How much pex for inslab heat.
 

!,200 sq ft house, hope to put in the floor next season. Will be 2 inch concrete, planning 2 0r three loops,
1 living room,
2 2nd bdroom, bathrm, & utility rm
3 master bed.
May combine 2 & 3 since they are adjacent and take up about 1/2 the house.
House is pretty well insulated & about 1/2 bermed on 3 sides in Zone 4.5
Plan on using 1/2 pex. May use outside wood boiler, or nat gas hot water heater for heat.
1000 feet of pex is not that pricey so am wondering what experience there is here to indicate total requirement for 1.200 sf.
Any links to sites that will calc it, would be appreciated.

nib

I used 1 ft centres for 5/8 ID tube as that was the tech available. 1/2 pex. will be perfect on 1 ft. centres. So for your calculations 1200 Lin ft. and really its quite in-expensive. Are you planning a slab build or a gyp-crete overpower (self level) on subfloor.

Don't over zone, 1 thermostat controlling the slab temp. and 200-250 ft loops.

I've built mine on slab and heated floors are awesome. Some here have eluded to in-floor being expensive but I've ran the numbers for other requests and they are less than duct-work especially if your doing the grunt work.

If I were to do it again I would run two pex systems 1/ for your outside wood or gas fired boiler and the 2/ for solar hot water. This saves the cost of a heat-exchanger and efficiency losses. We have solar hot-water heating the floor and some yrs it supplies 1/2 our heat load. The solar hot water would heat your floor directly AWESOME!!!

Randen

nibs

Where are you located? The total heat load, slab thickness, etc are all dependent on how cold you get!


Steve

Your local temperatures will have a lot to do with your results.

2" slab is pretty thin. Spacing your PEX at 12" centers will not give you very even heating of your slab.

If your location is such that heating efficiency is not critical, it won't matter much. If heating is a serious issue, you will want to be much smarter about your project.

-AC

"House is pretty well insulated" indicates an existing house, so probably an over pour on a wood subfloor?

"Zone 3.5" gets pretty cold a times.

I would recommend R20 under subfloor. Bond-breaker plastic on top.

1/2" O2 barrier PEX-A on 8" centers (to minimize hot/cold bands), so 1,800' in 6 loops (300' max per loop) with Sioux Chief copper manifolds with 3/4" pex feeds, one manifold of each pair needs to have the 1/2" pex ball valves to allow air to be pushed out by water, 1 loop at a time).

Clamp pex down with 1 screw clamps as it will try to float up.

3x thermostats controlling 3x 3/4" zone valves, 1 Grundfos Alpha pump moving all the water.

The floor will be slab on grade,
from the bottom, waterproof membrane, 2 or 3 inches of epscrete, 2 or 3 inches foam insulation, pex piping, and 2 possibly 3 inches of fiber entrained high strength concrete.
Am building in zone 4 and much of the house is bermed, we have been
making tilt up ferro cement walls for much of the exterior and most of the interior walls. All the walls are on their own footings on 2 inches of foam.
AC I have no problem making a slab 2 inches thick with a compression strength of 6000 lbs, using high cement content fly ash, fiber and low water content. & have worked in construction for about 40 years starting as a laborer, then carpenter, then foreman/superintendant then consultant.
My biggest problem is that in my mid 70's am not as spry as once was.
I hope to get the second half of the house closed in next season and if we are able may start laying the floor. You seem to be quite critical of some of my posts, please recognize that I have at least a year to finalize my floor design so don't worry.

I do not worry about your slab.

My comment relates to the significant thermal variation in a two inch slab that will result from 12" PEX spacing.

If you are interested in a very high efficiency floor, you should reduce the spacing.

At your age, efficiency will never pay for itself, unless you take into consideration benefit to subsequent owners.

-AC

P.S.: Don't whine about your age... I'm older than you.

"I'm older than you."
Then act your age and drop the insults.

The tiny amount of insulation used in the US building industry is amazing from a European perspective.
In Europe nobody would consider putting less than 150mm of PUR insulation beneath a heated slab and even unheated, most of that would be required just to meet building regulations.
Our own standards took a long time to get to this level as the construction industry is conservative and slow to change.
Why not learn from our mistakes and start insulating to a high standard?
Surely foam is cheap?

If you have to heat your house like we do (in the Netherlands 55°North), I would suggest to make the distance between the tubes much smaller. This causes a lower required water temperature in the tubes. In that case your floor is ready for future use of a heatpump. Or if you heat with gas, the efficiency of your boiler is increasing, because of more condensation from vapour in the flue gass. I have 6" spacing (built in 1987) but with the heatpump we have since 6 years, I would have liked 4"spacing. Every °C that the water in the floorheating system can be reduced, gives me around 2,5% extra efficiency of the heatpump.....