Hi Guys, I am getting ready to start to plan out a radiant heat system for my house on Long Island. How would you go about specing out a system like this? What information do you need? Thanks, Pat

Tube spacing is usually something on the order of 8-12 inches. If you have EXTREMELY large spaces (generally commercial) to cover, and don't mind less even heating, you can go further apart.
You can also go closer together, but, generally, you don't want to go below 4 inches. And that'd be a LOT of PEX tubing!
If you're using a system like WarmBoard, the spacing's all pre-determined.
If you're doing in-slab, there are foam-board spacing systems. This'll provide the sub-slab insulation you'll require to NOT leak most of the paid-for heat directly into the earth.

Warmboard: https://youtu.be/qkDwctBQfY0

Nudura HydroFoam (Under-slab): https://youtu.be/mPCANjpC31Y

Posted By Dilettante on 01 Feb 2019 02:12 PM
Tube spacing is usually something on the order of 8-12 inches. If you have EXTREMELY large spaces (generally commercial) to cover, and don't mind less even heating, you can go further apart.
You can also go closer together, but, generally, you don't want to go below 4 inches. And that'd be a LOT of PEX tubing!
If you're using a system like WarmBoard, the spacing's all pre-determined.
If you're doing in-slab, there are foam-board spacing systems. This'll provide the sub-slab insulation you'll require to NOT leak most of the paid-for heat directly into the earth.

Warmboard: https://youtu.be/qkDwctBQfY0

Nudura HydroFoam (Under-slab): https://youtu.be/mPCANjpC31Y

Thanks for the information. I am going to be starting out with two rooms (bedroom and bathroom) initally on the first floor using aluminum plates from underneath in the basement. I eventually plan on doing radiant on the entire first floor as well as the 2 bathrooms on the second floor. Currently I have a gas boiler heating radiators and a gas HWH for the domestic water... Any advice on how I should go about specing out the mechanicals would be greatly appreciated...

First you start with a room-by-room heat loss analysis (ACCA Manual J8 or ASHRAE equivalent). With that information you can starting designing the HR parameters (PEX spacing, PEX circuit lengths, flow rates, and supply temperatures) that will provide the required room-by-room heat gains. Then you can size the circulation pump and heat source. John Siegenthaler’s “Modern Hydronic Heating” describes the design and installation process in great detail. We also have free DIY calculators and information on our website to accomplish the heat loss analysis and HR design if you are so inclined. Otherwise, hire someone who is licensed and qualified to do this which is hardly ever a plumber or a component retail vendor.

What sailawayrb said- all heating projects (not just radiant) need to start with the load calculations. Shooting from the hip can get spendy, may end up with unsatisfactory performance, or both.