Our technical support personnel have identified the following questions about gas venting as the ones most frequently asked. The answers are designed to help you better understand the nature of this type of vent, but we recommend that you consult the installation instructions for the manufacturer of your vent, the listing by Underwriters Laboratories and your own local building codes.

1. Are the AMPCO® VSI products listed for positive pressure?
2. Do the AMPCO® products have captive nuts and bolts?
3. Are AMPCO® systems UL Listed?
4. Can VSI chimney product be used to vent any appliance?
5. Can AMPCO®, VSI products be used to vent Category II, III or IV condensing appliances?
6. Is it difficult to design and quote a system without calling AMPCO®?
7. Should an AMPCO® representative know how and be expected to quote certain jobs?
8. Why does AMPCO® insist on making a drawing when all we want is a quotation?
9. How long does it take to receive a quote?
10. What is the quickest ship date I can get when ordering an AMPCO® system?
11. Can an appliance listed for use with Type B Gas Vent, and a positive pressure rated appliance be connected to the same vent system?
12. Why do AMPCO® systems require expansion joints?
13. Can an expansion joint (EJ) be used as a fixed adjustable length (FAL)?
14. How often are supports required?
15. How important are support locations?
16. Is drywall or sheet rock considered a non-combustible material?
17. Why do the AMPCO® engineers ask if the roof is combustible?
18. Can a chimney system be smaller than the appliance outlet?
19. Does the use of a Briedert cap on an AMPCO® chimney really void the UL Listing?
20. What is the purpose of a stack drain section?
21. When is the AMPCO® sizing program used, and when are the GAMA or National Fuel Gas Code sizing tables used?

1. Are the AMPCO® VSI products listed for positive pressure?
All of the AMPCO® VSI product lines have passed the UL 103 Positive Pressure Applications Test (Sec. 22A). This test qualifies these products to be used on positive pressure systems. If manufacturers do not label their product indicating a rated maximum internal pressure when used in positive pressure applications, they are not suitable or listed to be used as a positive pressure vent or chimney. At this time there are very few manufacturers that have passed this mandatory test for positive pressure applications.

2. Do the AMPCO® products have captive nuts and bolts?
Yes, this unique feature eliminates loose nuts and bolts, and therefore, allows the entire system to be installed while wearing gloves. For years AMPCO® was the only manufacturer to use captive fasteners; however, at least one competitor is now using this labor saving feature.

3. Are AMPCO® systems UL Listed?
AMPCO VSI-II, IVSI-1, IVSI-2 and IVSI-4 are UL listed in the United States and Canada as Building Heating Appliance Chimneys for venting gas, liquid and solid fuel appliances at a temperature not exceeding 1000º F continuous, 1400º F Chimney for venting gas, liquid and solid fuel appliances at a temperature not exceeding 1400º F continuous and as Grease Ducts For Restaurant Cooking Appliances. Single wall VSI-I is UL listed as a Grease Duct For Restaurant Cooking Appliances and the materials and construction comply with most code requirements for chimney connectors and masonry chimney liners.

4. Can VSI chimney product be used to vent any appliance?
There are some appliances that should not use VSI products. VSI products are suitable for boilers, generators, grease duct, certain fume hood applications, some incinerators, ovens, gas-fired chillers, etc. Consult the AMPCO® engineers when there is any question.

5. Can AMPCO®, VSI products be used to vent Category II, III or IV condensing appliances?
Category II, III, and IV appliances must use a Listed Special Gas Vent or materials as listed and specified by the appliance manufacturer. AL29-4C stainless steel is the only metallic material that has been UL Listed and found acceptable for this application. Although we could manufacture our products with this material, AMPCO® has elected to become a distributor for Heat Fab. Heat Fab products are specifically designed and UL Listed to UL 1738 Venting Systems For Gas-Burning Appliances, Categories II, III, IV. Call your AMPCO® applications engineers for more information.

6. Is it difficult to design and quote a system without calling AMPCO®?
With the use of the AMPCO® Installation Instructions and the correct price sheet, it is relatively easy to design a simple system and calculate the cost. However, it is easy to overlook essential components such as the connection to the appliance, supports for the system, expansion and drainage.

7. Should an AMPCO® representative know how and be expected to quote certain jobs?
Most contractors feel much more comfortable if our representatives have the ability to quickly quote small one or two appliance installations. For larger jobs, the AMPCO® application engineers should be contacted to size, design and accurately quote the job, but the contractor’s confidence in the AMPCO® representative sells more jobs.

8. Why does AMPCO® insist on making a drawing when all we want is a quotation?
An accurate drawing is the best way to insure that AMPCO has correctly interpreted the specifications we received. It is also the best document to eliminate any misunderstanding and make the contractor, engineer or owner aware of what was really quoted.

9. How long does it take to receive a quote?
The average lead time for a quotation is five working days. A timely quote can be expected only after AMPCO® application engineers receive accurate job details and specifications, including site plans, as well as, information on all connected appliances. Occasionally, a complex, unusual or peek season job may also extend the lead time of an accurate quotation.

10. What is the quickest ship date I can get when ordering an AMPCO® system?
For emergencies and customer convenience, AMPCO® offers a special five day, build and quick-ship alternative. Check with the AMPCO® commercial product specialists for details.

11. Can an appliance listed for use with Type B Gas Vent, and a positive pressure rated appliance be connected to the same vent system?
Type B Gas Vent should only be used in negative pressure applications. AMPCO® engineers can design a system to maintain a negative operating pressure allowing a Type B Gas Vent appliance to be connected downstream from the positive pressure appliance. Always consult AMPCO’s product specialists prior to designing any mixed rating systems.

12. Why do AMPCO® systems require expansion joints?
Without expansion joints, the expansion characteristics of a VSI system inner wall are similar to a solid rigid tube. The inner wall is also the primary connection and load bearing member of the system. Therefore, to absorb expansion induced by flue gas temperatures, an expansion joint or bellows joint must usually be installed between any two fixed points. A fixed point is any VSI Support Assembly or the appliance. Expansion joints (EJ) are recommended for boilers, while bellows joints (BJ) are required for generators. The approximate expansion of the inner wall is one inch per 100º F per l00 feet. Consult the installation instructions for details.

13. Can an expansion joint (EJ) be used as a fixed adjustable length (FAL)?
Often an EJ can take the place of an FAL but, an FAL can never take the place of an EJ. The function of the fixed adjustable length is to make a special length of straight pipe which becomes a fixed length once the adjustment is made. An expansion joint remains variable in length to compensate for expansion within the system.

14. How often are supports required?
Most required supporting points are obvious, such as at the base of a vertical run. However, you should also consider a support any time there is a change of direction, either upstream or downstream of an expansion or bellows joint and at any point that must anchor the system to the building. Refer to the installation instructions for minimum requirements.

15. How important are support locations?
Properly installed structural steel supports are extremely important. The higher the flue gas temperatures the more critical expansion compensation becomes. Improper supports or expansion calculations may cause structural failures.

16. Is drywall or sheet rock considered a non-combustible material?
Although sheet rock is a fire rated material, the NFPA 54, 97 and 211 Standard’s definition of “combustible material” is intended to include sheet rock as a combustible material. Alternate non-combustible materials are available, and should be considered when designing a chase or creating non-combustible surfaces.

17. Why do the AMPCO® engineers ask if the roof is combustible?
A Roof Penetration must be used to penetrate a combustible roof, while a less expensive Tall Cone Flashing can often be considered if the roof is non-combustible and the AMPCO® system is not enclosed. Consult the AMPCO® VSI Installation Instructions for more information.

18. Can a chimney system be smaller than the appliance outlet?
There are occasional situations that would allow this, such as tall vertical runs or fan assisted systems. Contact the AMPCO® product specialists for their recommendations.

19. Does the use of a Briedert cap on an AMPCO chimney really void the UL Listing?
All components used to make a system must be manufactured by the company and within the facility that has been UL Listed for the manufacture of that product. Therefore, all parts and pieces manufactured by anyone other than AMPCO®, even if the parts are UL Listed by a competitor, could void the UL Listing.

20. What is the purpose of a stack drain section?
A stack drain section is designed to route condensation and/or rain water to a drain, and therefore, prevent the contaminates from entering the appliance.

21. When is the AMPCO® sizing program used, and when are the GAMA or National Fuel Gas Code sizing tables used?
The AMPCO® computerized sizing program is used to calculate the chimney size for a positive pressure system. The sizing tables are used to calculate chimney size for gas fired Category I appliances only.

Note:
This is not intended to take the place of the factory furnished installation instructions, nor local Building or Fire Codes. Refer to the installation instructions for more complete details. For additional assistance, contact the AMPCO® Product Specialists at (800) 624-8642.