How Do You Calculate What Size Chimney Liner You Need?

Chimney/Vent Sizing Tables & Formulas
Home Page

POST a QUESTION or COMMENT most size requirements for chimney flues

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Chimney & flue sizing tables by type, BTUH, building codes, and other gene:

This article series describes the size requirements for chimney flues for different categories of heating appliances.

We include excerpts from UMC tables forth with additional commentary to assistance in sizing metal or masonry chimneys co-ordinate to chimney diameter, height, materials, and the input BTUH of the appliance(southward) to be vented.

We also provide an Commodity Alphabetize for this topic, or you can endeavor the page top or bottom SEARCH BOX every bit a quick way to find information you need.

Sizing of Metal & Masonry Chimney Flues, Flues, Vents - Category I Draft Hood and Fan Assisted Appliances

Sentinel out: Bank check with your local building lawmaking officials for local building code requirements when designing, building, or installing chimneys and vents.

NFPA 1992 (7.5.3) states that draft hood appliances, Category I appliances and other appliances that employ Type B vents must have a

chimney flue area not less than the area of the largest vent outlet plus l% of the area of the boosted flue outlet.

The 1992 GAMA vent sizing tables for single-wall metal vent connectors attached to a tile lined masonry chimney uses Table 8. The outcome of those calculation using a 38,000 BTU h2o heater with a 3" draft hood and a 37,500 BTU banality with a four" draft hood connected to a 20' high chimney is to apply a common flue with an expanse of 28 square inches or a 6" flue vs a 5" flue in the previous examples.

Details well-nigh factors that go into calculating the size of a chimney or flue are discussed separately at CHIMNEY SIZE FACTORS.

Tables of Chimney, Flue, or Vent Size Requirements vs. BTUs of Appliances being Vented

A Guide to Chimney Sizing Tables for Venting Heating Appliances: Which Chimney Sizing Table to Use

Here is a quick guide to the UMC's chimney sizing & BTUH venting capacity tables when sizing a metal or masonry chimney diameter to match the total input BTUH of the heating appliances (boiler, furnace, water heater) being vented. Note that different chimney sizes are required for venting fireplaces and woodstoves.

Masonry fireplace chimney size requirements are at FIREPLACES & HEARTHS.

Chimney Blazon	Number of Appliances to be Vented
Metal B-Vent Chimney (Vent) Type of Flue Vent Connector:ⁱ	Single Apparatus	Multiple Appliances
	Which Chimney Flue / Vent Sizing Table to Use
Single Wall Flue Vent Connector	Table C-9-A	Table C-nine-E (ii part table)
Double Wall B-vent Flue Vent Connector¹	Tabular array C-9-B	Table C-9-D (two part tabular array)
Masonry Chimney ⁱⁱ
Single Wall Flue Vent Connector	Table C-9-C	Tabular array C-nine-F (two part tabular array)
Minimum Input BTUH, Single apparatus, natural gas, B-vent connector vs chimney height, size, & outdoor temperature	504.2(6)

Notes to the Table Higher up

1. A flue vent connector is the horizontal/sloped metal pipage connecting the heating appliance to the entry point of the chimney. Flue vent connectors and their materials, sizing requirements, & burn down clearances are

at FLUE VENT CONNECTORS, HEATING EQUIPMENT

At double-wall B-vent chimneys the flue vent connector betwixt the appliance and the chimney entry point may be unmarried-wall metallic flue vent connector or it may exist a double-wall Type-B flue vent material.

2. At most masonry chimneys the flue vent connector or "stackpipe" or "smokepipe" is single wall metallic, though for fire clearance needs it may be amended to use sections of insulated metal chimneys.

See CHIMNEY Cantankerous Section SHAPE Furnishings for the effects of square vs round chimney sectional areas

Types of metal chimneys and their properties and fire clearances are

at METAL CHIMNEYS & FLUES.

Tabular array C-nine-A (Excerpts): Unmarried Appliance Venting, B-Vent Chimney Capacities for Venting a Unmarried Heating Appliance where a Single Wall Metallic Flue Vent Connector is Used Betwixt the Appliance and the Chimney

BTU Color Coding Note: in the tables beneath we use colors to signal where an example-approximate appliance BTUH vent chapters rating falls across various chimney parameter combinations. The Gray colour indicates that this chimney height and diameter combination cannot exist used.

Total Chimney/Vent Elevation (ft)	Lateral (horizontal) Run (ft)	Table of B-Vent Diameter (inches) for a Single Appliance Chimney
		3 in.	four in.	5 in.	6 in.	7 in.	8 in.	Comments
		Maximum (single) Appliance BTU Input Rating (thousands of BTUs)
6 ft.	0	39	lxx	116	170	232	312
	two	31	55	94	141	194	260
	v	28	51	88	128	177	242
8 ft	0	42	76	126	185	252	340
	2	32	61	102	154	210	284
	5	29	56	95	141	194	264
	10		49	86	131	180	250
10 ft	0	45	84	138	202	279	372
	2	35	67	111	168	233	311
	v	32	61	104	153	215	289
	10		54	94	143	200	274
	15			84	130	186	258
15 ft.	0	49	91	151	223	312	420
	2	39	72	122	186	260	350
	5		67	110	170	240	325
	ten			103	158	223	308
	15				144	207	291
	20					195	273
20 ft.		101	163	252	342	470	770
		80	136	210	286	392	641
			123	192	264	364	610
				178	246	345	571
				163	228	326	550
						306	525
xxx ft.			183	276	384	529	878
				230	320	441	730
				210	296	410	694
					274	388	656
						366	625
						344	596
							540

Tabular array C-nine-B (Excerpts): Single Apparatus Venting, B-Vent Chimney Capacities for Venting a Unmarried Heating Appliance where a Double-Wall B-Vent Flue Vent Connector is Used Betwixt the Appliance and the Chimney

See FLUE SIZE SPECIFICATIONS_TABLE_C_9_B

Tabular array C-9-C (Excerpts): Single Appliance Venting, BTU Capacity of Masonry Chimneys where a Single Wall Metal Flue Vent Connector is Used Between the Appliance and the Chimney

Come across FLUE SIZE SPECIFICATIONS_TABLE_C_9_C

Table C-9-D (Excerpts): Multiple Appliance BTU Vent Chapters of Blazon B Double-Wall Vents where a Double Wall Metallic B-Flue Vent Connector is Used Between the Appliance and the Chimney

Meet CHIMNEY FLUE SIZE SPECIFICATIONS_TABLE_C_9_D

Spotter out: the first portion of Table C-9-D specifies the maximum input BTUH chapters of whatsoever individual heating appliance that is to exist vented forth with other appliances out through a unmarried chimney. An additional table, the Continuation of C-9-D gives the chimney specifications for the full input BTUH of all of the appliances, combined.

Table C-9-East (Excerpts) Multi-Apparatus BTUH Venting Capacity of Double-Wall B-Vent Chimneys where a single-wall metal vent connector is used between the appliances and the chimney

This two-part tabular array gives the chimney specifications for the total input BTUH of all of the appliances combined and joined into a unmarried vent when the flue is a Type-B double wall metal chimney and when the flue vent connector (between the appliance and the chimney entry signal) is a single wall metal component.

See CHIMNEY FLUE SIZE SPECIFICATIONS_TABLE_C_9_E

Table C-9-F (Excerpts) Multi-Apparatus BTUH Venting Capacity of MASONRY CHIMNEYS where a single-wall metal vent connector is used between the appliances and the chimney

This ii-office table gives the chimney specifications for the total input BTUH of all of the appliances combined and joined into a unmarried vent when the flue is a masonry chimney and when the flue vent connector (between the apparatus and the chimney entry point) is a single wall metal component.

Come across CHIMNEY FLUE SIZE SPECIFICATIONS Tabular array C-9-F

Table 504.two(half-dozen) Outside Masonry Chimneys Venting Natural Gas Appliances

See CHIMNEY FLUE SIZE SPECIFICATIONS Tabular array 504.2

Details About Chimney Cross Exclusive Areas and Effects on Venting Capacity of Masonry Chimneys - Translating Rectangular Chimney Flues to Circular Flue Equivalents

The UMC Appendix C Table C9-G, "Masonry Chimney Liner Dimensions with Circular Equivalents" translates foursquare or rectangular chimney flue inside dimensions into an equivalent "round" flue diameter and into equivalent foursquare inches of venting capacity.

Why does this translation matter? The venting capacity of a rectangular or foursquare masonry flue, if translated direct into actual or measured square inches of cross section, is less than a round chimney flue of the same square inches of venting capacity.

For instance an 8" 10 viii" foursquare nominal clay chimney flue tile liner has inside dimensions of vi 3/iv" x 6 3/four". Just muliplying these dimensions together (6.75 x 6.75) = 45.56 sq.in. Just chimney experts and draft measurements prove that in a rectangular flue not all of the cantankerous-sectional area is as effective in developing typhoon. The effective square inches of venting area, translated to an equivalent circular flue, would be less - or aboutd 42.7 square inches.

So when calculating the venting capacity of a square or rectangular clay chimney flue tile or liner past looking at its cross department, nosotros utilize the UMC's Table C9-G of "circular chimney flue equivalents" to become the effective chimney flue vent cross exclusive expanse earlier nosotros enter the masonry chimney BTUH venting chapters tables 6-9-C (single wall flue vent connectors and single heating appliances) or 6-9-F (single wall flue vent connectors and multiple appliances).

[Notation: pending description, nosotros have not provided excerpts of Table C-9-G because, bluntly, some of its data is confusing. - Ed.]

Watch out: Check with your local edifice code officials for local edifice code requirements when designing, building, or installing chimneys and vents.

Reader Comments & Q&A

[Click to enlarge any image]

Mary:

Cheers for a helpful question: how do I go the required size for the flue vent connector that vents ii or more heating appliances into my masonry chimney?

To become the correct chimney size (or to see the limitations of what your 8x8" chimney can maybe vent in BTUs,

come across CHIMNEY FLUE SIZE SPECIFICATIONS Tabular array C-9-F

To avert confusion, nosotros telephone call the vertical venting system the "chimney"

The (roughly-horizontal but actually sloped "upwards") metal "pipe" that connects one or more heating appliances to the entry thimble in the masonry chimney is chosen a

flue vent connector - typically unmarried wall metal, 24-judge steel -

Discover that ultimately the maximum size of your masonry chimney is 8x8 or 64 sq.in.

The size of your flue vent connector or "flue pipe" needed depends on several variables including:

- the size and input BTUH of each of the appliances beingness vented

- the size of the flue-vent connector on each of those appliances (this will exist the bare minimum and is typically the size of the vertical flue vent connector betwixt the appliance and the horizontal flue vent connector that continues on into the chimney thimble or point of entry)

- The length of horizontal run

- The gradient of horizontal run

To get the right flue vent connector size when venting multiple appliances into a single chimney or flue

see CHIMNEY FLUE SIZE SPECIFICATIONS_TABLE_C_9_E

Lookout out: also Important are the heating appliance manufacturer's installation instructions - follow those

Lookout out: your 8x8" clay flue tiles forming the bodily masonry chimney flue besides set up a limit on the total input BTUH that the chimney itself can handle - again affected past height and other factors.

More than helpful chimney and flue vent connector sizing articles are suggested above on this page and in the ARTICLE INDEX

Herewith I adhere an excerpt from CHIMNEY FLUE SIZE SPECIFICATIONS TABLE C-nine-F that gives sizing for flue vent connectors.

first question-what is the proper gauge for this application and secondly, what size duct do i utilise as common pipage later on wye junction?

when 2 gas appliances are vented through category 1 single wall galv. duct to a 8x8 dirt tile flue

i take 2 questions.

Thanks for the follow-upwardly, Ron.

Regarding the question below, the oil tech said that it should be OK for our setup. He will come out at some point to arrange the draft if needed. Thank you for your help!

Yes, Flue, going to a smaller diameter primary flue in a chimney may reduce the draft. The total result depends on several variables including chimney height, ambient temperature range, and oil burner/heater input BTUH and burner adjustments.

At the very to the lowest degree you need to accept a trained service technician inspect, mensurate, and if necessary adjust the draft and draft regulator for your sometime Weil Mclain heater. She bank check combustion air and volition measure draft over the fire, draft in the breech, stack temperature and CO2 or O2. With those measurements she can determine if the burner is operating properly.

If, after adjusting the typhoon regulator for your heater she cannot obtain sufficient typhoon for your heater it might be necessary to add a draft inducer fan.

Get this inspecting and testing done soon since leaving a heater working improperly (if it is) can atomic number 82 to unsafe operation.

Let me know what the tech finds.

I have a 30 twelvemonth old oil furnace (Weil Mclain) with a vii inch flue going into chimney. A company installed a new galvanized steel chimney liner with a 6 in diameter and connected them with a reducer. Will this reduction touch on anything?

Rais stove LPG versus LNG gas orifices cited & discussed at Inspectapedia.com Anon I'm sure at that place are a number of installation, adjustment or maintenance defects that can cause a propane stove to over-fire, and that there are specific defects and serious safety issues that are specific stove blazon, brand, and model dependent.

Among the obvious are

Improper gas burner orifices - set perhaps for the wrong fuel, such every bit mixing LPG and Natural gas set up-upward procedures ( this could exist your trouble), or an improper pressure regulator setting, or improper burner adjustment.
Improper ceramic log positioning could also cause improper gas flame.
Watch out: ANY improper gas burner operation is unsafe.

FIRE OR EXPLOSION Run a risk. Failure to follow condom warnings exactly could result in serious injury, death, or property damage.

For other readers, Rais is a Danish manufacturer of woods and gas burning stoves. https://united states of america.rais.com/almost-rais.html is the company's United states of america site and the company's main gas fireplace website: https://www.rais.com/en/gas-fireplaces

Shown below, a Rais QTEE-Ii gas stove for which you can read the RAIS QTEE GAS STOVE MANUAL [PDF] at

Manual excerpts:

The stove is supplied configured for natural gas or Propane gas only tin be converted. The conversion must only be carried out past an authorised gas engineer. Utilise conversion kit with commodity number 3713595 NG to LPG or 3713596 LPG to NG. The conversion kit's contains 4 new nozzles.

The stove is preset to provide the correct corporeality of rut (kW) as described nether specifications. There is no demand for further adjustment.
"Inlet pressure" and "Burner pressure level" must ALWAYS be measured. - additional instructions are on p. 53

Watch out: if this is not your Rais stove model then of course you demand to follow the instructions for your specific stove.

what cause a directly vent Rais propane stove to over burn down

Anon

Ratio of fireplace opening Dimension to chimney flue size

A reasonable rule of thumb giveing the ratio of fireplace opening size to the cross-sectional surface area of the fireplace flue vent opening is 10 to i.

Then just practise the calculation of square inches of your fireplace opening and take i 10th of that and yous'll be in the correct ballpark for the chimney flue dinensions.

Keep in heed that a number of other important factors will bear upon the chimney draft and volition make your fireplace piece of work well or notation such every bit availability of outdoor combustion air and the proper cake of the fireplace itself besides every bit the throat and chimney to follow the description of the Rumford fireplace figured out revolutionary times. If you search this website for a Rumford fireplace you'll detect more details.

we have a fireplace opening 5feet wide and xxx inches high . what size influenza do we need

Adept question, Charles. I don't know. Bold that the connectedness can be made safely between the dissimilar chimney diameters and materials, and that the above-roof meridian is just a few feet, that may be ok. My business organization is that changes in diameter of a flue have impact on the draft. 3" venting into 6" is quite an increase. I'd want to know

1. what's beingness vented and is the 3" vent adequate in the first identify. Too small OR too large a flue tin brand venting difficult and even dangerous

2. what are the vertical dimension involved and what will be the draft bear on.

I would give a call to the manufacturer of the metal flue you're using to ask their stance.

It may too be possible to simply make some conscientious typhoon measurement nether various atmospheric condition (heater in use, diverse outdoor & flue temperatures & wind conditions) that can back up the blueprint.

Tin can a iii" metal flue exhaust into a 6" flue at the roof?

Jerry, I can't say, merely you might discover the information you need in your woodstove'southward installation transmission where the manufacturer will specify the minimum flue size for your particular stove.

I'm going to install a clay lined brick chimney in my two story habitation for a forest called-for stove! Chimney will be 25'-30' in height when completed. What would a correct clay flu liner size should I utilise?

Question: chimney size vs. btuh ratings

(Aug 30, 2011) david said:
what if you had a 4" furnace outlet and 2 3" outlets. is it the same formula or do you go off of actual btus

Reply:

David I don't quite understand the question. Simply in general the chimney venting requirements are set by the fuel type and the BTU rating of the appliance.

Question: standard chimney heights

(Sept 9, 2011) Graham said:
What is the standard superlative above a tiled roof to the top of chimney ?

Respond:

Graham please see CHIMNEY Top & CLEARANCE Code

Question: reduce furnace flue vent connector size below furnace outlet size?

(October 13, 2012) Brent said:
I have a single 2650 sq ft home that was in one case subdivided, 1 side had a 133,000 btu oil boiler and I have a 115,000 gas banality. I want to purchase a new boiler to heat both sides which I have zoned.

My question is that my looad adding calls for a 136,000 btu furnace, in this range I'm looking at a 142,000 furnace.

My chimney (30 ft tall) has a stainless 6 " liner but the new furnace outlet is 7"

Tin I safely reduce the outlet from seven" to 6" ? I also take a gas hot water heater on the aforementioned flue in a "y" connection.

Brent

Reply:

Question: ok to share chimney flue if heaters don't run at the same time?

(January 27, 2014) (mod) said:
Bill, I am re-posting your question without the imbedded hyperlink - our arrangement doesn't permit links in comments for reasons of security.

"My coal boiler and oil boiler vent into the same chimney. I never use both at the same time. The chimney is about 30 feet high. The stove pipes are 6" single wall.

The coal boiler enters below the oil boiler and on the opposite side of the chimney. There is no rise to the coal boiler's stove pipe, it enters direct into the chimney and runs slightly down hill. I'm called-for bituminous coal get smoke billowing out the door when I open up it even though I accept lots of draft. I'm thinking information technology may be due to the way it has been piped causing a limitation in flow.

Information technology looks to me similar the coal boiler's input was changed when the 6" square clay liner was installed. There is a knock out cemented over that I tin can utilise, I would simply have to cut an opening into the clay liner.

The coal boiler would then enter nearly half dozen" to a higher place the oil banality. I don't accept whatever room to go higher. This would put nearly 16" of rise on the coal boiler's fume pipe. I stuck 2 sometime elbows in to prove to myself that I accept room to rearrange the piping, you can see them in the pic.
Do you think this alternate piping might make an improvement? "

Before thinking well-nigh sharing a chimney flue - generally prohibited as a safety concern but permitted in some jurisdictions, peculiarly with gas and oil fuels provided proper venting organisation - I'd check with your local building department about what they let. Permission may also depend on the chimney type and design.

Condom issues aside for a moment in that location can be draft control and operating difficulties - whatever solution has to forbid automated draft from i appliance from fouling upward the other.

Reply:

You might observe draft conflicts (can't optimize for both appliances), fire hazards (ane heater igniting deposits from the other), code violations, and fire spread safety hazards.

Question: shared Y connection for chimney connection?

(April 2, 2014) sal avanzato said:
my chimeney [30ft tall] has8"x13"terracotta flue liner with 7" round terracotta crock going into the flue liner. tin I safely hook upwardly gas boiler 175000 btu and water heater 75000 btu into 7" round crock on the same flue in a"Y"connection

Reply:

Sal,

You have 175,000 + 75,000 BTUH = 250,000 BTUH venting required

You don't give the horizontal distances of your 7" flue vent connector(southward) between the appliances and the chimney, nor do you say if the appliances are natural typhoon or forced draft, then we don't have the total reply to your question, nor am I confident commenting on "safety" for an unknown system since a fault can be fatal.

At the start of the article above we give some help choosing which tables to use to answer chimney questions.

If we are venting multiple appliances into a single chimney flue we use Table C-9-F
(two part tabular array) in the commodity above.

Your chimney cross department surface area is 8 x xiii" = 104 sq.in. Your chimney height is xxx ft. (which gives adept draft).

But an important limit here is the input 7" flue diameter. And some jurisdictions (see Seattle WA code for example) limit the horizontal run distance (to near 10 ft. for vii" flue vent connectors OR you lot have to reduce the assumed venting chapters of the arrangement)

There are also assumptions well-nigh outdoor temperatures that affect the chimney typhoon conditions.

Not shown anyway in our table (I'll add some information) is that per the AGA NFPA code, if I assume the horizontal flue vent connector distance is 10 anxiety or less and the chimney meridian is thirty feet,

bold an outdoor temperature range of 27 to 36 degF or higher (colder ranges give better draft once the chimney has heated-up so this is a cautious assumption) your 104 sq. in. chimney (assuming that's *internal* area, falls between 2 standards:

a 78 sq. in. xxx foot masonry chimney in this outdoor temperature range can vent 445,000 input BTUH
a 113 sq. in. 30 foot masonry chimney in this temperature range tin vent 485,000 input BTUH.

And then equally your chimney is in between those two and even the smaller internal size chimney can vent more BTUH than you are connecting the chimney itself meets the standards every bit I read them. (Check with your local building code officials for safety and local code compliance and of course check that the chimney is in fact intact, not leaking, damaged, blocked, that there is safe combustion air etc. or ALL of this give-and-take would be nonsense since there could be very unsafe conditions, fifty-fifty fatal ones, present).

Adding about outdoor chimney temperatures vs. working chimney meridian, there is a second concern that in cold conditions it is more than hard to get typhoon working in a taller outside masonry chimney since the flue gas from the appliance has to overcome the weight of a tall column of common cold air.

Question: moving a wood heater insert into a shop

13 Jan 2015 Steve Said:

I took a 20 year old woods heater insert out of my fire place. Im putting it in my shop.The heater does non have a pipage neckband .Information technology has a 7 x viii inch opening where i can put a collar.I dont know what size to put 6 inch or 8 inch? Within measurements of heater are 24 inch wide past nineteen inch deep by 18 inch summit 24x19x18 inside

Elevation from proposed collar to ceiling 13feet 4inches through metal roof and insulation 2inches roof has a 1 by 12 pitch.. What size stove pipe practise i apply and why

Reply:

Steve,

Generally a larger vent is functional and prophylactic as long as the chimney size and peak are not and then large that the heating apparatus won't develop adequate draft. It's not just stove pipe size y'all need to consider, but proper fire-rating of the flue or chimney materials, clearances from combustibles, cleanout access and code.

Spotter out: But continue in mind that nigh likely you need to obtain a building permit and inspections for installing any new heater anywhere - don't view that as a stumbling block but rather equally an extra inspection that might help avoid a burn.

...

Keep reading at CHIMNEY FLUE SIZE SPECIFICATIONS_TABLE_C_9_B or select a topic from the closely-related articles below, or meet the complete Commodity Index.

Or encounter these

Suggested citation for this web page

CHIMNEY FLUE SIZE SPECIFICATIONS at AuditApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

Alphabetize to RELATED ARTICLES: ARTICLE Index to CHIMNEYS & FLUES

Or use the SEARCH BOX constitute below to Ask a Question or Search InspectApedia

...

Inquire a Question or Search InspectApedia

Try the search box simply beneath, or if you lot prefer, post a question or comment in the Comments box below and we will answer promptly.

Search the InspectApedia website

Note: appearance of your Comment below may exist delayed: if your comment contains an image, web link, or text that looks to the software as if information technology might be a web link, your posting will appear subsequently it has been approved by a moderator. Apologies for the filibuster.

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher InspectApedia.com - Daniel Friedman