pex layout advice please

logboy

1st off, thank you for any advice. I have a few questions while my drawings are in getting a heat loss calculation. My building is approx. 1000 sq ft, log construction (an average 13" dia. spruce logs) with 2 inside wall logs of the same dia. The crawl space has 4" XPS rigid insulation attached to the foundation walls and along the rim joists with all gaps foam sealed. The dirt floor has 15 mil vapour barrier taped up the walls to the xps.
I hope to install radiant heating under the subfloor.
Is it alright to run the pex under where the interior log walls are?
Along the exterior walls, should I double up or have the 1st 2 rows closer together and then go to 8" spacing?
Would it be crazy to have the full 1000 sq ft on one zone (not having loops longer than 300 ft) when there is a great room (approx. 470 sq ft with a 19' high cathedral ceiling) .... the under the loft area (ceiling height 8") has a 205 sq ft bed room, and approx. 241of kitchen / bathroom.
I hope my questions make sense and thank you again for any advice. Jim in Zone 5

hot_rod

If you are having a heat load and design done, it will spell out the tubing layout

If not you need to get the individual room loads and calculate how much tube the rooms need

Money well spent getting a radiant design done by an experienced designer, it’s the road map to a successful installation 

Mad Dog_2

Listen to Hot Rod he knows...My radiant quirks would be to go with 6" Spacing in some areas for greater warm floor coverage and so you NEVER get a cold spot.  I never have.  As A rule,  you try to avoid tubing under wood furniture; cabinets,, toilets,, refrigerators et cetera. and maybe an interior log wall UNLESS your BTU demand is THAT  CLOSE and you need a little extra umph.  Just always keep track of your loop lengths as your installing it so you don't over run the max distances or have grossly different loop lengths. Mad Dog. 

logboy

thank you for the speedy replies.
When i had the heat loss calculations done for my garage couple years ago (I needed the heat loss for city permits), there was no design for pex lay out. Maybe it will be different with a cabin with rooms and loft. I'll make a point of asking.
I like that the pex has markings on it to let you know how many feet you've laid and yes, I'll make sure my loops are under 300 ft each and all relatively close in length.
jim in zone 5

hot_rod

never any harm in over tubing, other then cost. It allows for the lowest possible supply temperature. source.

The risk you run is underperforming on cold days.

With log homes the killer can be infiltration, especially as there logs age, dry, crack twist, etc. One thought is a blower door test when built, then a few years down the road.

Mad Dog_2

I remember in my very early days of installing A radiant floor for a large, fully glassed, tile, hard to heat  vestibule.  I thought about it.   If I layer and "stack" several levels of pex over eachother, I'll meet the heat loss load, no problem!  Before I did it, I ran it by the Great Slant Fin trainer and all around nice guy, Jim Earhardt:  He smiled and said, " I understand your concept and attempt, Matthew, but Radiant doesn't work like that...the 100 degree water is only going to warm a slab to a certain temperature point, and that's it, you'll max out!'  In short, he imparted to me that some rooms might need supplemental heat when radiant alone can't meet the heat loss. Jim's Greatest value is that he had run his own small business and had tons of hours logged installing and troubleshooting.   Mad Dog

Mad Dog_2

Slant fin had top-notch instructors. Jim Earhardt, Larry in Tech Support, Noel Murdough, Amir Amir.  I would call these guys with unrelated crap all the time, or just to chat.  Brilliant and fine men!   Mad 🐕 Dog