RMH Portland Building Code

Everywhere I go, I see mentions that you can have a RMH in Portland.  Erica Wisner has posted this link in several places saying "...the Rocket Mass Heater code-style guidelines for Portland, Oregon:"  Www.portlandonline.com/BDS/ATAC.  From their website also comes this link:  Draft 2 of Rocket Mass Heater code: (historic interest - see current version July 2012) which is still again the same page which does not contain the current version of the code, it's a cover page.  I cannot for the life of me find the actual code! Or the guidelines!

I've done searches with many variations on wording, looked through code listings, searched for hours on the internet.

Please please please, can somebody just post a bleepity bleeping link?

I wanna scratch my eyeballs out!

Thank you for your time.

Hi Solomon;    Is this something you have looked at before?

No, I have not seen it before.  But I figured if I'm going to build a secret RMH in Oregon, it might as well be according to code.  Maybe I'll get lucky and Jackson County will adopt it some day.

I found that document, but that's not the code.
This is the closest I've seen so far, from Erica's site:

Draft 2 of Rocket Mass Heater code: (historic interest - see current version July 2012)

1. Scope:

1.1 This guide covers the design and construction of Rocket Mass Heaters, a subset of solid fuel burning masonry heaters. It provides dimensions for site constructed rocket mass heaters and clearances that have been derived by experience and found to be consistent with safe installation of those rocket mass heaters.



1.2 Values given are in English measurements, and are regarded to be standard. All dimensions are nominal unless specifically stated otherwise. All clearances listed in this guide are actual dimensions.



2. Definitions:

2.1 Combustion unit: The area where fuel is consumed and clean exhaust produced; comprising the fuel feed, burn tunnel, heat riser, barrel, and the manifold.

2.2 Combustion unit base: Area composed of the fuel feed, burn tunnel, insulation and casing.

2.3 Fuel/air feed: Area where fire is lit and fuel is added. This is the sole air intake.

2.4 Burn tunnel: Horizontal area where initial combustion occurs.

2.5 Heat riser: Internal chimney, insulated for high-temperature combustion and draft.

2.6 Barrel: Metal or masonry envelope around the heat riser that radiates heat.

2.7 Manifold: The connection between the combustion unit and the heat-exchange ducting.

2.8 Heat-exchanger: The area that absorbs heat from the heat exchange ducting and re-radiates it over an extended period of time. Comprised of the heat exchange ducting, thermal core and casing.

2.9 Heat exchange ducting: The flues that carry hot exhaust gas through the thermal mass.

2.10 Thermal core: Area directly around heat exchange ducting.

       2.11 Thermal earthen masonry:

2.13 11 Casing: Durable external layers to protect thermal core, provide additional thermal mass, maintain desired surface temperature, and allow decorative expression.

2.12 Flue exhaust: The portion of the ducting after it leaves the thermal core.

2.14 13 Cleanout: Capped opening for maintenance access.



3. Significance and use:

3.1 This guide can be used by code officials, architects and other interested parties to evaluate the design and construction of rocket mass heaters. It is not restricted to a specific method of construction, nor does it provide the principles to be followed for the safe construction of rocket mass heaters.

3.2 This guide is not intended as a complete set of directions for construction of rocket mass heaters.

3.3 Construction of rocket mass heaters is complex, and in order to ensure their safety and performance, construction shall be done by or under the supervision of a skilled and experienced rocket mass heater builder.



4. Requirements:

4.1 Sizing:

4.1.1 6" flue rocket mass heaters can be installed for any heated space 1000 sq. ft. or less.

4.1.2 8" flue rocket mass heaters are typical and appropriate for any installation.

4.1.3 Cross sectional area shall remain consistent throughout the system except in the barrel and manifold, where it may be larger.

4.1.4 Ducting may be tapered to reduce diameter by 1" in the final third of its length to improve gas flow.

4.1.5 Total ducting length from manifold to exhaust outlet may be up to 60 feet, with 30 to 50 feet being typical. NOTE: Some configurations within this range may require special design consideration to ensure proper exhaust.

4.2 Dampers: Shall have no dampers installed that can obstruct free flow of exhaust gas. Exception: A two-way flap or valve which maintains >100% flow may be used between alternate exhaust paths.

4.3 Foundation: The combustion unit base, heat exchanger (no more than 36" in height from foundation), and bench back (no greater than 48" in height from foundation) shall be supported by a 4" concrete slab or equivalent. All other configurations shall have an engineered footing.

4.4 Combustion unit: Shall be constructed in either earthen masonry or refractory materials. If refractory materials are used, an expansion joint shall be included between combustion unit and earthen masonry.

4.4.1 Mortars, when used, shall be clay-sand, fire clay or suitable refractory mortar. Mortars may be omitted if using monolithic earthen masonry as an external seal.

4.4.2 Fuel feed:

4.4.2.1 Shall be constructed of fire brick, clay brick or equivalent refractory material rated for over 2200˚ F.

4.4.2.2 Shall have an emergency shut down lid.

4.4.2.3 Shall be the sole air intake.

4.4.3 Burn tunnel:

4.4.3.1 Shall be constructed of fire brick, clay brick or equivalent refractory material rated for over 2200˚ F.

4.4.3.2 Shall be insulated with 2" of clay-perlite insulation or equivalent underneath, above, and on all sides except the fuel feed and heat riser openings.

4.4.4 Heat riser:

4.4.4.1 Shall have a minimum height of twice the burn tunnel length.

4.4.4.2 Shall be at least three times the height of the fuel feed.

4.4.4.3 Shall be constructed of firebrick, clay brick, metal flue or equivalent refractory material rated for over 2200˚ F.

4.4.4.4 If constructed of metal flue, it shall be free from holes, wrinkles, burrs, jagged edges or other obstructions. Metal shall be high-temperature stovepipe or steel.

4.4.4.5 Shall be insulated with minimum of 2" of clay-perlite insulation or equivalent.

4.4.5 Barrel:

4.4.5.1 Shall be free from holes, wrinkles, burrs, jagged edges or other defects.

4.4.5.2 Any existing paint or surface coatings shall be removed. High-temperature coatings rated for woodstove application such as stove enamel, cast-iron seasoning oils may be used.

4.4.5.3 A cleanout shall be located near the base of the barrel that allows access to the manifold and initial ducting, or the barrel shall be configured for removal.

4.5 Heat exchanger:

4.5.1 The heat exchanger rests on 4 inches of dry stack masonry, above or including the foundation.

4.5.2 Ducting:

4.5.2.1 Shall be metal flue, ceramic flue liner, or well pointed brick.  Metal flue shall be free from holes, wrinkles, burrs, jagged edges or other defects.

4.5.2.2 Shall be embedded in a continuous layer of earthen mortar for both thermal contact and gas seal.

4.5.2.3 The length of ducting encased within the heat exchanger is typically 15 to 40 feet.

4.5.3 Cleanouts:

4.5.3.1 Shall have a sufficient number of cleanouts such that all sections of the ducting shall be accessible.

4.5.3.2 Cleanouts shall be the same minimum size as system: e.g. 6" diameter for a 6" flue rocket mass heater and 8" for an 8" flue rocket mass heater.

4.5.4 Thermal core shall be encased with a minimum of 2" thermal earthen masonry around the ducting. a minimum 2" of heat-tolerant masonry in thermal contact with ducting. Earthen masonry for thermal core shall be dense and without organic fibers or air pockets.

4.5.5  Casing:

4.5.5.1 Total thickness from ducting to surface from ducting, for a 6" system shall be at least 4" depth around the first 10 feet of ducting, and 3 inches around the remainder.  

4.5.5.2 Total thickness from ducting to surface to surface from ducting, for a 8" system shall be at least 6" depth around the first 10 feet of ducting, and 4 inches around the remainder.

4.5.5.3 Casing shall be compatible with thermal core, such as earthen masonry finishes over an earthen masonry core. Portland cement casings are not compatible with an earthen masonry core.

4.6 Flue exhaust:

4.6.1   Flue exhaust may be a manufactured chimney, lined masonry chimney, or horizontal exhaust.

4.6.1.1 Manufactured chimney exhausts shall be installed according to manufacturer's instructions and local building codes.  

4.6.1.2 Lined masonry chimneys or horizontal exhausts shall be suitable for low-temperature flue-gas exhaust from combustion appliances, such as a furnace or gas-powered dryer. Exhaust temperatures can be designed to reach from 70F to over 350F within the scope of this code, so temperature-appropriate exhaust treatment is at discretion of builder.

4.6.1.3  Horizontal exhaust shall be constructed similar to a dryer vent or other low-temperature flue gas exhaust.

4.6.2 Exterior sections of exhaust shall be located away from building air intakes and occupied areas, and protected from wind, rain, and vermin.

4.7 Clearances:

4.7.1 Fuel feed: A minimum clearance of 18" shall be maintained from combustible materials to fuel feed.

4.7.2 Combustion base: A minimum clearance of 4" shall be maintained from combustible materials to all surfaces.

4.7.3 Barrel: A minimum clearance of 36" shall be maintained from combustible materials to all surfaces, if installed without a heat shield.  A minimum clearance of 18" shall be maintained from combustible materials to all surfaces,  if installed with a heat shield including 1" air gap.

4.7.4 Heat exchanger:

4.7.4.1 Minimum distance between ducting and combustible wall shall be 6".

4.7.4.2 Heat tolerant fabric shall be used for all seating surfaces. Any fabric used for seating surfaces shall be heat tolerant.



5 Inspections

5.1 Inspection Points for Rocket Mass Heater Installation:

The main inspection should be performed after combustion unit, ducting, and exhaust have been installed, and while ducting is still exposed.

5.1.1 Confirm measurements:

Ratio of heat riser to burn tunnel and heat riser:

___Heat riser is about twice the length of the burn tunnel, or taller

___Heat riser is about three times the height of the feed tube, or taller

Cross sectional areas:

___Consistent cross sectional area throughout system except barrel, manifold, and possible 1" decrease in final third of flue.



5.1.2 Confirm clearances:

___EITHER ___36" from all barrel surfaces to combustibles.
OR: ___18" from all barrel surfaces to heat shields with a 1" air gap.

___4" from combustion base to all combustibles

___Room for sufficient masonry thickness around ducting.



5.1.3 Confirm maintenance elements:

___Cleanouts provide access to manifold, ducting, and exhaust.

___Exhaust outlet is properly installed, AND
___ protected from elements and vermin.

___Maintenance and operation manual is in good order, with accurate as-built drawing(s).



5.1.4 Confirm structural elements:

___Foundation appears sufficient to support final installation (4” slab or engineered footing).

___Suitable earthen and/or refractory materials are being used.



5.1.5 Inspector may request that Rocket Mass Heater be fired. If so:

___Confirm proper drafting.





5.2 Inspection Points for Completed Rocket Mass Heater

For a previously completed or engineered installation, the following may be used:



5.2.1

___Confirm measurements, clearances, maintenance and structural elements, as above.



5.2.2 Confirm masonry integrity:

___Masonry thickness around ducting conforms to minimum standards (3-6” or more).

___No cracks apparent in casing or visible masonry.

___Casing materials are compatible with thermal core. (No cement stucco over earthen masonry).



5.2.3 Request that Rocket Mass Heater be fired. If possible, have applicants fire their heater the day before inspection, and then again in the presence of the inspector, to simulate normal operations.

5.2.4 Confirm performance:

___Draft and seals function properly; no indoor smoke observed.

___Exterior exhaust appears clean (white or transparent)

___Surface temperatures are within tolerances (Safe to touch, except barrel and fuel feed).



5.2.5 Check any special features:

Installations may include __Heat shield(s), __Exhaust chimney, ___Bypass valve, __Gaskets/expansion joints, __Structural reinforcements, or ___Other features.

Confirm that features

___Conform to as-built drawings.

___Appear to be properly installed and functional.



Inspection Points:



An inspection should be performed after ducting has been installed and while it is still exposed



Confirm measurements:

1. Proper ratio of heat riser to burn tunnel and heat riser.

2. heat riser is twice the length of the burn tunnel

3. heat riser is three times the height of the feed tube

4. Confirm proper cross sectional areas.

5. Consistent cross sectional area throughout system except barrel,

manifold, and possible 1" decrease in final third of flue

6. Confirm clearances

7. 36" from all barrel surfaces to combustibles.

8. 18" from all barrel surfaces to heat shields with a 1" air gap.

9. 4" from combustion base to all combustibles

10. Room for sufficient masonry thickness around ducting.

11. Confirm suitable footing and foundation.

12. Confirm appropriate cleanouts.

13. Confirm exhaust flue is protected from elements and vermin.

14. Confirm existence and orderliness of maintenance and operation

manual.



Inspector may request that Rocket mass heater be fired.

If so: Confirm proper drafting.

Chris (Uncle Mud) McClellan and I talking about code and insurance for rocket mass heaters: