Hi, I'm working on building a masonry house in southwest Colorado, and I'm looking for advice on radiant panel design for the floors. The CMU walls will have insulation on the interior, and we'll have foam insulation under the slab. Also, the house is designed for passive solar and bermed up a little on the north side. The property has a lot of solar gain - we're on the south facing slope of a desert canyon, and we get quite a bit of sun during the winter. I'm new to working with PEX tubing, so I'm not sure how to go about sizing the system or designing the tubing runs. Any advice would be appreciated. Thanks, Cliff

How insulated is the house going to be?

R20 houses loose a lot of heat so the heated floor will have to make up for that heat lose and feel nice an toasty to yo feet.

R30 houses don't loose much heat so the floors wont be warm. Maybe only 5-10 degrees warmer then your therm setting.

I feel radiant floors are a big expense that don't have the pay back they used to. I have built and lived in 2 all radiant floor houses. This is what I found.

Some other notes. CMU, you are better off having the insulation on the outside of the wall. You have a lot of solar gain so if you don't have a large mass to absorb that heat or the house is going to turn into a sauna quickly.

Good luck, tell us more about the house design.

Before you can accomplish either a hydronic radiant floor heating or a passive solar cooling/heating design, you first need to accomplish a room-by-room heat loss analysis (e.g., ACCA Manual J or ASHRAE). We have found the best book for hydronic radiant design to be John Siegenthaler's Modern Hydronic Heating. We have found the best book for passive solar cooling/heating design to be Edward Mazria’s Passive Solar Energy Book (Expanded Professional Edition).

In order to properly design either a hydronic radiant floor heating or passive solar cooling/heating system, you need to have the heat gain provided by each system align with the heat loss of the building. That is often easier said than done and involves accurately determining all the associated Btu/H quantities that need to be aligned in lieu of just blindly trusting design "rules of thumb" that are often casually paraded about. Here are some samples of hydronic radiant floor heating and passive solar cooling/heating designs that may be found on our website:

https://www.borstengineeringconstruction.com/Sample_MJ8_HR_Design.pdf

https://www.borstengineeringconstruction.com/Sample_Passive_Solar_Analysis.pdf

We also have free DIY calculators on our website that can be used to accomplish hydronic radiant floor heating and passive solar cooling/heating designs:

https://www.borstengineeringconstruction.com/Heat_Loss_Analysis_Calculator.html

https://www.borstengineeringconstruction.com/Hydronic_Radiant_Floor_Heating_Design_Calculator.html

https://www.borstengineeringconstruction.com/Passive_Solar_Altitude_Angle_Calculator.html

https://www.borstengineeringconstruction.com/Passive_Solar_Roof_Overhang_Design_Calculator.html

https://www.borstengineeringconstruction.com/Passive_Solar_Fenestration_Exposure_Calculator.html

https://www.borstengineeringconstruction.com/Passive_Solar_Heat_Gain_Calculator.html

https://www.borstengineeringconstruction.com/Passive_Solar_Thermal_Mass_Performance_Calculator.html

The associated instructions for each calculator explain in detail how to use the calculator and also explain and walk you through the hydronic radiant floor heating and passive solar cooling/heating design process:

https://www.borstengineeringconstruction.com/Calculator_Instructions.pdf

So maybe start with the instructions and the books to first get educated on these subjects and then either delve into the designs yourself or hire someone to do them for you. I normally recommend using different/independent parties for the heat loss analysis/design versus the installation so as to avoid “catalog engineering” and over-sizing equipment.

I fully concur with Newbostonconst in that hydronic radiant heated floors in energy efficient homes DO NOT normally feel warm. However, the floors NEVER feel cold either. I also like the fact there are no unattractive registers, no sound (noise) and no moving air (drafts) associated with hydronic radiant heated floors. And hydronic radiant heated floors are often the lowest cost heating solution option for new construction when you are already planning to have concrete floors. And if you are thinking of not using concrete floors, maybe you should reconsider this. Wood floors tend to creak in general and when you heat them with plates and PEX, they creak even more.

And YES, you will likely need interior thermal mass in your passive solar cooling/heating design. But you will need the proper amount of interior thermal mass...NOT too little and NOT too much either...