Tag Archives: heat exchange

Cleaning heat exchanger coils

The troubleshooting of our busted boiler (a Trinity LX150 by NTI), led me to the fact that mineral deposits inside the heat exchanger led to partial or complete blockage.

I knew that I had to clean out those mineral deposits, but I wasn’t able to get my hands on the recommended Fernox DS-40 descaler and cleanser – at least not quickly.

My next best option was to use widely available cleaning vinegar. But for this to work I had to isolate the boiler. In other words, I needed to just flush the boiler with the cleaning vinegar, but not the whole hydronic heating system, because that would take gallons upon gallons of cleaning vinegar.

Isolating and flushing the boiler should have been a cake walk, if our boiler had been installed with the drain and isolation valves as shown in the nifty manufacturer-issued plumbing diagram.

The reality of our boiler plumbing required a little creativity, because I only had one isolation valve and did not have drain valves as shown in the diagram.

I isolated the boiler by turning off the isolation valve on the outlet side, and turning off the isolation valves for the boiler pump on the inlet side. Removing the boiler pump was the best substitute available for the missing drain valve.

I then proceeded to remove the pressure relief valve on the outlet side and replace it with a simple ½ inch riser.

By pouring about one gallon of cleaning vinegar into the boiler through the riser, I was able to displace the water in the boiler and heat exchanger.

I added about another gallon or two into the bucket below the boiler pump, set my small sump pump into the bucket, and connected it with a vinyl tube to the riser on the outlet side. With this setup I was able to start flushing the boiler in reverse (outlet to inlet) with almost pure cleaning vinegar.

I also added a small wire tray to monitor the debris discharge. It took me three days of boiler flushing to get the mineral deposits out of the heat exchanger. I actually flushed for four days, but had no more debris discharge on day four.

And don’t be fooled by the rapid flow rate in the video, which I took on day four. On day one, I had a fraction of that flow and the sump pump was cranking pretty hard.

How did we get by without a boiler for three days?

That was thanks to the resilience of our system. We didn’t use any hydronic heating during the three days of boiler maintenance, but instead relied on our minisplits for heating.

And what about domestic hot water?

After each day of flushing, I reconnected the boiler and turned it back on to recharge our buffer tank and domestic hot water storage tank. With both tanks recharged, we had enough domestic hot water for a day.

I sat with the boiler during the flushing process and manually turned it off to let it cool down once there was a hint of hammering. It was time consuming but it worked.

I also noticed during the three days that the boiler operation got increasingly more quiet. Not only did the hammering and banging cease, but so did the hissing of flowing water. With the obstructions in the heat exchanger removed, our boiler ran almost silently and very efficiently once again.

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Busted Boiler

How about a seasonal topic, like a busted boiler?

Our Trinity LX150 by NTI (NY Thermal Inc.) started hammering and banging and eventually shut down. When I checked the boiler display, I found an error message saying: “Lockout 81 – Delta T limit”.

At the time I had no idea what the cause of the problem could be. So I started with the troubleshooting chart in the operation instructions, which was pretty straight forward:

I tested “Fuse A” and it was fine. I checked the pump, and it was running. The plumbing was correct too and I had water pressure of 20 psi. That left me with the dreaded last option: a fouled heat exchanger. Dreaded, because I wasn’t quite clear on what it meant and what the implications were. After some research and scouring through YouTube, I finally was able to put the pieces together.

A boiler doesn’t just break. It usually has a good reason, such as deferred maintenance. And I am embarrassed to admit that I am guilty of such deferral.

Our high efficiency boiler (Trinity LX150) takes care of our domestic hot water and hydronic heating system. I wrote about our mechanical system and how it functions in a previous blog post, which makes for good reading.

The boiler has a modulating capacity from 25,000 to 150,000 BTU and a stainless steel heat exchanger.

It is that heat exchanger that makes these boilers so efficient. In our case, we have small tubing (probably 3/8″) that surrounds the burn chamber. The ratio of the small water volume in the heat exchanger versus the relatively large surface area of the heat exchanger allows for efficient heat transfer.

But this efficiency comes at a price. Because of the small diameter, the tubing can be prone to clogging by lime and other mineral deposits. And once deposits build up inside the heat exchanger tubing, the efficiency of the boiler goes down and the banging and hammering starts.

If the water in the closed loop hydronic system would be treated properly, the risk of mineral deposit formation would be greatly reduced.

When our installer first filled the hydronic system, he added an additive that depletes the oxygen in the water and reduces the risk of corrosion and mineral deposit formation. From that point on, the closed loop system was supposed to run almost maintenance free, as long as no new water (i.e new oxygen and minerals) was added to the system.

Read also: RPA – Chemical Water Treatment

But I did add new water. First when we filled and started up the radiators on the 1st floor, and again later when I partially drained the buffer tank to service a sensor. I did not think about the newly introduced water at the time, and it came around to nip me in the butt!

The first symptoms were the hammering and banging in the boiler. I assume what happened was that the tube diameter was decreased by mineral deposits to the point where the flow volume was so small and slow that the water turned into steam. That’s a very unnerving thought!

The boiler has an amazing array of safety sensors and mechanisms. It recognized the dangerously high temperature in the heat exchanger and automatically shut off.

That is good for safety, but it is not good for maintaining domestic hot water and keeping the radiators running.

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Welcome waste (energy)

Today, we are not pinching nickels, but degrees.

I mentioned in the last post that it took us until November 17 before we turned the heat on, whereas other Chicagoans fired up their furnaces in early October. Why were we still comfortable several weeks into the cold weather?

Waste heat!

Boiling the kettle, cooking dinner, baking banana bread … Then add in all the electrical appliances that produce waste heat: running the fridge, TV, laptop and desktop computers, having the lights on … all this and more produce some level of waste heat which is welcome during this season. Not so much during the dog days of summer, though.

But wait! There’s more. Let’s not ignore the four critters occupying the space. Two of them two legged, and the other two four legged. Believe me, they all have a healthy metabolism going, based on the heat they throw off! Seriously, body heat from building occupants is not to be ignored – not in the context of a deep energy retrofit.

Let’s think of these heat sources as miniature radiators. Individually, they don’t do much. But cumulatively they begin to matter, if – and this is a big IF – the building is well insulated  and as good as airtight. Because now this waste heat doesn’t escape. It lingers around and keeps the building interior at a comfortable temperature when others have long reached for their thermostats.

In this context, your furnishing and the actual interior of your building begins to act as a heat sink – it becomes thermal mass. Your oak dresser, your hardwood floors, your drywall, your bathroom tiles, you name it – they all store heat to some degree, which adds to the comfort.

Another gadget that helps us to delay the start of the heating season in the Energy Recovery Ventilator (ERV). It delivers fresh air into our airtight building envelope, but does so with the help of a heat exchanger. This allow us to recover most of the precious waste heat and yet still get fresh air.

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Cool ideas?

Sometimes I get these seemingly insane ideas, only to find out later that they were somewhat rational. The subject matter of those ideas is typically not my strong suit. That’s why I tend to be infuriatingly quick to dismiss them.

Air conditioning is on my list of subjects that are not my strong suit. I grew up in Germany, where air conditioning is virtually non-existent. I ran into active cooling for the first time while visiting the Caribbean, and again years later when I moved to Chicago.

I regard summer air conditioning in the Midwest as a necessary evil and have a pronounced dislike for the temperature extremes we have to tolerate between the outdoors and conditioned indoors. I dread stepping into a grocery store or office building that feels like an ice box.

Since we started our deep energy retrofit, I’ve had to wrestle with the question on how we will keep cool during the dog days of summer without creating an ice box. I quickly learned that “cool” is somewhat secondary. The primary problem to tackle is how to keep the relative humidity at a comfortable level, i.e. under 60% (preferably at 50%).

We already have an Energy Recovery Ventilator (ERV) that supplies fresh air into the house, yet keeps the outside heat and mugginess at bay. My seemingly insane idea was to install an air-to-water heat exchanger in the fresh air supply duct to remove humidity through condensation, and deliver pleasantly dry air into the house through the ERV duct system.

Simply put, I wanted to run the muggy outside air across a cold air conditioning coil to dry it out. But I was told that there was no such air conditioning device that could be combined with an ERV. Yet, I clearly wasn’t alone with this idea.

Just in the past couple of years I started reading about ‘Magic Boxes’ that basically combine the function of an ERV, or HRV (Heat Recovery Ventilator), with that of a small air-to-air heat pump, i.e. a small air conditioner.



Unlike our ERV, which uses and enthalpy wheel as a heat exchanger, a Magic Box uses an integrated air-source heat pump to transfer thermal energy between air streams. But they also can provide some additional limited conditioning – additional cooling (and drying) as well as heating.

One company (Build Equinox), located two and a half hours south of us, brought the CERV (Conditioning Energy Recovery Ventilator) to market just a few years ago. The CERV has an advertised heating capacity of 3,850 Btu/h, and cooling capacity of 2,400 Btu/h. These numbers vary depending on outdoor temperatures. One article listed a price of $4,500 for the CERV.

A competing product is the Boreal 12000 by Minotair out of Quebec, Canada. This Magic Box is more compact than the CERV and, in heat pump mode, has a listed heating and cooling capacity of 9,400 Btu/h and 8,700 Btu/h respectively. I read one article that pointed to a price of around $3,200 for the Boreal 12000.

Either the CERV or Boreal 12000 could be used instead of an ERV or HRV.

Going back to my original idea, combining an air-to-water heat exchanger with our existing ERV, I came across what looked like a promising option. An article on GreenBuilidngAdvisor.com described a variety of air-to-water heat pumps that could provide chilled water to the air-to-water heat exchanger.

In this function, the air-to-water heat pump would basically function as a chiller. But it could also reverse its cycle and produce hot water for domestic hot water consumption or a hydronic heating system.

The challenge would be to find a right sized unit that I could combine with our ERV, and that would be affordable. If you thought the CERV or Boreal 12000 were expensive, prepare yourself for a sticker shock while shopping for air-to-water heat pumps.

Nevertheless, I feel vindicated that my idea wasn’t that insane after all. But it has only brought me somewhat closer to a solution that would provide cooling and a comfortably low relative humidity during the dog days of summer in our deep energy retrofit.

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ERV croaked – Part 4a

I am having fun with my sequential blog post titles … maybe to compensate for the inconvenience of having a sequential problem with our Energy Recovery Ventilator (ERV).

Both of our ERVs (both RecoupAerator by UltimateAir) have been running flawlessly for the past two years. But earlier this month, our 1st floor ERV showed symptoms that were reminiscent of the problems we had during the winter of 2013/14 with our basement unit.

When we ran the ERV, the building cooled down rather quickly. That indicated that something was amiss with the heat exchanging process. Based on our past experience, I knew that there were two probable causes:

  1. The enthalpy wheel stopped running.
  2. One of the blower motors and/or control boards croaked.

Well, it took no time at all to determine that it was the motor and/or control board. I made a quick call to UltimateAir and a few days later we received the replacement parts. It was time to start tinkering again:

I have a suspicion that the problem may lay with the heat sink on the control board. Two years ago, when I went through the same process in the basement, I noticed that the replacement board had a significantly bigger heat sink than the original board. I also recall vaguely that Matt at UltimateAir pointed out that the board on our 1st ERV may give us the same problem.


Or was it the fibers from the enthalpy wheel that started clogging the impeller that did the motor in? I am curious to know that the experts at UltimateAir think.

On a side note – this blog begins to pay off! Because everything is documented, it’s easy to look up a problem of the past to remind myself on how to fix things – like the ERV.

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