFUE
- Space heating and domestic hot-water production
- New gas line to the boiler
- New primary-loop piping
- New expansion tank
- New Caleffi fill valve with backflow preventer
- High-efficiency ECM circulators
- New section of baseboard in the boiler room
- Updated combustion-air and flue venting
- Permits and inspection
The NKC150N is a 95% AFUE natural-gas combi boiler designed to provide both space heating and domestic hot water.
Radiant Floor and Baseboard Heating From One System
This home uses two types of hydronic heating.
Part of the house is heated through tubing embedded in the concrete slab, while other areas use baseboard heat.
Rather than replacing either distribution system, we rebuilt the primary-loop piping so the new boiler could continue serving both.
The system also received new circulators, an expansion tank, fill and backflow protection, and updated controls.
Outdoor Reset for the Radiant Heating System
The Lochinvar boiler uses outdoor reset control to adjust the heating-water temperature as outdoor conditions change.
When the weather is milder, the boiler can operate at a lower target water temperature rather than supplying the same temperature throughout the entire heating season.
This is particularly useful in a home with radiant floor heating because a concrete slab responds more slowly to changes in temperature than conventional baseboard.
Updated Boiler Venting
The new condensing boiler required a different venting arrangement from the older boiler.
Pespisa installed a dedicated combustion-air intake and a Centrotherm InnoFlue system using the existing chimney route.
The venting was completed as part of the permitted installation and inspection.
Why a Combi Boiler Was the Right Fit
A combi boiler is not the right answer for every home. For this Chelmsford project, several factors made it a practical fit.
One Appliance for Heating and Hot Water
The home’s separate water heater was also approaching replacement.
The Lochinvar Noble allows one wall-mounted appliance to provide both space heating and domestic hot water. Removing the separate storage water heater also gave the homeowner more usable floor space in the mechanical room.
The Existing Radiant and Baseboard Heat Could Stay
The radiant slab passed its pressure test, and the home’s baseboard heating could remain in service.
Instead of replacing the existing heat distribution, we rebuilt the piping around what the house already had.
High-Efficiency Boiler Operation
The installed Lochinvar Noble is rated at 95% AFUE, providing a high-efficiency replacement for the older boiler while also handling domestic hot-water production.
The Heating System Was Considered as a Whole
This project was not just about taking one boiler out and putting another in.
We checked the radiant slab, evaluated the two types of heat distribution, rebuilt the primary piping, updated the venting and incorporated domestic hot water into the new system.
The Result of the Chelmsford Boiler Replacement
The homeowner now has one wall-mounted system providing both space heating and domestic hot water.
Before installing the new boiler, Pespisa confirmed that the older radiant tubing buried in the concrete slab could still hold pressure. The Lochinvar combi boiler was then connected to the home’s radiant and baseboard heating through rebuilt primary-loop piping.
Project Highlights
- Lochinvar Noble NKC150N natural gas combi boiler
- 150,000 BTU/hr input
- 95% AFUE
- Space heating and domestic hot water from one wall-mounted unit
- Radiant slab pressure tested at 25 PSI for 24 hours before installation
- Existing radiant floor heating retained
- Existing baseboard heating retained
- New primary-loop piping
- High-efficiency ECM circulators
- New expansion tank
- New Caleffi fill valve with backflow protection
- Outdoor-reset control
- Updated combustion-air and flue venting
- Separate storage water heater removed
- More usable floor space in the mechanical room
- Permits and inspection handled by Pespisa
- Completed July 2026
Chelmsford Boiler Replacement Project Details
Project Detail | Specification |
|---|---|
| Location | Chelmsford, MA |
| Project Type | Gas boiler replacement |
| Equipment | Lochinvar Noble natural gas combi boiler |
| Model | NKC150N |
| Input | 150,000 BTU/hr |
| Efficiency | 95% AFUE |
| Function | Space heating + domestic hot water |
| Mounting | Wall mounted |
| Heat Distribution | In-slab radiant floor + hydronic baseboard |
| Control | Lochinvar outdoor reset |
| Circulators | High-efficiency ECM circulators |
| Venting | Dedicated combustion-air intake + Centrotherm InnoFlue system |
| Pre-Installation Testing | Radiant loops pressure tested at 25 PSI for 24 hours |
| Additional Work | New gas line, primary-loop piping, expansion tank, fill/backflow valve and boiler-room baseboard |
| Permits | Pulled and inspected |
| Completed | July 2026 |
Veterans Appreciation Discount
This Chelmsford project included Pespisa’s Veterans Appreciation discount.
If you have served, ask our team about current discounts or other options that may apply to your project.
Need a Boiler Replacement in Chelmsford, MA?
If your boiler is leaking, short cycling or approaching the end of its service life, it is worth looking at more than the equipment itself.
Pespisa evaluates the heating system the boiler serves, including the piping, controls and heat distribution, before recommending replacement equipment.
If part of your home uses radiant tubing buried in a concrete slab, we can also evaluate the existing system before connecting a new boiler to it.
Pespisa provides boiler replacement and other heating and plumbing services in Chelmsford and surrounding Middlesex County communities.
Frequently Asked Questions
Can a combi boiler provide both home heating and hot water?
Yes. A combi boiler combines hydronic space heating and domestic hot-water production in one appliance. That allowed this Chelmsford home to replace both the boiler and separate water heater with one wall-mounted system.
Can one boiler serve radiant floor heat and baseboard?
Yes, depending on the design of the heating system. This home retained both its radiant-floor and baseboard heating, with the new boiler connected through rebuilt hydronic piping.
Why was the radiant floor tested before the new boiler was installed?
The radiant tubing was buried inside an older concrete slab. Pespisa isolated and pressure tested the loops first so their condition could be evaluated before the replacement boiler was installed.