Premature rooftop heat exchanger failures

RayWohlfarth

In addition to boilers, we also service and install packaged rooftop units. We are starting to see a troubling trend as the heat exchangers seem to be failing much quicker than the older units. It seems like once the units are ten years old, we start seeing cracks in the heat exchangers. We had an eight year old rooftop yesterday with cracks. Are you seeing this as well? Just curious in Pittsburgh
Thanks

EBEBRATT-Ed

It's all junk nowadays. I have often thought about running the indoor fan on continuous to help the hx expand and contract less violently, but people don't like cold air blowing on them.

Tim McElwain

When we try to gain efficiency by tightening up the sections of furnaces and rooftop equipment or using secondary heat exchangers to boost efficiency then we pay a price which is longevity of the heat exchangers.

RayWohlfarth

@EBEBRATT-Ed Its crazy to me that they think it's ok. I remember speaking with a manufacturer who said the industry was shooting for a 15 year life

RayWohlfarth

@Tim McElwain Guess they consider it a fair tradeoff

mattmia2

I don't think shorter life has to follow from higher efficiency. I think it is an easy scapegoat for corners that are cut in pushes to make the product cheaper and to meet a price point at the higher efficiency when there is more material and time necessary to make the higher efficiency product at the same quality.

pecmsg

The heat exchanger being down stream of the A/C coil causes excessive condensation. 

10 years is a good run out here. 

SuperTech

pecmsg said:

The heat exchanger being down stream of the A/C coil causes excessive condensation. 

10 years is a good run out here. 

This is definitely the problem that I see most often with package units. The heat exchangers don't necessarily crack but rust/rot out due to a very poor design. It seems like Carrier is aware of this and design their heat exchangers to be somewhat easy to replace. 

RayWohlfarth

@mattmia2 I believe costs cutting is the reason for the shorter life. I remember seeing a 30 year old boilers still working well
@pecmsg I just feel bad for my customers when i tell them their ten year old rooftop unit needs replaced.
@SuperTech I agree I just wish they made it easier to check the integrity. You have remove the top to gain access to the heat exchanger. We have started checking the heat exchangers on all units over 5 years old. We used a combustion analyzer and see if the O2 level rise when the fan starts

retiredguy

When I got into the HVAC business in 1968 straight out of tech school, as a service tech for a firm in Pittsburgh, Pa, we serviced everything heat and A/C residential. Their brands to sell were Lennox and Bryant and occasionally some Yorks. The stuff back then was made very well except for the American Standard Reddish color furnaces. Their heat exchangers cracked in just a couple years. It was great to find one of those since that meant a new furnace sale of which the service tech received a bonus. Around 1971 or 72 Lennox brought out their new line of "improved" furnaces. My boss installed a lot of these. Most of the time the heat exchangers did not make it through the first year warranty. Everyone installed had to have a replacement heat exchanger for which I was told that Lennox paid the whole tab. Most roof top units lasted for many years. Keeping the standing pilots lit was their problem. Back then a lot of the heat exchangers were stainless steel, porcelain coated, or aluminum coated (for an extra cost), to resist the rusting that usually happened at least in our area. I think a lot of it was caused by the atmosphere from the numerous steel mills.

Since I have been retired for about 15 years I can only guess that the heat exchangers that are cracking are of the "new technology" that are made to save money and be super efficient. I saw many cost saving changes to the construction of HVAC equipment over the years. A few cents of savings to a piece of equipment always "trumped" the quality of that item. I would also question the country of origin that is supplying the steel and the manufacturing.

RayWohlfarth

@retiredguy We worked on some of the old Lennox rooftops. They were a very rugged unit and the heat exchanger would last forever. the only gripe I had was they used the same black wire for everything. If you didnt have a wiring diagram, you had to trace each wire. Not fun on a cold or rainy day

EBEBRATT-Ed

And for a time, I remember Carrier units where every wire was yellow. The old stuff was built heavy duty compared to the new stuff, which is a tin box,

But as my boss always said a poor way to heat. A tin box out on a zero-degree roof with 1" (if that) of insulation in it.

@retiredguy

I remember some Climatrol units that had standing pilots. Every time the wind blew.........

SuperTech

Wow, I've heard of rooftop units that every wire was black. I was told they were marked or numbered and if you weren't careful you could rub the identification marking off the wires.

Fortunately I have never encountered any of these units, I've only been doing this for around 15 years. My instructor as an apprentice told me about them. I've only seen one or two rooftops with standing pilots, they really seemed like a poor design. 

It seems to me that the only units that are still made with quality are Thermopride oil furnaces. Unfortunately now oil heat is trying to be phased out. 

I do service one Thermopride package unit, not sure why they aren't more common. It seems like a good quality unit.

pedmec

Up here in the northeast we replace lots of rooftop heat exchangers as we work on a lot of restaurants and commercial buildings. Most of the the heat exchangers are carrier tubular heat exchangers that ain't cracked but pitted due to corrosion from inside the heat exchanger. A definite indication of condensation forming inside the heat exchanger. I chalk this up to cold ambient combustion air and the draft inducer design. In all my years of doing combustion induced draft equipment, when properly installed, runs with a lower flue gas temperature. you'll get condensation at start-up and if not running long enough wont dry out before acting on the heat exchanger. we have make up air units of all sizes that are fan assisted that form condensation when they are designed not to.

mattmia2

Could you buy a thermopride without a burner and put a gas power burner on it?

offdutytech

I would agree with the quality of some roof top units these days vs years ago have changed. Sure some of its manufactures cutting costs and new DOE standards. It's also people's understanding of HVAC systems over all when replacing equipment. Many just look at model numbers for replacing one RTU with another. They often don't take the time or have the knowledge to poke around and look at things like associated ductwork, economizer functions and control systems. Most manufactures have a life cycle for equipment, now it's a different story if it makes it that time frame depending on maintenance and how it was installed 

Solid_Fuel_Man

For the life of me, I cannot understand why anything which is in contact with the combustion process isn't stainless. So many RTUs I've worked on look like they are made of aluminized car exhaust pipe. The welded seams have surface rust in them when they are craned up on the roof, before we even get to connect the gas lines to them and fire them for the first time. 

I agree with @EBEBRATT-Ed old boss....a sheetmetal box with an inch of the nastiest fiberglass insulation on a snowy roof....great work! 

Back in the 80s we had an account with oil fired RTUs... oh that was fun! #2 oil was pushed up by lift pumps, those sooty things would gell the oil, lockout...or lockout and then gell up...we never knew which came first! I don't know who made them, but they never rotted out. 

Thankfully they were replaced with propane fired RTUs in the mid 90s. 

RayWohlfarth

@EBEBRATT-Ed Never saw any with standing pilots. I always wanted to take the person who designed these things on a rooftop service call in winter.
@SuperTech When I was able to get a wiring diagram from the factory, I made copies of it for the shop and the laminated a copy to keep in the unit
Here is the 8 year old unit

RayWohlfarth

@Solid_Fuel_Man wow that's sounded fun