CAT IV system

[Scott Patterson]

I attended a meeting on Friday, several home inspectors from around the country were in attendance and all had over 10 years+ experience as a home inspector. A couple of the inspectors who came from different ends of the country both said that a CAT IV furnace has an expected life of about 8-10 years. I had never heard this before.

One of the clues they gave about a CAT IV system is to look into the little viewing port and if you see any discoloring in the burn chambers that the unit has a problem and that it is most likely toast. I'm really thinking that this is true as both of the inspectors do a tremendous amount of EW work, one is from Right Coast and the other from the Left Coast!

I'm just curious as to what other folks have to say about CAT IV systems..

[Markus Keller]

I think they are full of crap.
- Manufacturer info I've looked at usually says +/- 15 years, some 20
- Seeing discoloration through the view port? It's usually a 3/4" to 1" glass opening. How are they going to see discoloration with the unit on or off? If unit is on, all the blue flames with mask anything. If off, it's dark, the flashlight reflects back and can't see squat. I've tried
- Flame discoloration (not blue) is another matter.
- I know of many cat iv older than 10 years
Can you imagine if that was true? I think the Manuf. would be looking at some serious public inquiry, even though the public is usually asleep.

[Nick Ostrowski]

If they are correct, that is a serious problem for the manufacturers and homeowners if you can only expect to get 8-10 years out of a furnace.

Scott, did these inspectors give you any indication as to what causes the life cycle of these furnaces to be cut so short and what the cause is of the corrosion?

[Scott Patterson]

If they are correct, that is a serious problem for the manufacturers and homeowners if you can only expect to get 8-10 years out of a furnace.

Scott, did these inspectors give you any indication as to what causes the life cycle of these furnaces to be cut so short and what the cause is of the corrosion?

Corrosion of the innards are the main problem and the thin metals that are used in the heat chamber.

I have seen many 10+ year old CAT IV units that appear to be working just fine. I really never give them much thought simply because their burn chambers are sealed and you just can't see all that much.

With the unit off you can shine your flashlight into the viewing port and you can see a little of the burn chamber.

FIW, a typical non CAT IV system in the Southern parts of the country can be expected to have around 10-12 years of useful life. In the South we just don't use them as much and they tend to rust-out more due to the lack of use.

[Bob Harper]

The alloys used in heat exhangers are a lot better than when these units first came out. AL29-4C stainless steel has a really good track record for HX. BTW, you cannot tell about the patency of a HX by viewing through the sightglass. It takes a qualified, trained technician to inspect and test HX.

There are a lot of factors that go into the life of a high efficiency furnace:
proper sizing
proper installation
proper maintenance
climatic zone
use in the home
type of thermostat
etc., etc.

You can have a perfectly installed system killed very quickly by a bird nest or ice dam in the vent termination.

Be careful inspecting heating appliances. Unless you perform a proper thorough comprehensive inspection and conduct performance testing, you leave yourself open. I can say that about a chimneys, too.
Bob

[Scott Patterson]

Be careful inspecting heating appliances. Unless you perform a proper thorough comprehensive inspection and conduct performance testing, you leave yourself open. I can say that about a chimneys, too.
Bob

Isn't that true with just about everything a home inspector does!