The Glitch & The Fix

Can you find the problems with this space heating set-up?

hydronicpros@gmail.com (John Siegenthaler, P.E.) — Tue, 31 Mar 2026 17:00:23 -0400

Can you identify some problems that are likely with this set up, and propose an alternative design to eliminate any such problems?

The Glitch & The Fix: Troubleshooting hydronic piping mistakes in panel radiator systems

hydronicpros@gmail.com (John Siegenthaler, P.E.) — Wed, 04 Mar 2026 00:00:00 -0500

Figure 1 shows a hydronic system that’s intended to supply four panel radiators, each with their own thermostatic radiator valve and an indirect water heater from a gas-fired sectional cast-iron boiler. The system is designed using primary/secondary piping. The primary circulator operates whenever the space heating load or the indirect water heater call for heat.

Bewitched Btus: Understanding the hydraulic consequences of improper primary loop design

hydronicpros@gmail.com (John Siegenthaler, P.E.) — Wed, 04 Feb 2026 00:00:00 -0500

Figure 1 shows the piping layout for an actual installation. It uses two boilers, fired in stages, to supply three areas of a building. One of those areas is sub-divided into three zones. The other two areas are handled by individual zone circulators. The "primary circulator" operates whenever any load circuit is on. All circulators are fixed speed. There's a partially closed ball valve at the end of the "primary loop."

The Glitch & The Fix: Geo-normous problems

hydronicpros@gmail.com (John Siegenthaler, P.E.) — Wed, 07 Jan 2026 11:44:23 -0500

Single-stage non-modulating heat sources in zoned distribution systems often face short cycling, particularly with low thermal mass. When few zones are active, they struggle to dissipate generated heat quickly, causing temperature build-up and potential shutdown of the heat pump based on internal limits, with varied restart behavior depending on controls.

The Glitch & The Fix: Zone 3 failure

hydronicpros@gmail.com (John Siegenthaler, P.E.) — Tue, 16 Dec 2025 00:00:00 -0500

Can you speculate why heat delivery in zone 3 was insufficient before the helper pump? How could the piping system be improved, considering the wasted length of PEX-AL-PEX tubing from the manifolds to the floor panels in figure 2?

Overlooped: Boiler swap gone wrong

hydronicpros@gmail.com (John Siegenthaler, P.E.) — Tue, 04 Nov 2025 00:00:00 -0500

An owner, who has never been satisfied with the performance of his heating system, decides that the boiler must be the root cause of all the performance issues. Not wanting to spend any more than necessary, he makes several calls looking for the lowest boiler replacement price.

Hindsight - From complex loops to clean headers: simplifying for reliability

hydronicpros@gmail.com (John Siegenthaler, P.E.) — Mon, 13 Oct 2025 01:00:00 -0400

Around 25 years ago, I developed a design that sends high-temperature water to a remote manifold for low-temperature floor heating, mixing it with returning water to achieve the optimal supply temperature, regulated by a variable speed pump. Can you identify a problem with this approach or propose a better one?

Right & wrong: Examining common design pitfalls, and how to optimize piping strategies

hydronicpros@gmail.com (John Siegenthaler, P.E.) — Wed, 01 Oct 2025 00:00:00 -0400

These are common design pitfalls that may seem effective as they are. Review them and identify changes that could enhance the layout.

Hydronic heating glitch solved: Why adding a circulator won't fix primary loop flow issue

hydronicpros@gmail.com (John Siegenthaler, P.E.) — Thu, 08 May 2025 00:00:00 -0400

When the system was operated, the owner complained of flow problems. The heat emitters in any given zone were only marginally warmed when their associated zone circulator was operating. The owner questioned if another circulator should be installed.

Unexpected results: heat pump system at low outdoor temperatures

hydronicpros@gmail.com (John Siegenthaler, P.E.) — Fri, 04 Apr 2025 00:00:00 -0400

When only the air handler is operating the heat pump is able to supply the 120 ºF water. However, when the floor heating zone and the air handler are operating at the same time and the outdoor air temperature is below 24 ºF the fluid temperature leaving the heat pump can’t climb above 103 ºF. Why is this happening, and what can be done?

OK - At a glance: three zone radiant floor heating system

hydronicpros@gmail.com (John Siegenthaler, P.E.) — Mon, 31 Mar 2025 00:00:00 -0400

Can you spot several details that are either incorrect or missing? Can you propose an alternative design that would accomplish the same goals using less hardware?

A heat pump heat migration problem

hydronicpros@gmail.com (John Siegenthaler, P.E.) — Fri, 28 Feb 2025 00:00:00 -0500

A heating contractor is installing two air-to-water heat pumps as the primary heat source in a large home's hydronic system, keeping the existing boiler as backup. However, problems like heat migration into off zones and corrosion of the vent connector suggest design flaws that need to be addressed.

A hydro-split air-to-water heat pump system that ‘sorta’ works

Mon, 27 Jan 2025 00:00:00 -0500

Occupants of a building using a hydro-split air-to-water heat pump are facing slow recovery after night setbacks and inadequate hot water during peak demand. The system, composed of an outdoor and indoor unit, struggles with heating efficiency. What improvements could enhance its performance?

How would you fix this oil-fired boiler system?

Mon, 23 Dec 2024 00:00:00 -0500

The first photo shows an oil-fired boiler and surrounding details. Take a close look, and make a list of what you would change in this portion of the system.

Installation nightmare — how many problems can you spot?

Wed, 27 Nov 2024 00:00:00 -0500

The photo in Figure 1 shows a non-pressurized outdoor wood-fired furnace connected to a floor heating subsystem via two PEX tubes. It includes a cast iron circulator, a thermostatic 3-way valve for mixing, a bypass linking supply and return tubes, and an "expansion zone" for another floor heating circuit. This setup is in a multi-million dollar home. Are there any potential issues with the installation?

One size doesn't fit all when it comes to piping sizes

hydronicpros@gmail.com (John Siegenthaler, P.E.) — Tue, 29 Oct 2024 00:00:00 -0400

A project needs medium- and low-temperature radiant floor panels. The installer proposes using a mod/con boiler with a 1-inch tempering valve for lower temperatures and plans to pipe the entire system with 1-inch tubing. What potential issues could arise from this design?

The Glitch & The Fix: Identify the flow problems

Fri, 27 Sep 2024 00:00:00 -0400

The two photos below were from the same project. Flow is upward through the vertical pipe in Figure 1. Without any more details being described, can you spot at least two problems in each photo?

The Glitch & The Fix: Boiler choke point

Mon, 06 May 2024 00:00:00 -0400

Due to its low efficiency and high emissions, an installer is asked to replace the outdoor wood-fired furnace with a new cordwood gasification boiler.

Concrete slab over radiant tubing — who takes the blame?

Wed, 24 Apr 2024 00:00:00 -0400

Take a look at the two photos in Figure 1. Do you see any installation practices that might compromise the eventual structural or thermal performance of this slab?

Dual boiler layout shortcomings

Wed, 27 Mar 2024 00:00:00 -0400

An installer is asked to pipe up two larger commercial air handlers supplied by a dual boiler sub-system. The building owner wants to make it possible to supply either air handler from either boiler. Can you spot some shortcomings and suggest a better way to accomplish the same objectives?

3-zone radiant system peppered with problems

Wed, 21 Feb 2024 00:00:00 -0500

The installer is tasked with setting up a three-zone radiant floor heating system using a 5-ton geothermal heat pump and a mod/con boiler, connected through a primary-secondary system with closely spaced tees. The system includes 4 earth loops of 1” HDPE tubing, each 500 feet long, supplying the heat pump, and features underfloor tubing with aluminum plates.

Eliminating the temperature drop effect

Wed, 03 Jan 2024 00:00:00 -0500

A hydronics newbie decides that he can eliminate the temperature drop effect by putting all three supply-side tees upstream of all three return-side tees. If you don’t think it will work, what would you do to change it?

The Glitch & The Fix: Radiator Redo

Tue, 26 Dec 2023 00:00:00 -0500

An installer inspects a system where an aging steam boiler supplies several cast-iron radiators. He proposes to convert the system from steam to hot water and replace the old boiler with a mod/con boiler. Can you spot some potential problems and suggest some improvements?

Considerations for reusing existing distribution systems when upgrading equipment

Tue, 28 Nov 2023 00:00:00 -0500

An installer is asked to replace two aging cast-iron boilers with two mod/con boilers, but reuse as much of the existing distribution system as possible. Can you spot several details, omissions or other quirks that will lead to problems over the life of this system?

The Glitch & The Fix: Preventing fly ash accumulation

Wed, 25 Oct 2023 00:00:00 -0400

Can you diagnose why this glitch is happening, and suggest alternate methods for constructing this portion of the system?

The Glitch & The Fix: Circulator problems

Thu, 28 Sep 2023 00:00:00 -0400

Can you diagnose why this glitch is happening, and suggest alternate methods for constructing this portion of the system?

The Glitch & The Fix: Upside down

Mon, 29 May 2023 00:00:00 -0400

Take a look at Figures 1, 2a and 2b. What do they have in common? Can you think of some better ways to accommodate the flexible tubing?

The Glitch & The Fix: One size doesn't fit all

Mon, 03 Apr 2023 00:00:00 -0400

Can you spot at least six design or installation details that are going to create problems?

The Glitch & The Fix: Backed-up Btu

Tue, 28 Mar 2023 00:00:00 -0400

Are you an ace troubleshooter? We pose a question to you, our readers, to review a system’s schematic layout and discover its faults, flaws and defects.

The Glitch + The Fix: This almost got built

Wed, 22 Feb 2023 00:00:00 -0500

A recent inquiry involved a heating system for a school in which two electric boilers were being added to supplement the output of a gas-fired cast-iron boiler, and take advantage of low “off-peak” electrical rates.