Time to heat up mass

How long would it normally take to heat up a mass in an RMH to let the mass still be warm the following morning.  Talking warm as in still keep the room warm...200 sq feet.  Talking, potential zero or subzero F temps outside with some but not the greatest of insulation on the inside of the structure.

Trying to figure if the RMH is worth further investigation or not.  I have a rather unusual situation and trying to figure out how to work around it.  I don't want to have to swelter in the house to get the mass heated up enough to let it still be working for me in the morning.  I don't want to have to heat the house up again in the morning simply because I want the house to be cold when I get home in the evening...cold as in around 45-50 F.  Yeah, a rather different scenario than most people.  The only thing I can figure right now that I could do would be to  only use the heater in the evening but to do that I need it heat up the mass enough in the evening to still keep the mass warm for the morning before I leave home.  While not being big enough to keep enough heat in so it has let the house cool down by the time I get home in evening.  I'm just sure with everything I have heard thus far if an RMH can be designed up to accomplish what I'm trying to accomplish if it would just make me sweat my arse off in the evening and overnight because of the high heat output.

Hi Hank; How warm were you wanting it to be ? Is this your all winter long residence ? If so, then a rmh will work for you, the way you want to run it . If this is a weekend cabin then not so good . If you don't want a lot of radiant heat but stored heat then build with heavy firebrick for your core , cover 80% of your barrel with cob, Use large stones in your mass, surround your mass with rock or brick. You will want as much heat sink as possible. This will allow your rmh  to store heat rather than radiate heat from the barrel. At the start of the season you would need to warm up your mass, (easy to do if your there every day)  Once your mass is warmed up a 2 hr fire should replenish your heat.  A one hr or less fire in the morning on the coldest days might feel good to you as well.   We really need more info to give you a better answer.

Yes, permanent residence.  I gave up driving 6.5 years ago so I get around by bicycle and have found what works for me to keep me dry while on the bike while riding during the winter months.  I get home bone dry and prefer to stay that way.  I know if I walk into a 70-75 degree house I'll immediately, before I can even get the clothes changed, be sweating my arse off...warm house combined with 98.6 degree body equals immediate sweat.  Hence why the past numerous years it has always been nice to walk into a cold house, 45-50 degrees.  I turn on the electric heat, used to be propane until the heater stopped working and the company has been out of business for around a decade and you can no longer get parts.  After turning on the heat I could change clothes and the body temp would drop so that by the time the house would start to get back up to around 55-60 degrees my body temp had dropped and I wouldn't break a sweat.  Perfect match.

Normally I have always kept the house around 60-62 degrees , I could go up to 65 and not complain any.  Prefer not much warmer that though.  I would rather put clothes on to stay warm than to be taking clothes off to cool down.  Again, keeping the body used to the cooler temps helps to keep the conditioned so I don't sweat while I'm out riding during the winter months.

Another problem I see with what you suggest is a post and pier 'foundation'.  I'm not on a full wrap around, concrete block foundation, just on a post and pier(concrete block) style foundation so weight does become a bit of an issue when you really start adding a lot of insulation for the mass and the heater as well.

Also, around here I never hear of mud slides.  This is called the Granite State for a reason.  Pretty much trying to even put a shovel in the ground is quite difficult thanks to all the the darn stones you keep hitting with every shovel load.  You can get hard rain and a lot of it, like Hurricane Irene five years ago and you don't run into problems of mud slides anywhere.  Where does the clay for the cob come from in a situation like this.

A fellow granite stater! There's a few of us here.

My RMH has most of its mass made with concrete. It works very well. I do have cob around the burn area, and most of the clay we dug out of the ground. Most of the sand too. It can be found, but you do need to look around your property a bit.

But you have identified what I believe is the biggest hurdle preventing RMH systems from becoming more common: the actual science of heat control. As was mentioned you can simply cover up more of the barrel around the heat riser to make it more mass heating than radiant (immediate) heating. But there isn't yet a formula for calculating how much to cover it - you have to experiment. How much to use would vary depending on the properties of the mass material as well as what is being burned.

It is also still an art and not a science to decide when to stop a burn. In my system I usually stop when the temp in the cabin gets to about 85, which is above my comfort level. But by morning the place is still nicely warm.

Of course when it gets really cold outside I do need a morning fire as well, but mostly just to keep the mass primed.

Hi Hank; Yes your floor does need to be able to hold the weight.  If your mass is situated across multiple floor joists that helps tremendously, two  extra pier blocks and a beam should take up any extra weight, (its really not more than a waterbed).   Other thing is raising it a few inches off your hardwood floors with bricks so heat can pass underneath, and spacing it out from a wall for the same reason. I lived in Vermont long ago and there was clay there so NH has some as well . Ask a local dirt contractor or the local road crew (the guy on the loader not the boss in town) or... buy 50# sacks of dry powdered fire clay, they cost apx. $10.00 each here.  Sand is available at rivers or home depot.  as Ron said you can use concrete in your mass, just be sure to put large chunks of granite in with it (rock holds heat more than concrete)  Sounds like Ron likes it warmer than you do , 85 would be outside your comfort zone...  Every rmh is different, and every space your trying to heat is unique.  The idea behind a rmh is to save wood (money) you can still use your electric space heater if you want too, but once you experience the whole room warmth that a rmh produces you will not want to.  The other really nice thing about a rmh is NO ELECTRICITY REQUIRED ... the power has a tendency to go out during those below zero  
storms... your rmh will happily sit there radiating warmth all night long. It also will burn any dry wood product (pallets , broken branches , construction waste , pine cones !) No need to own a chain saw if you don't want to.  They are not for everybody (though they should be)  No smoke , no creosote , no ash to speak of , if I was making laws it would be required to have a rmh ... they are good for the environment !