Advice on hydronic radiant heat partial install

KennethO

Hello.

A little background. This house was built and installed with in slab radiant heat in the basement. It's 14 pairs(28 pex pipes total) for the basement and 2 pairs(4 total) for the master bath. The house is heated by a split unit geothermal system. Main does the basement/main floors and the second unit does the 2nd floor and hot water. The original owner never finished the radiant system or gave us his plans and im working on trying to complete it. He was an electrical contractor and has all the t-stat, power and even a galvanized panel installed and ready to go for the manifolds. Total house sqft is ~7500 with the basement about 2500 sqft.

I've been doing tons of research and I'm very capable. But I'm wondering what's going to be the best option for doing the heating. The house is all electric but has also been plumbed for LP if needed. Since radiant is a winter thing I would assume something like a LP mini boiler would be more efficient than an instant or watertank style heater. This is what I'm stuck on. The manifolds are strait forward and I believe the flow center depends on the heating choice. Local installers wanted something like $. I've done my own hvac and know that is just an insane amount.

Has 8/3 12/2 and t-stat wires already ran.

Pics included.

Thanks, Kenny.

hot_rod

This calculator helps you determine various fuel cost optiuons.

87% is a realistic number for LP, a mod con high efficiency boiler could reach 90%

Electric boiler at 100%

Be sure to use actual delivered Kwh cost, with any or all the fees added in. The bottom line divided by the amount used. Same with LP.

https://coalpail.com/fuel-comparison-calculator-home-heating

DCContrarian

Any chance of tapping into the geothermal?

hot_rod

so radiant in the basement, 2500 sq. Ft.?

Total house is 7500, what heats the other 5000 sq ft. Forced air geo?

KennethO

The whole house is conventional forced air geothermal including the basement. The basement floor and master bath has radiant as an extra for those cold days. I suspect that's why the previous owner/builder wasn't in a big hurry to finish it since technically it wasn't necessary. But it would be dam nice on these sub zero nights since we do spend a lot of time down there.

KennethO

Possibly, im currently looking into that. The main unit has extra water load out ports for hot water etc. But they haven't ever been hooked up and the unit is probably ~14-16 years old(atleast 12 from us). So I'd have to run some tests on the internal grunfos circulation pumps on that circuit. Not sure yet if its free and the valves work. But I plan to test this week if I get time.

My plan was to get a basic idea of the options w/o it going threw the geo just incase and adjust accordingly if I do manage. Either way I'm not sure if it could handle the heating load by itself and that's probably why he had ran a 220v line to the location for an electric heater to assist it.

hot_rod

2500 of basement and a master bath shouldn’t take much in the way of a boiler. Basements under heated space in the ground would be a low load. A load calculation would pin down an exact number. How warm does the basement stay now?

I’d guess all the radiant would require 20,000 btu/ hr or less maybe a 6 kw electric boiler, a LP tank type water heater. Or a 50K mod con boiler are some options.

If the basement stays 55 or more now, the load will be even less.

mattmia2

usually you do it the other way around, the radiant provides the base heating and the warm air adds additional heat if you can't get enough radiant tubing in the space to cover the loss of the structure and to make up for things like doors opening and such.

if you don't have the heat loss that was used to design it, the first step will be to calculate heat loss of the building and each individual area. you can then compare that to the capacity of the geothermal to see if it can pick up the additional loads. there are also some ways to use that heat loss and the history of the weather over past heating seasons along with your bill to figure out the approximate efficiency of the geothermal. that will tell you if the geothermal or lpg is less expensive to operate for the new areas. i suspect that adding to the geothermal will be the way to go if it has the capacity.(although having a second heat source, especially one that can run off a small generator certainly has advantages)

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1842891#Comment_1842891

Continuing this thought, there's a real risk that warming the floor to a temperature that is noticeable will overheat the basement.

The formula for heat output from a floor is two times the temperature difference between the floor and the air. There's no getting around that. A house built this century I would expect the basement to have a heating load of less than 10 BTU/sf, which would correspond to the floor being 5F above room temperature. That won't be cold to the touch but it won't be noticeably warm either.

KennethO

https://forum.heatinghelp.com/discussion/comment/1842893#Comment_1842893

That's what I'm trying to achieve. Floor heating in the winter with central air as needed. While it's "fine" now and fully functional, it can be better and more comfortable in the process. To get it functioning as it was probably originally planned for. I just believe since radiant was primarily a heating option the previous owner wanted to get the AC/Heat done to get get moved in and finish it up later.

This home was purchased during the 08 fiasco and built in 04/06 I believe. So I'm sure it was just put on the back burner. So definitely very modern.

I would have thought it would require a lot more energy to keep temp. Thats pretty interesting.

hot_rod

the radiant floors in a low load basement will warm the space to the ambient air temperature you desire without an issue. The floor may not be warm to the touch, however as @DCContrarian mentioned.

However that would be the case if you heated the basement with forced air also. The same with the upstairs, the FA geo will not warm the floors, but still maintain a comfortable ambient temperature.

You can play around with that master bath radiant, as I expect it has forced air also?

With a slab sensor in the bath floor you can allow some heat to go into the floor even with AC running. Although you will be heating and cooling at the same time😳

If you set the AC at 76F the tile floor will be 76. The radiant could be set to maybe 82, so it hovers around skin temperature and has a neutral instead of cold feel to it.

The bath radiant could be on a setback control also to turn it off or down durning the night, save some energy. So you can manulipulate the two systems a bit.

DCContrarian

To the extent the space is already being heated, it is being heated by the geothermal. So taking hot water from that heat pump will not increase the overall heating load.