Catalytic Fireplace vs Rocket Mass Heater/Stove

We will be building a passive solar home in Maine this fall and are looking into a secondary source of heat. We are considering a catalytic fireplace and have recently been introduced (thanks to this website) to rocket mass heating. We are trying to understand the different between the two and if anyone can provide their experience with either/both?

Secondarily to heat, would either help prevent pipes from freezing? I only bring this up because we are having one heck of a time finding home insurance for this project and one of the reasons insurance companies have sited for declining coverage is the high probability of pipes freezing and inadequate secondary heat source.

Thanks!

Ann

Catalytic is a lot lighter weight.
AND, most people can run a stove. Open every 4 to 6 hours, load, repeat.
AND clean the chimney every month you use it.


Rocket Mass Heater weighs 3 to 8 tons depending on size.
Your house has to be designed around the heat source if rocket, cuz you gotta mess with it every 30-45 minutes.
It is way more efficient, like less than half the wood for same heat performance.

For occasional or just backup the catalytic is easier for everyone, inspector, insurance, friends.
Almost no new learning for any of them.

If you stay in your house, inside the house, rockets are great long term heaters.

Are you on the grid?

Insurance companies like secondary heat that's on a thermostat and kicks in even if nobody is home. Electric heat is an expensive option. Pellet stoves can be set up in a standby mode with a thermostat.

Thank you Pete, I was not aware of the weight.  I had not researched that far yet.  

Douglas, we will be completely offgrid as it will be too expensive to bring electricity to our site. We will get our electricity through solar panels/batteries.

When you say a catalytic fireplace are you referring to an actual built in fireplace or a freestanding stove.   Fireplaces work but your options are very limited.   Stoves you have many more options.   I load mine in cycles depending upon outside temps.  Either 8 12 or 24 hours.  Many can do the 8 and 12 hour cycles fewer can get to 24 but there are some that can.  If using it properly once a year is most common.  Some people easily go 2 years with no problems

I believe when Ben mentions 1-2 years, he's referring to chimney cleaning, which is what I've seen from those using a standard wood stove, they get in there before winter and clean out the buildup.

Ben when you mention loading at most every 8 hours, is that with the damper closed a bit and the wood can then smoulder, or are you using a pellet-fed system with a hopper? If it's by closing the damper a bit to smoulder, I believe that is where part of the efficiency of a RMH can shine. A RMH has no damper, instead you want to burn the wood as hot and fast as you possibly can, to get to a far higher temp than a metal stove could tolerate. That ensures total combustion and no smoke or unburned byproducts, and then the high thermal mass that the exhaust runs through absorbs that heat so your exit temps are around 100-150F instead of the much higher temps a normal stove produces. Then that large mass can radiate the heat into the space for hours, and you only have to load a couple pounds of wood once or twice per day.

I am currently using a catalytic stove.  Which is what the original poster asked about.  In a catalytic stove the damper is used to bypass the catalytic combustor untill the stove reaches operating temps.  One it has you close the damper and all of the exhaust is directed through the cat where the remaining combustibles are burnt out of the exhaust.

Once you do that you control the heat output and burn time by controlling the incoming air.  Doing this allows the wood to smoulder but still burn very cleanly.  That is how I am able to burn for up to 24 hours one load of wood in my 2.5 cubic foot stove.  

The amount of wood needed to heat the house depends upon the BTU load of the house being heated.  Dry wood contains roughly 8000 to 10000 BTUs per pound.  So based upon the 75% to 80% efficiency of most modern stoves you can figure out how much wood you need based upon heat load calculations.   My house simply could not be heated with the BTUs contained in a few pounds of wood burnt a couple times a day.

The best application I saw when calling house to house in north east Maine was an octagon log house with a large mass stone fireplace in the center. The stone when heated would radiate heat to all parts of the house long after the fire was out.
A catalytic fire place may burn wood efficiently but an hour after it is out there is no more heat being supplied to the living space.
To meet building and insurance requirements foundations and waterlines have to be six feet deep.  Your plans have to show that the water line enters the hose away from exterior walls an  dose not travel through or along exterior walls.  The mass of your RMH could be specified as a protective heat sink for the pipes.

It is true that rocket mass heaters need to be tended every half hour to hour or so depending on the style while they are burning... but after a couple-few hours depending on conditions the fire ends, the heater is sealed up, and you coast on that heat for 12-24 hours with no fire and no cold air being sucked through the house. The warm surfaces make everything comfortable even if the house air temperature is lower than "normal".