Hydronic Heat between stud wall and adobe wall

OldAdobe

Thinking about adding gas/solar hydronic heat BETWEEN an 18" thick interior adobe wall that has a 4" gap between it and an un-insulated interior 6" stud wall. (Don't ask me what they were thinking!! 2 stem walls!!) Nearly 75' of wall in three sections, forming a rectangular U, in the middle of the house. From experience heating with a wood stove, in the middle/bottom of the U, I know if the adobe stays warm the whole house stays warm. The cavity between the 2 walls is connected at the corners and I can go underneath the door sills so my plan is to run multiple lines of pex manifolded together to heat the bottom of the walls as the gap between the 2 stem walls extends 13" below floor grade. ANY IDEAS/SUGGESTIONS ON HOW TO DRIVE MOST OF THE HEAT INTO THE ADOBE? I am looking at using a Non Perforated Radiant Barrier of Reflective Insulation Foil to hold the pex against the rough adobe wall as much as possible. Any ideas on how many lines of 1/2" pex for a 50 year old, 4000 square foot monstrosity at 7000' elevation in Northern New Mexico? Different load calculators estimate between 150K and 200K btu/hr load, but with the existing solar it is probably closer to 1/2 that.

nicholas bonham-carter

If the Adobe walls get warm from the sun, it might heat the house, but in your case, with a boiler, and interior radiation insulation would keep the heat in the house. Blown in fiberglass might be best here, but pay attention to water vapor.
Can you put the radiant in the floor?—NBC

Zman

Houses with high thermal mass and low insulation do well in climates like yours. The warm sunny days heat the mass. On the cool nights, the mass releases it's energy and keeps the interior warm. The building acts as a giant buffer.

Buildings like yours totally screw up most heat loss calculators. The calculator cannot figure out the stored energy and just sees it as a huge heat loss.

I don't think heating the mass mechanically is a very good idea. Most of the energy will be lost to the outside and chance of a flywheel effect is high.

I do like the idea of radiant walls or ceilings. It would be better to install the panel right behind the drywall so it will give a nice radiant effect to the occupants.

OldAdobe

NBC- Thanks for the comment! They put a roof over the adobe and enclosed it so it never sees the sun! The windows on the south side of the room, it is enclosed in, do add heat to the floor though. It will be a lot easier to add some hydronic heat in the walls, that are completely interior walls now, than tearing up and relaying brick floors!

OldAdobe

ZMan Thanks for the comment! Since they put a roof over the adobe, and enclosed it, all of the heat in the adobe will radiate back into living space.

The solar part of my plan is to circulate solar heated water via heat exchanger during the day since the adobe never sees the sun. I would like as much of that heat as possible to go into the adobe during the day instead of out through the drywall.

Zman

Do you know what your heating design days and cooling design days are? With the solar, you would be wise to heat your domestic water first. You will benefit from that year round.

I would be careful of dumping btu's into a mass that you don't have control of. There will be such a lag in reaction time, you may accidentally overheat yourself, especially in the shoulder seasons.

John Siegenthaler has done tons of articles and books on the subject. I would suggest reading a few as you try to get your head around this.

Posting pictures and or building plans would help everyone understand your project better.