An orphaned water heater is when the furnace is replaced with a side wall vent model leaving the old "atmospherically-vented” gas water heater alone with a too big of a chimney or flue for the small amount of heat output it releases alone. An orphaned water heater in an over sized chimney creates a huge moisture problem. The problem also lays in the lack of draft when the furnace isn’t running or in summer months and the negative pressure in the house doesn’t allow the flue gases to vent out properly. The draft being reduced will result in water vapor found in the flue gas combining with the sulfur in the flue gas to created sulfur acid that will ruin your flue and chimney.
NFPA 54 and 211 deal with chimney standards and sizing for the flue. Size, height, exposure (inside the structure, partially exposed or outside) and localized weather conditions all come into play, so there are no one-size-fits-all categories. A three-story chimney will behave differently from a two-story or one story chimney. Unlined chimneys vs lined chimneys, and so on.
INTERNATION FUEL GAS CODE 2006 SECTION 501.15 EXISTING CHIMNEY AND VENTS. WHERE AN APPLIANCE IS PERMANENTLY DISCONNECT FROM AN EXISTING CHIMNEY OR VENT, THE CHIMNEY OR VENT SHALL COMPLY WITH SECTION 501.15.1. SIZE. The chimney or vent shall be resized as necessary to control flue gas condensation in the interior chimney or vent and to provide the appliance served with proper draft.
There is, however, a somewhat reliable rule of thumb to give us a line that we should not cross where safety is paramount: the chimney’s dimension should not exceed the connecting flue’s dimension by more than seven to- one. In other words, the square inch area of the chimney must not be more than seven times greater than the flue piping. A 3-in. water heater flue is just a bit more than 7-sq.in., so the chimney must not be greater than 49-sq.in.; a 4-in. diameter flue is 12.588-sq.in. and its corresponding chimney flue limit is just over 88-sq.in. Those old 8 x 8 or 8 x 12 or 10 x 10 chimneys will lead to sustained flue gas condensation, damage the chimney and — eventually — result in property damage.
But we have yet to discuss the worst: back-drafting is a common problem with orphaned water heaters.
ANSI Z21.10.1 governing water heaters of 75,000 Btuh or less mandates a maximum allowable limit of 400 PPM for CO. The U.S. Department of Energy allows for one-minute of back-drafting for orphaned water heaters — maximum.
Lawyers don’t ignore this If you’re ignoring orphaned water heaters, lawyers and liability experts are not and you’d be wise to install a chimney liners. The rules also state that orphaned water heaters vented into an unlined or tile lined masonry chimney require the installation of a properly sized liner. Homeowner's need to know, You need a chimney liner because your chimney is unlined brick or over sized; its flue is too large to support proper drafting of combustion flue gases, which include carbon monoxide a deadly gas that can enter your home. It’s required by a number of codes. The other alternative would be to add a new direct-vent gas water heater or an electric water heater and abandon the chimney completely.”
I'm replacing our old heater with a new 95% efficient system that will vent out the side of the house using a PVC pipe, leaving the water heater orphaned on the chimney. I'm told I need to get a chimney liner to protect myself from carbon monoxide, protect my chimney from corrosion, and be in compliance with building and safety code. All well and good, and I'm going to do it. However I am totally confused about one thing. Every summer the current heater has been off for months on end, effectively leaving the water heater orphaned at that time. Why isn't this also considered hazardous to life and the chimney? What's so special about having the furnace gone year round that suddenly a liner is required?
You are right to question this. Water heaters are the single most dangerous appliance in your home for this very reason. Chimneys can often become unsafe. They most often cause water heater flue gas spillage in the summer because they cannot produce enough of their own draft while operating alone. It's just one of those things that we blindly accept in this industry and misunderstood by many builders and heating contractors. Nobody wants to change it, even if it is unsafe.
Although, there are field modifications available that will make a water heater much safer (Properly Sized Stainless Steel Liners). Unfortunately, most people do not understand the how and why to do it.
In an inspection yesterday I found an orphaned gas water heater. The typical scenario where the original old gas furnace was replaced the year before with a high efficiency side wall vented gas furnace . The new furnace has a new plastic vent pipe, and the metal T connector in the original metal vent pipe has been capped where the old furnace vent pipe connected to the masonry chimney. White effervescent trails ran from the chimney’s base down the wall and the same white powdery substance was evident at each joint in the combined flue piping. The metal flue pipe was paper thin with holes in it. It was a classic example of flue gas condensation, which contains sulfuric acids. For every 100,000 Btu of combustion, a gallon of condensate can be generated!
In Bucks County, Pa., I have found many orphaned water heater's back drafting in basements. But in this case the Water Heater is in a heater room and the vent pipe has a short, straight vertical run. So if this is a real concern, why hasn't it always been a concern for the 6 months every year that the furnace is not operating? I suppose the hot weather/attic in the summer could affect venting (compared to a very cold attic), but there are plenty of days here that are cool, but not enough to operate the furnace. Proper draft is all ways the issue, with out the right draft flue gases and carbon monoxide can enter the house causing carbon monoxide poisoning and death.
In explaining why it's a concern (the Gas Water Heater with a 3" or 4" draft hood does not generate enough heat to properly (draft in such a large vent pipe) and a masonry chimney is even worse, I think it's a logical question to ask why this would not be a concern anytime the furnace sharing the vent pipe was not operating.
The best option and it is often cheaper than installing a new vent system and definitely less than a installing a new water heater.
At JC Heating we reline many chimneys - older homes mostly with masonry chimneys with terracotta liners. Standard protocol is to reline the chimney with a stainless liner sized to the BTU input of the gas water heater, the liner running from the top of the chimney down to the water heater.
If you are looking for help in the Bucks County or Montgomery County, Pa. area to get your Chimney relined, we can help! JC Heating is a Certified Chimney Sweep and does this replacement many times a year. We can also inspect your chimney and explain your options for you too.
The CSIA Certified Chimney Sweep® credential is the measure of a chimney sweep’s knowledge about the evaluation and maintenance of chimney and venting systems, and is acknowledged by industry organizations, insurance underwriters, local, state and federal agencies as the measure of a chimney sweep’s knowledge about the evaluation and maintenance of chimney and venting systems