Steven - I find this absolutely amazing.  It just seems like a real duhhhhh.  I would have thought that chimneys that are not properly cleaned with a large build up of creosote would have been a bigger problem.  Go figure!?

They are both big problems.  One additional thing we see a lot of here is deteriorated mortar.  Most brick chimneys in older houses here were built using lime mortar.  Over time, the lime leaches out and you end up with sand.  When I removed my own chimney, all the way to the basement, I was able to easily do it in a day because I just had to lift each brick off with my hand.  The mortar was toast.

David,

I'm back!;-) I would disagree with you in part about the need for caps on chimneys. Most specifically on a heating flue for oil fired appliances. They can cause problems with venting and condensation.

Sometimes, when a metal chimney connects into a masonry chimney, one will see rust and a big leak or drips around and below the metal pipe.

Often what are thought to be rust stains are in fact condensation stains from flue gases. Putting a cap on a chimney flue with this condition will exacerbate the problem. The solution may be to simply clean the flue or in more extreme cases inserting a stainless steel liner.

The reason this occurs is newer heating systems are more efficient. What this means is the heat from the burner is better utilized and the flue gases are much cooler. The gases in the flue (which contain water) cool down to quickly to exit the chimney effectively. The ideal temperature at the top of the flue should be 180 degrees.

Long chimneys, large area flues, exterior chimneys can all contribute to this problem. In my area now it is becoming a common practice when a new heating system is installed to also install a liner in the chimney. I find this on both gas or oil fired units. A properly sized, round liner will vent flue gas much better than the large, rectangular chimney liner.

As far as capping a fireplace flue, good idea.

James, This isn't my post but I will respond to your comments.  You speak as though you live in an area where heating oil is a common fuel.  In this area, the only oil heaters extant are all very old.  New furnaces are almost all either natural gas or propane.  The high efficiency furnaces with those fuels use PVC for the flue since most of the heat is removed from the exhaust.  What Steve was talking about above is not condensate, but rust, on specifically, wood burning fireplaces.  Again, I believe it is important to read the whole post and to know about the geographical area that is being spoken of.

David,

Oil is very common in my area. But I did say that in my post, so if this doesn't apply to your area that's fine, but it may in other areas and the blog wasn't being region specific. Some of what I said is relative weather your in WA or any where concerning venting into masonry chimneys.

Long chimneys, large area flues, exterior chimneys can all contribute to this problem. In my area now it is becoming a common practice when a new heating system is installed to also install a liner in the chimney. I find this on both gas or oil fired units. A properly sized, round liner will vent flue gas much better than the large, rectangular chimney liner.

This especially important now as the systems are becoming more efficient and the flue gas consequently cooler.

Also I'm sorry I meant to address my reply to Steven. I seem to get you two guys mixed up.

James, I have no argument with the concept of flue gases getting too cool in an improperly sized chimney for gas and oil.  This specific one was about  wood burning fire places.  Any competent HVAC installer knows that to vent a furnace (gas or oil) into an unlined chimney a properly sized metal liner must be installed.

David,

I wasn't referring to unlined chimneys, although if they are unlined they are old and almost always very far gone and dangerous. And don't be to sure about HVAC installers.

I have a good relationship with an instructor here for the oil heating trade. The guy is an invaluable resource and an unending source of good information and knowledge. Heating guys do not generally know about or bother to check chimneys before installing a system. What the instructor tells all his students is to have a level 2 interior chimney inspection done by a sweep or mason before beginning any work. Also to confer with the chimney guy on the sizing of the system to properly and safely vent it.

As I was saying a chimney flue can be too large which can be as equally dangerous as to small flue. That is the reason (too large) that new heating system installations are beginning to have flue liners installed. The industry is catching on to this problem.

James, I know nothing about your area, but I do know about this area.  All new furnace installs here must meet local codes, which include the size, material and location of flues.  High efficiency, as I stated before, use PVC.  All others use a properly sized B vent.  There are no, to my knowledge, new installs of oil furnaces here.  The only situation where the HVAC company would not change the chimney is if they were doing repairs on an existing furnace.

James,

In light of the discussion about qualifying information to a region, due to regional concerns with another blogger this weekend, I thought I put out a valiant effort to make it clear this was meant for my area.

The intro and topic was preceeded by "Bellingham WA home inspections", which I usually add on when I am focusing on the northwest and my territory. Add to that, the first line talked about inspections in Bellingham, Whatcom county and the great Pacific Northwet, which is a term we locals sometimes use for Pacific Northwest.

As David said, around here there are basically two calls related to this (1) put a rain cap on the chimney for the wood burning device (2) put a liner in for your gas furnace. As inspectors we see water heaters and furnaces vented into masonry chimneys and we call either as a defect period. They can choose to make it an issue or not, but that is the recommendation.

Thanks.

Steve