Hot water (hydronic) & steam boiler installation clearances & fire clearances:
What are the required clearance distances around a heating boiler: here we provide a table of recommended working space and fire clearances for oil and gas fired heating boilers.
This article series answers just about any question about hot water or steam heating system troubleshooting, inspection, diagnosis, and repairs in residential buildings and homes. If your heat is by forced warm air use the on page search box for FURNACE CLEARANCES.
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In most general terms, and using the model IRC International Residential Code, you are required to provide
More of those sources are given at the end of this article.
Photo above: a terrible steam boiler installation that we inspected in Gramercy Park, New York City.
[Click to enlarge any image]
Below: example of minimum boiler clearance spaces and working space, adapted from
the BUDERUS SSB85 BOILER IO MANUAL [PDF] as an example.
Watch out: the specific boiler clearances for your heating boiler will vary; check your manufacturer's IO manual. For example, Buderus specifies 40-inches in front of the boiler - that's more than is specified in the IRC cited below.
All of the model building codes agree that when the manufacturer's specifications are more demanding, those are what shall be followed.
Appliances shall be accessible for inspection, service, repair and replacement without removing permanent construction, other appliances, or any other piping or ducts not connected to the appliance being inspected, serviced, repaired or replaced.
A level working space at least 30 inches deep and 30 inches wide (762 mm by 762 mm) shall be provided in front of the control side to service an appliance.
Installation of room heaters shall be permitted with at least an 18-inch (457 mm) working space.
A platform shall not be required for room heaters.
Below we excerpt from the New York City boiler code as a model and general boiler clearance spacing guideline, followed by other model and code or manufacturer's requirements citations.
However, the board may adopt rules prescribing fire protective measures and minimum spaces for and around furnaces, boilers or installations of fuel oil burning equipment. Such rules shall be adopted as the board may deem necessary and proper for the safety, protection and welfare of the city and its inhabitants.
If the board shall adopt such rules, the provisions of paragraph one, two and four of this subdivision shall not apply to such furnaces, boilers or installations of fuel oil burning equipment as are included within the purview of such rules.
- Source: NYC Boiler Code cited below
Clearances shall be maintained around boilers, generators, heaters, tanks and related equipment and appliances so as to permit inspection, servicing, repair, replacement and visibility of all gauges.
Where boilers are installed or replaced, clearance shall be provided to allow access for inspection, maintenance and repair. Passageways around all sides of boilers shall have an unobstructed width of not less than 18 inches (457 mm), unless otherwise approved.
Clearances from the tops of boilers to the ceiling or other overhead obstruction shall be in accordance with Table 1004.3.1. [adapted below]
Boiler Top Clearance Distances |
|
Boiler Type | Clearance from |
All boilers with manholes on top of the boiler except where a greater clearance is required in this table. |
3 ft |
All boilers without manholes on top of the boiler except high-pressure steam boilers and where a greater clearance is required in this table. |
2 |
High-pressure steam boilers with steam generating capacity not exceeding 5,000 pounds per hour. |
3 |
High-pressure steam boilers with steam generating capacity exceeding 5,000 pounds per hour. |
7 |
High-pressure steam boilers having heating surface not exceeding 1,000 square feet. |
3 |
High-pressure steam boilers having heating surface in excess of 1,000 square feet. |
7 |
High-pressure steam boilers with input not exceeding 5,000,000 Btu/h. |
3 |
High-pressure steam boilers with input in excess of 5,000,000 Btu/h. |
7 |
Steam-heating boilers and hot water-heating boilers with input exceeding 5,000,000 Btu/h. |
3 |
Steam-heating boilers exceeding 5,000 pounds of steam per hour. |
3 |
Steam-heating boilers and hot water-heating boilers having heating surface exceeding 1,000 square feet. |
3 |
Equipment shall be set or mounted on a level base capable of supporting and distributing the weight contained thereon. Boilers, tanks and equipment shall be secured in accordance with the manufacturer's installation instructions.
Boilers shall be mounted on floors of non-combustible construction, unless listed for mounting on combustible flooring.
Boiler rooms and enclosures and access thereto shall comply with the International Building Code and Chapter 3 of this code. Boiler rooms shall be equipped with a floor drain or other approved means for disposing of liquid waste.
Below we cite New York Building Code section 4-6.4 as an example of clearance for boilers in a new space not previously used as a boiler room:
The clearance between any component on the side or rear of a boiler and any wall or partition of the building in which it is installed shall be not less than 24 inches where the rated gross capacity is less than 5,000,000 Btu per hour.
Where the rated gross capacity exceeds 5,000,000 Btu per hour, the clearance to any unprotected combustible construction shall be not less than 36 inches.
The clearance between any component of the boiler and any other boiler or equipment shall be not less than 24 inches.
The clearance from the front wall or head or heat generating apparatus of the boiler, whichever is closer to the building wall partition or other equipment, shall be not less than four feet where the rated gross capacity is less than 5,000,000 Btu per hour.
Where the rated gross capacity exceeds 5,000,000 Btu per hour, such clearance shall be not less than six feet.
When working platforms, required for boilers where the distance from the floor to the top of the boiler or boiler setting exceeds eight feet, are installed on top of a boiler for operating or maintenance purposes, the clearance from the working surface of such platform to the lowest point of any overhead structure shall be not less than seven feet.
Source:
[in process, meanwhile see the clearance distances specified above on this page; reader contributions are invited. Use the page top or bottom CONTACT link or post suggestions as a comment at the bottom of this page]
Oil Fired Boiler Venting
Following is excerpted from the New York City Boiler code cited below.
1. (a) The minimum distance between any smoke pipe or breeching and any combustible material or construction shall be eighteen inches in the case of low temperature heating devices and thirty-six inches for medium or high temperature heating devices, except that, when such combustible material is protected with at least two inches of asbestos or in some other approved manner, such clearance may be reduced one-half.
(b) The board may adopt rules prescribing fire protective measures and minimum distances between smoke pipes or breechings and any combustible materials or construction.
Such rules shall be adopted as the board may deem necessary and proper for the safety, protection and welfare of the city and its inhabitants. If the board shall adopt such rules, the provisions of item a of paragraph one of this subdivision shall not apply to such furnaces, boilers or installations of fuel oil burning equipment as are included within the purview of such rules.
2. It shall be unlawful to pass any smoke pipe through any floor. (11.3.9.7).
Smoke pipes from low temperature heating devices, passing through combustible partitions, shall be guarded by a double metal ventilating thimble twelve inches larger in diameter than the pipe, or by a metal tube built in brick work or other approved fire resistive materials, at least eight inches thick on all sides of the tube .
- Source: NYC Boiler Code cited below
There are several gas or oil fired heating boiler clearance distance types:
Typical Minimum Clearance Distances for Gas Boilers |
||
Clearance Topic | Clearance Distance | Comment / Reference |
General boiler clearances & working space | ||
Must meet all manufacturer's clearance specifications | Various | See I&O Manual for the specific brand & model heater |
Must meet all local & national building, fire, electrical, fuel-gas codes | Check with local code officials | |
Service / working space - front | 24" | Notes 1, 2 |
Service / working space - other sides, panels | Note 2 | |
Combustion air openings & nearest closed panel or door | 3" | Note 3, do not block air flow into combustion air intake |
Combustion air & ventilation openings | not blocked by anything, including snow | |
Space for addition of cooling coil | Note 4 | |
Attic installations | Notes 6, 7, service access to front, limited framing contact, may be suspended | |
Burner & ignition above garage floor | 18" | Note 5 |
Crawl space installations | Note 8 |
...
Clearance Topic | Clearance Distance | Comment / Reference |
Gas Boiler Clearance to combustibles, model dependent | ||
Sides to combustible surface | 0 - 1" | Note 1 |
Front to combustible surface | 3 - 18" | Note 1 |
Top to combustible surface | 1" | Note 1 |
Flue, condensing boiler, plastic vent | 0" | Notes 1, 10. |
Flue through masonry chimney w/ other appliances, stainless steel type 29-4C | Note 11 | |
Condensate drain elevation | 4-6" | Note 9 |
Attic installation of horizontal unit | Note 7 |
1. AMERICAN STANDARD GAS FURNACE INSTALLATION MANUAL [PDF] (2008), American Standard Heating & Air Conditioning, A341624P07, Upflow / Horizontal gas furnaces, Downflow / Horizontal gas furnaces, Models CUX1B040A9241A CUX1B060A9361A CUX1B080A9421A CUX1C100A9481A CUX1D100A9601A CUX1D120A9601A CDX1B040A9241A CDX1B060A9361A CDX1B080A9421A CDX1C100A9481A CDX1D120A9601A Pub. No. 41-5016-07
2. Any access door or panel must permit removal of the largest component in the heater at that location
3. Combustion air requirements: see COMBUSTION AIR DEFECTS
5. Garage installations: Boilers installed in a garage must place burners & ignition source no less than 18" above the floor & boiler must be protected from physical damage from vehicles
See details at PROTECTION BOLLARDS for MECHANICAL EQUIPMENT
6. Attic installations: uncommon for heating boilers
8. Crawl space installations: uncommon; in a crawl space on a pad or other noncombustible material which will raise the unit for sufficient protection from moisture.
9. Condensate drain elevation space: a condensing boiler in a crawl space must also be elevated approximately 4-6 inches to allow clearance for the condensate drain to exit the cabinet
10. Condensing boiler venting: American Gas Association has certified the design of condensing boilers for a minimum of 0" clearance from combustible materials with a single wall plastic vent pipe.
See DIRECT VENTS / SIDE WALL VENTS for a complete table of recommended clearance distances from a direct vent gas appliance terminal to other building components or features.
See also CONDENSING BOILERS/FURNACES
11. Masonry flue or shared flue venting: Where the system is routed to the outdoors through an existing masonry chimney containing flue products from another gas appliance, or where required by local codes, then 3" venting of Type 29-4C stainless
steel must be used in place of PVC material.
Appliances having an ignition source shall be elevated such that the source of ignition is not less than 18 inches (457 mm) above the floor in garages.
For the purpose of this section, rooms or spaces that are not part of the living space of a dwelling unit and that communicate with a private garage through openings shall be considered to be part of the garage.
See details at ELEVATE OIL or GAS BURNER 18" ABOVE GARAGE FLOOR - IRC Requirement
Also,
Appliances shall not be installed in a location subject to vehicle damage except where protected by approved barriers.
See details at PROTECTION BOLLARDS for MECHANICAL EQUIPMENT
Original source of the text and illustration above:
...
Below you will find questions and answers previously posted on this page at its page bottom reader comment box.
Can you spot the elephant in this room?
Why hasn't anyone noticed the large cast iron stove, tipped off of its stand and leaning towards a working furnace!
How did it get there, or was the furnace installed with it already there?
I don't think they got a permit for that arrangement. What could an inspector say about this?
Are clearance issues often met up with in your line of work? - Anonymous by private email 2021/06/11
The cast iron stove (black arrow in photo) looks to me like a cook stove in the basement of what may indeed be a pre-1900 building (stone foundation).
Atop the stove bottom we see the back of the cookstove (orange arrow) and in the photo it appears that the stove, with some apparatus piled on top of it, may be leaning towards the boiler - an unsafe condition as I'll discuss in a moment.
As to how that stove got there, in some older homes cooking was done in a basement kitchen, but without a bit of information about the building in this photo: its age, country, city, history, construction, I can't say how this cookstove was used. It looks like a wood-burner but could have been a coal burner. In any event, it's an antique.
It would be no surprise to find an antique cookstove stored in a basement, left there by someone who valued it but had no place to display it.
There are two topics to discuss:
As you'll read above on this page, working space is needed in front of heating equipment - at last 30".
In addition tipping-over heavy objects near enough to the boiler that it could be struck by falling piles of stored items is dangerous. The risks include
Code inspectors and professional building inspectors, home inspectors, service technicians and others find obstructions like those shown in your photo all too often.
One would expect any of them to either move items to perform their work safely or to ask the building owner to move items both to permit working space and to keep the system free from potentially unsafe obstructions and stored materials.
Do accidents ever happen because of stuff stored precariously close to heating equipment? Of course. Your question must be rhetorical.
Working as a home inspector decades ago I often went early to my inspection site in order to become familiar with it before my attention had to be divided between the building and the client.
At a New York inspection I arrived even earlier than usual.
I'd been told that the owners would be at home, and indeed an automobile was in the driveway.
I rang the doorbell to let the owners know I was on-site. Nobody came to the door.
"They may still be asleep," I guessed.
I walked around the exterior of the home in the cold winter air, noticing the usual topics of surface runoff, siding, windows, roof, chimney.... Chimney?
I paused at the home's right side, considering what I could see: it was cold and surely their heater must be running.
But there was no evidence of warm flue gases exiting the chimney.
There in front of me was a low window in the foundation, giving view of the basement. I could see a gas fired heating boiler through the window. And though my hearing was never the sharpest, I thought I heard it running.
I bent over for a closer-look.
"Oh my god" The gas boiler was running full-tilt, but something had fallen against the boiler's flue-vent connector, knocking it apart. The boiler was venting all of its combustion gases right into the basement, and of course those gases would pass upstairs!
All of the gas boiler combustion products were venting into the home, and had been for who-knew how long!
In a panic that the family might be dead or dying from carbon monoxide poisoning, (that would explain why no one answered the doorbell), I ran to the front door, rang the bell repeatedly and pounded loudly on the door while shouting.
I don't remember what I shouted.
I remember being really afraid.
Considering that people in the house were surely dead or dying I had no choice but to enter immediately, however I could.
I kicked in a living room window, leapt through, and ran, heart pounding, to each of the bedrooms ...
No one. There wasn't a soul in the home.
Having turned off the heater and opened windows and doors to air-out the flue gas-filled home, as I was opening the last window my inspection clients pulled into the driveway.
My client, Fred, looked at the smashed window and turned to me with the strangest expression mixing curiosity, wonder, and a little fear.
"I kicked in a window to save the occupants from carbon monoxide," I explained " but no one is at home." I showed my client the disconnected flue vent - which, incidentally, was trivial to repair. The chimney itself was not blocked.
We restored the flue vent connector, turned on the heat, checked the boiler's operation, completed the inspection, and before leaving I wrote a note of apology to the homeowner for kicking in their window. I'd pay for the repair.
I figured the owners would be furious.
They weren't. Instead, the owner called me to express his thanks.
"We were not at home," he agreed, "but we might have been."
...
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