A client recently requested a dual-fuel heater that would be able to burn pellets. He is building a new home on Lake Memphremagog in Quebec that will eventually become a retirement home.

The house is super-insulated and off grid, and the client wishes to have the option of being able to continue to operate the lower masonry heater (of a stacked pair) as long as possible into his future old age, and not be reliant on fossil fuels once he no longer can manage firewood.

He is a scientist, has done extensive research, and came with a design proposal. He agrees that this is an experimental heater, and is willing to assume any risks involved.

Preliminary

I drove down to the HPBA show in Atlanta in March 2008, and had a close look at the various pellet stoves in the outdoor burn area. Lopez Labs partner Jerry Frisch also attended the show, and I discussed the project with him. In 1992, I had seen a pellet conversion on a heater in Jerry's basement in Everett, WA. It was a retrofit kit designed for wood furnaces, known as a "Collins Hopper 4000". Jerry said he was no longer using the hardware, and generously offered to ship it to me.

Online

Pellet Basket retrofit for a fireplace

This is a simple retrofit that allows you to burn a load of pellets in batch mode. It would be an obvious option to evaluate for a masonry heater, since it is simple.

Shown above is a schematic of how a typical continuous-burn pellet stove works.
A small auger moves the pellets from a supply hopper to a "burn pot".
Forced air is blown onto the pellets to combust them.
In addition, there is often an ignition mechanism (not shown).

The Collins Hopper:

Pellets can be burned either in batch mode in a basket, or continuously in a burn pot. The Collins Hopper
was an example of a continous burn system:

This is a photo of the Collins burn ring. Forced air comes through the 1"x4" steel tube at the left, into the 1"x1" square tubing ring, through a series of 1/8" holes. A lip is welded to the top to retain the pellets in the ring.
Pellets, metered by an auger, drop by gravity through a separate 2"x4" tube, and hit the guide chute shown near the bottom of the 1"x4" air tube.

Other Research

Alex Chernov sent in this image from the Austrian stove show that he attended last year.
It is the firebox of a pellet burning Kachelofen.

The stove fires in batch mode. A hopper is loaded through a gasketed fueling door, and the
pellets drop down behind the large ceramic baffle into the burn pot/basket. The burn pot
operates with natural draft. The ceramic baffle is air cooled, to prevent the fire from going
up into the pellet charge. (see illustration, below).

Brochure from LEDA in Germany.
Compare with Alex's photo

Patents

A patent search turned up a few that were interesting.
More details

Miscellaneous Research

Page of interesting images of pellet burn pots, etc.

Implementation:

An angled opening in the rear wall allows for installation of a Collins type burn pot with pressurized air supply tube and pellet feed tube.
Visible at the back of the floor is one of the two air inlets that are standard on the current Heat-Kit
(see http://heatkit.com/html/lopezm.htm )
This is normally occupied by a secondary air grate.
Everything is raised off the floor 8", to allow for a batch burn basket scheme as well.
The preferred scheme is a large basket with an enhanced burn rate (in batch mode) to be fed from a hopper behind the stove.

Rear view.

Collins burn pot.
If a batch basket of the same size were used instead, the loose firebricks could be arranged as shown to form an air supply plenum around the basket.
If the plenum columns are capped at the top, chimney draft will force the air through the basket.

The client's plan at this stage is to construct an experimental basket from wire mesh, and try out the above configuration.
The basket will be larger than shown, eliminating the loose firebricks on the sides, and using the firebox walls to create the air plenum.

Future results will be reported on this page.

If you have any interesting material to add, please email me at mheat(at)heatkit.com