Interesting experience you have had with hydronic heat, Pat. Managing
interior temps with a high thermal mass house can be a challenge.
Although my house is all concrete except for the roof, I chose not to use
hydronic heat. It will be interesting to see how SAM's house will perform
if the interior is not fully insulated from the concrete. There have been
big debates on the best way to insulate a high thermal mass house to deal
with the heat storage issues.
It gets more interesting as you get into the details. The central portion of the ground floor of the house is in-slab hydronics and or forced air heat and cool. This portion of the house is 2x6 stud stick built with lots of glass. The cathedral ceiling goes up to about 26 ft or so with a loft/mezzanine over half of the great room and entry.
The master suite is ICF with a solid 8 inches of concrete in the walls, concrete ceiling, and a slab on grade floor (insulated under the slab) and the hydronic heat is in the ceiling below the insulation decoupled from the ceiling slab. The R-value of the ceiling sheetrock is quite low and its thermal mass is not much either so the response times are fast (thermal time constant is comparatively low.) The floor is mostly carpeted. There is 2 1/2 inches of styrofoam on both sides of the concrete in the walls. With your feet protected by carpet from a cooler floor slab you don't notice the difference in ceiling vs floor heat much.
Set back stats are futile with in-slab heating so you just heat the space constantly and suffer the night time losses/operating costs when the space is not occupied. With my heated ceilings (as in the master bedroom) you can take advantage of setback which is especially handy if, like my wife and I, you may prefer sleeping in a cooler room but like it warmer during the day. We can vary the bedroom temp fairly easily due to lower thermal time constant. The great room in-slab heat has such a long time constant that you can not run lower night temps and higher day temps due to tremendous lag.
An advantage of in-slab heat in the great room with tall cathedral ceiling is that your radiant environment helps keep you comfortably warm as the radiant heat warms objects (you included) much more than the air. Not much heat is lost to convection currents carrying heat to the upper level. Some convection cells do form so some convective currents carry a little heat to the upper levels and when it is really cold out then globs of cold air may fall down on you from the upper reaches of the cathedral ceiling. A Casa Blanca type fan or two running very slowly totally disrupts the convection patterns and you lose the descending cold blobs. If you set the stats so you get some forced air heat too then the air gets homogenized and the convection currents are disrupted. The loft/mezzanine floor over 1/2 of the greatroom-kitchen-entry.wife's office is heated by a high SEER air to air heat pump which does not effect the ground floor much in winter as its heat stays upstairs and can be run on a set back plan. In summer its cool air does materially assist the A/C of the ground floor (geothermal based.)
The walkout basement is so easy to heat and cool it is not worth worrying about setback. The walls are 12 inches of concrete with 2 1/4 inches of rigid foam insulation on the outside. There is 2 1/2 inches of rigid foam under the slab which has 16 inches of septic gravel under it. The basement ceiling is the great room slab floor. The basement ceiling was formed with Panel Deck a horizontal analog to ICF construction so the basement ceiling is massively insulated from the slab overhead. Most of the basement walls are covered with a min of 3 inches of Eastern Red Cedar from the floor to 4 ft up and then with glued on carpet from the 4 ft level to 9 ft ceiling and the rest is sheetrock over cast concrete walls with firing in some spaces.
The basement never gets uncomfortably warm in summer and can be cooled as desired quickly and easily. I did not put hydronics in the basement as it is so easy to maintain a comfortable environment by conventional forced air. I have a decorative gas log parlor stove (LPG fired) with adjustable flame size in the basement and it can easily overheat the space.
Enough!!!! I'll respond to questions and comments but enough already...
For the whole story see the thread on the sister site Country by Net:
CountryByNet.com Forums :: South Central Oklahoma Farmhouse
There have been over 188,000 views of that thread (22 pages long.) I put a lot of info there on the home building in general and considerable stuff about hydronics.
The house is an eclectic mix of construction styles mostly seamlessly integrated into a unified whole. The ground floor is in three major types of construction;ICF, 2x6 stick built, and red iron. The basement is cast concrete and the upstairs is 2x6 stick. Two high SEER air to air heat pumps and a geothermal heat pump with 5 each 200 ft wells. The air to air units have propane backup with outdoor thermostats set to the breakeven point on operating cost of electricity vs propane.
Pat
