What size liner?

Cyclist77

As I look to have a SS liner installed my question is what size? The Weil-McClain CGa4 has a 5" flue. So is that the correct size I should use?

It is an interior chimney approximately 35 ft high.

Thanks!

HydronicMike

The installer will know.
Each manufacturer has directions on sizing requirements based on connector length, chimney height and total Btu’s

EdTheHeaterMan

NFPA 54 has the specifications. Don't take it upon yourself to do the job of the professional. The size of a chimney liner required by NFPA 54 depends on several factors, including the type of appliance being vented, the fuel type, and the specific venting system used. You know the size because you have selected the WM CGa4. but before you actually select that boiler, are you sure that it is not oversized for your needs?

Assuming that the proper heat loss calculation has been done and you know that your home has a heat loss of more than 52,000BTUh and less then 77,000 BTUh then the CGa4 is the proper size boiler for your home. Chances are, if you are replacing an existing boiler with the same size boiler, then the CGa-4 may be oversized.

The gas input of the CGa-4 is 105,000 BTUh so the gas piping and the venting must use that specification to select the proper size. Here is an excerpt from NFPA 54 published my MetalFab. These Venting tables indicate that if you are venting a single category I appliance that is rated at 105,000 BTU input when using a single wall vent connector (the connector is commonly called the "smoke pipe" that connects the draft hood to the chimney base) you must have a minimum diameter of 5" diameter based on table 6, and should not be larger than 12" diameter. There is some disagreement as the the maximum size number and I refer that issue to @Bob Harper, the Venting Expert on HeatingHelp.com.

However, I believe that Maximum size is not the issue for you. You just want to know the minimum size in order to select the proper liner size and 5" will do it. Now sliding a 5" corrugated liner into that chimney will actually reduce the free area to something like that of a 4.5" diameter smooth pipe. So I might opt for a 5.5" corrugated liner. Or you can line the chimney with 5" smooth pipe sections and hope you don't get stuck half way thru the project. 6" will also do it if you can fit it down your chimney. The larger one will allow you to add another gas appliance in the event that you want to add a water heater to that chimney in the future.

I hope this helps.

Still believe that you should leave it to the experts

EBEBRATT-Ed

If you install the same size liner as the boiler flue you will always be ok. If someone checks the sizing based on the chimney height you can sometimes go smaller

Bob Harper

I would recommend a 5" smooth wall flexible 316L or 316Ti ss liner. You have to de-rate corrugated liners 20% meaning a 5.5" ID to equate to a 5" round. You could use rigid round ss but it would have to be a straight drop without offsets or snags. However, with the advent of smoothwall flexible liners, I do not see a good reason, other than a few bucks difference in cost, why someone would want to use a corrugated liner. Corrugated liners tend to snag and hang up going down. They are more flexible than smoothwall.

As for the vent connector (stove pipe or smoke pipe), I recommend rigid round ss 26 ga. chimney liner or type L vent. This makes for a permanent connector to a permanent liner with a lifetime warranty (often transferrable). The ss does not conduct heat well so it results in slightly higher stack temps. This stabilizes and may slightly increase draft but it reduces flue gas condensation. If you get condensation, the 316L ss can handle it. BTW, use the 400 series ss drill point TEK screws, 3 min. spaced equidistantly with no screws or seams btw 5-7 O'clock on horizontal runs. Support all offsets and horizontal runs over 6 feet.

Advanced installation would block off the integral draft hood and install a tee with a double acting barometric damper that has the boiler's own spill switch attached at the mouth of the gate. This will void the warranty on the boiler should anything go wrong WHERE THE MODIFICATION IS FOUND TO BE THE PROXIMATE CAUSE of the loss. If it cannot be proved to be the cause then its fine. I've never heard of this causing a problem nor has Jim Davis, the leading expert in CO but it has solved a multitude of problems and made installations much safer.

Back to the liner: it will require a stainless-steel top support plate trimmed to sit on the top of the flue tile adhered with silicone caulk. A mating ss removable cap with mesh animal guard and rain lid tops it off. Have the installer pack high temp insulation, such as rockwool or ceramic fiber around the liner at the top. This blocks cold air and bug infiltration but also holds the liner straight up. If you don't do this the liner may tilt. At the base, just sweep it into the room like a hockey stick- no tee or cleanout needed. Pack the base with insulation. The broad radius sweep at the base is actually accounted for in the sizing charts in the gas code. Note those charts are for INTERIOR chimneys only. A liner installed without a full length insulation blanket but sealed at both ends creates a 'Dewar's Flask' or Thermos bottle effect, keeping the liner warm. A hot flue is a happy flue.

Make sure you have sufficient MakeUp Air so the Combustion Appliance Zone (CAZ) is neutral to slightly positive. Install low level CO monitors on each floor and outside all sleeping rooms. Have a qualified pro perform combustion analysis adjusting the chimney draft prn.

These guys here can make a lot of other good recommendations on near boiler piping such as 'pumping away', bypasses, purge valves, isolation valves, strainers, water feed backfllow prevention, outdoor reset (ODR). how to set up the thermostat and aquastat, etc. to get the best installation.

For most chimneys, a 5" sw ss liner will slide right down. However, the national std., NFPA 211 calls for a level II inspection first, which a qualified chimney pro can handle first to advise on the liner based upon those findings.

HTH, Bob

Cyclist77

Thaks for the replies!

I was thinking 5" would do it and had planned on doing it myself with a few helpers. But after pricing out the components I got a price from a local chimney fellow and he is only about $450 more and he is quoting a 6".