Let us not ignore the floor. Although traditionally the priority for insulation has been first the roof/ceiling then the walls and then the floor, maybe if it gets considered. It is important to insulate under a slab and to have a thermal break between the dirt outside the foundation and the floor, especially in cold climates.
My basement has 4x8 sheets of 2 inch rigid high R-val foam under the slab and on top of the 16 inches of washed septic gravel. The basement floor has no hydronics and so far this winter the basement T'stat's thermometer has run at about 72 degrees all the time with its thermostat shut off. I have central hot and cold air for the basement but it doesn't run much, especially when it is turned off. The walls have R-11 rigid foam insulation on the outside between wall and back fill.
There is some heat coming from "Hydronics Central" where all the manifolds and controls and hot water storage is located in the basement. I have put foam insulating sleeves over all exposed hydronic lines where I could and that reduced the heat getting out of the system into the basement a BUNCH.
I have a friend who had a recreational leashold about a hundred yds from mine in Baja California. He had a hydronic heated earth sheltered concrete home (about 5000 sqft) rented out while waiting to find a buyer. This was in Idaho. He got a call from his renters claiming the hoiuse and DHW heating systems failed.
This was in the depths of winter with several feet of snow on the ground in Idaho. He had to drive all the way back to check it out. Seems that they could still take showers but the water wasn't quite hot enough and the house was down to a uniform 68 degrees not the 74-75 they preferred. The solar preheat on the DHW was maintaining a fair temp, just not the 125 that the gas DHW heater topped it off to when the system was working correctly.
Anyone guess what the MALFUNCTION was??? Yeah, the idiots let the propane tank run dry and the house was still holding 68 after a week. There was no problem except for the short between the renter's headsets. One propane delivery later and all was OK so my friend could drive back to his winter haven in Mexico.
Over the Christmas holiday my master suite lost about 4 degrees in 3 1/2 days. I turned the 'stats down as an experiment to see how the various portioins of the house faired.
NOTE: You can use programable thermostats in a hydronic installation if you use them wisely, in situations where they can help. One such application is the bedroom where some folks prefer cooler sleeping temps than daytime temps. With ICF construction you are decoupled from much of the thermal mass (the walls) by (in my case, a minimum of 2 1/2 inches of styrofoam) and the hydronic heat is in the ceiling with only a layer of sheetrock for thermal mass. Sheetrock has a rather low R-value and not much heat storage for a single layer. The response time of a hydronic system in these conditioins is pretty good, way faster than a hydronic slab. So if desired you can run lower night temps and get up to the desired daytime temps pretty fast. Most of the floor has pad and carpet so there is a decent R-value between the slab and the room's volume. (There is some tile but it isn't so cold underfoot as you might think since it is heated by IR from the ceiling and the slab it is on is insulated from the dirt.
Additiionally, my geo heatpump can provide hot air along with the hot water if desired. If you really wanted to get the morning temp up to the daytime setting in a hurry you could program the separate hot/cold air controlling t'stat to give hot air to help out.
This can be used to advantage during the "shoulder months" where in our climate we have a couple hot days and then a cold day or two and then hot and then warm etc. We have random, rapid, and large temp fluctuations. If the house is comforable and the slab is heated as required to shed the same heat as the room looses to the outside then all is well until the next day is 25 degrees warmer and then you can easily overheat as the slab can't respond fast enough.
So, during the shoulder months, I can set the "air" thermostats to assist the "water" thermostats. I can derive part of the heating from the floor. The floor stays warm and comfortable but not hot enough to supply all the required Btu's. The floor heat is supplemented with hot air when required. Then on a hot day the air stat shuts off and you don't overheat (as much if at all.)
The two stats can be set for mid winter cooperation as well. If the air stat is set a couple degrees below the water stat then no hot air is typically delivered but if during a party a lot of comings and goings and wandering out to see the view from the back porch brings in a lot of cold air, then the hot air kicks on and brings the air temp back up to within a degree or two of what it was prior to opening the doors. Once the air stat is happy it shuts that system down and you are hydronic only again. The hot air gives you the ability to respond much quicker to a change of demand. Without the hot air, after thte doors were closed the air would warm back up in a while and all would be OK but you wouldn't be comfortable for a while.
If you want or need a faster reaction time for your radiant heat then consider radiant ceilings. They work just fine and respond to changing demands much quicker. They work very well with ICF walls since the room air is isolated/insulated from the thermal mass. Radiant ceilings do warm the floors, even slab floors, just not as much as in-slab hydronics. In carpeted spaces, radiant ceilings warm the floors quite well as the R-value of the floor covering prevents the heat from escaping and the rug gets warmer (my feet are happy.) In fact if you want thick pads and carpets then radiant ceilings are a better choice.
At a given delta T between the inside and outdoors (temporarily ignoring infiltration) there is a steady state heat loss, a given number of Btu's lost per hour. If your heating system replaces those Btu's then the inside temp is constant. This is true no matter what the wall's thermal mass is. High thermal mass tends to dampen variations in temperature but thermal mass alone will not reduce your requirement for Btu's to replace those lost to the outside. That is the job of insulation and to an extent reduction of infiltration.
As far as a thermometer is concerned it really doesn't matter where the Btu's come from, the floor, the walls, the ceiling, or a 55 gal drum converted to a stove for burning junk mail. It is like the lady of the evening and the customer. She doesn't care HOW you got the money just THAT you got the money. The only "MAGIC" regarding in-slab hydronics is that you are directly heating a large thermal mass and it acts like a giant flywheel to help even out variations in temp. It is a good news bad news story. The good news is that it won't change temp very fast and so is comfortable and contributes to stability (usually.) The bad news is that it doesn't change temp very fast and when it is shedding enough Btu's to make you comfortable at a specific delta T it can overheat you if the outdoor temp spikes or you will be chilly if the outdoor temp plumets.
In-slab hydronics with no additional bells or whistles works best when outdoor temps are slow changing. In-wall hydronics invites punctured water lines and should not be used in or below picture and shelf hanging heights. In ceiling hydronics is good and it is easy to retrofit, way easier than retrofiting in-slab into (onto?) a slab floor.
I have in-slab and in-ceiling hydronics in my shower. If you raise the radiant environment suficiently then you don't need a door or curtain for the shower for comfort reasons.
There is also hydronic cooling and dehumidification. It is typically a BAD idea to try to cool your slab enough to cool the house as the RH will go up and you will get wet tile floors and/or soggy carpets. hydronically cooled upper walls and ceilings have been done successfully. There are some hydronic cooling and dehumidifying systems that work well but look a little too INDUSTRIAL for my taste.
There are hydronic heaters made to install under base cabinets and to pull in and then emit their heated air in the toe kick space. I recycled that design for a distributed hydronic heating and cooling/dehumidification system. The bid from the manufacturer for the required mods was quite modest but could be done as a DIY project just fine. There was just one minor problem, preventative maint sort of thing where you use compressed air or a water hose to blow lint and dust out of the unit. All NON-TRADITIONAL activities focus resistance to a new concept.
If you like metal sculptures and reflecting pools then I have the design for you! Yuu run refrigerant from a compressor in a metal sculpture, say a tree with leaves) which then quickly frosts over in a beautiful display of Jack Frost right there in your house. After the thickness of the frost and ice gets to be too insulating for high efficiency of cooling and dehumidification is retarded the unit goes into defrost mode and the ice melts and chunks fall into the reflecting pool hitting leaves and making delightful tinkling sounds and melting in the pool which overflows to wherever you want the water, separately plumbed for irrigation, toilet flushing, or down the drain.
Maybe better you would like a waterfall wall. A wall can be covered in thin decorative metal in the form of several narrow steps (ripples.) The freon in tubes on the backside of the metal causes the metal to frost up removing humidity from your indoor air. The defrost cycle causes a cascade of ice and water to run down the ripples of the structure into the pool below were excess is plumbed away. Since comfort is largely a result of your radiant environment a large cold surface will cause occupants to feel cool as the radiant temp of the wall is so low it basically SUCKS heat out of its surroundings, including you.
Pat
