Radiant floor heating plan help

Lynyrdskynyrd_01

Hello. I am in the beginning stages of planning a house. It will be 1,950 sq ft single floor and would like to know the best way to go about installing a radiant floor heating system would be. I need to have the pex planned so I can pour the slab. Then figure out what the best heating element would be for me. I've been looking into boilers and combi boilers. Do I need to have the heat loss calculation done before the pex or is that before the heating element? Also any info on the slab insulation and pretty much everything I need to have together before pouring a slab, then I can work on the system once I get the house built in the dry. Any help would be much appreciated. Thank you.

hot_rod

Two steps are the heat load and the design which includes the tubing layout. This downloadable manual takes you through all the steps.

https://www.uponor.com/en-us/customer-support/order-manuals

I recommend all slabs get the tube installed 6" on center. Keep the tube 2" below the top. This allows for the lowest possible supply temperature. So you have high efficiency boiler or heat pump compatibility.

Use a 6X6 mesh for to tie the tube down.

Here are some tube layout options. The bifilar is a nice pattern, not so many 180 turns to tie down.

Also pics of my shop with 6" tube spacing.

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Lynyrdskynyrd_01

Thank you so much. I've been searching the better part of a week for something like this manual. Theres really not a lot of information on these systems at least that I can find. This seems like a very efficient heat source. From everything else I have gathered I would be best off running mini splits for ac? Also how much insulation is under the slab in your shop and do you recommend more or less based on your experience?

Looks like I have a lot of reading to do before I have much more questions.

hot_rod

2" foam, closed cell like Owens Pink or Dow BlueBoard.

The edge insulation is a big deal, and if it is a slab on grade that is a tricky detail to cover the top edge. Usually a metal Z flashing under the siding to cover the top edge of the foam. Then edge foam should go down to frost level. May be a detail in that guide.

Yes to mini splits for AC or shoulder season heat.

Take pics of the tube layout for future reference. A drone is great for that.

Good for you for getting opinions before you start. So many bad installs come by here that could have easily been prevented.

hot_rod

another good design guide.

https://www.rehau.com/downloads/497804/radiantheatingsystemsdesignguide-855601-rehau.pdf

DCContrarian

I'm not a big fan of concrete slabs.

You'll get better comfort if you have a system that is highly responsive, which means that it is quickly able to change its output as the heating load changes. For that you want something with minimal heat capacity. If you look at a system like Warmboard that's their big selling point.

Also, concrete just makes for a lousy residential floor. It's hard, it's noisy, it damages easily and is hard to repair.

To @hot_rod 's point, a system like this has to be designed. You can't just throw tubing down and expect that it will deliver comfort. We get people here all the time trying to make systems work that were just done wrong, I call them "designed to disappoint."

Lynyrdskynyrd_01

@DCContrarian so it is basically the same exact system but run in a subfloor? Do you have any personal experience with it and is it efficient enough for my main heat source like the normal radiant systems?

hot_rod

their are “dry systems” that can go under or on top of subfloors. They work as well as slabs as far as heat output. The under subfloor will need higher supply temperature. Less suited to A2WHP use.

Pros and cons to slab radiant, the mass can be a helpful storage. Nice consistent temperature. Slabs can work nice with passive solar gain.
The slab is both the structure and the heating system.

If you are in an area with frequent and wide temperature swings, the light or dry systems are easier to control.

I have had two homes with slab radiant. We had hardwood, tile, and a few throw rugs as floor covering.

My office had a slab that we colored, put the powder right in the trucks to mix. I did several homes for concrete contractors that colored and stamped their slabs.

Slabs are easy to clean a slab, especially for pet owners🐶

Personally if I were to build an efficient home , which you should, with heat loads in the teens or single digits, I would skip the radiant floors and use panel radiators, maybe an electric radiant in the master bath.

Or heat emitters that could heat and cool.

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1840656#Comment_1840656

I assume by "efficient" you really mean "effective," in that it's capable of keeping the space at a comfortable temperature.

First, it's a huge mistake to assume that "normal radiant systems" are automatically effective. We get people here all the time who made that assumption and now are looking for fixes to make their ineffective system effective. There aren't easy fixes, it's much better to design a system from the get-go to be effective.

The key to a heated floor being effective is for it to provide enough heat to match the heat loss of the room that it's in and keep the room comfortable. The heat loss of the room is determined by the construction of the room and the climate. This can easily vary by a factor of ten, there are no useful rules of thumb and be suspicious of anyone who wants to design using rules of thumb rather than measuring the room, analyzing its construction and looking at climate data.

The amount of heat that a floor puts into a room is entirely determined by the difference between the surface temperature of the floor and the air temperature of the room. There are two common extremes that lead to dissatisfaction with the comfort. The first is if the heating load is so high that in order to meet the heating load the floor has to be so hot that it is uncomfortable to stand on. This problem will be exacerbated if the floor is made from a material that doesn't conduct heat well, because then the floor will have hot and cold spots. The hot spots will be uncomfortably hot and the cold spots won't be putting out any heat.

The other issue is less serious, it happens when the heating load for the room is so low that the surface temperature of the floor has to be so low that it is not perceptibly warm. In the past 20 years or so there has been a dramatic improvement in what is considered acceptably insulated and air-sealed in residential construction, new houses built to the latest standards use a lot less energy to heat than in the past, and this situation is not uncommon in new construction.

Since the floor temperature controls the heat output, you want the floor temperature to be able to change as quickly as the heat load changes. If you have a room with a lot of solar exposure the load can drop precipitously when the sun comes out, and fall just as quickly when it goes away. A floor with low heat capacity will give better comfort.

Concrete conducts heat well, but has fairly high heat capacity. A system like Warmboard combines a layer of high conductivity aluminum with lower heat capacity, to give even heating and better responsiveness.

I'm not endorsing Warmboard specifically, it's just the best-known brand in that space and has almost become generic.

Lynyrdskynyrd_01

The way I worded that did sound like effective but I was also wondering about effeciency as in cost to run it effectively. I do prefer a slab also.

Lynyrdskynyrd_01

@hot_rod I guess the better question since your talking specifics is should I go with the radiant. I have a moderate temp yearly avg is high 60s. The winter normaly gets down to low 20s and summer gets around 100. I know you dont need to be jacking with the thermostat a bunch with radiant and i wont be. So I guess im asking if you would indeed recomend radiant for my circumstances?

hot_rod

If you like a unobtrusive comfortable system it may be worth the money. Even you you don't get the warm floor feeling all the time, the space will still be comfortable. Get the home defined better, see what the heat load comes out at. That would help make the decision, for me.

Panel radiators are a radiant system also. The move the heat to any object in their line of site. Easy and fast to control, some really creative designs. I put radiant in my concrete counter tops :)

As far as efficiency. There are a few efficiencies involved. First and most important is the efficiency of the structure. The better the build, windows and insulation the higher the efficiency, the lower the heating and cooling cost. That is a gift that keeps on giving.

The efficiency of the heating and cooling equipment itself.

The efficiency of the distribution system, getting the energy from the heater to the space.

I'd certainly let mother nature help, facing south with some proper passive design and shading is a nice thing to consider.

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Lynyrdskynyrd_01

I will have tons of shade and a slight rise in the land to the north and I plan on doing really good insulation regardless of what heat source. I was trying to decide on how to do the radiant heat before finalized plans so It would work with my floor plan but your saying I should really get a finished plan to really figure out my best way to go about it then work in the system? I also haven't thought about counters is that its own system?

DCContrarian

I like to say an ounce of insulation is worth a pound of hydronics when it comes to comfort.

hot_rod

really the shell itself determines the heat load, not every room needs to be exact, to do some preliminary load calculations

The wall construction, window and door sizes, roof insulation, etc. The more info you have the more accurate your numbers will be