Localized output to produce \"warm toes\"??

Hugh Mason

We heat our well insulated 1600 sq.ft.ground floor/2400 sq.ft total geodesic dome with only about 400 sq.ft of radiant coverage in the very interior ground floor of the house. I purposely ran the tubing alone the areas where we would stand or sit on the floor. The house is EXTEMELY comfortable and our plans to add additional radiant output have been shelved because we would hate for the currently heated foor to be cooler than it is. If you want a nice warm floor in certain areas and have a very low heat demand than you need to concentrate heat in the areas you wish to be warm. My wife and I love really cold weather because the floor is really snuggly at those times.

SciGuy

KW_2

Localized output to produce \"warm toes\"??

Question regarding tubing layout. I’ve been told that in very well-insulated buildings with smaller heat loads, in-floor hydronics may not produce a “warm toes” effect – the floor may not be warm enough or run long enough to create the effect. In a situation like this, if the warm toes effect is desired, is it possible or a good idea to concentrate tubing in a small portion of the room – which would result in running higher surface temps or for longer periods to satisfy the load? A couple of examples:


Kitchens: If you have a 140 sq ft kitchen (10x14) and cabinet run along two walls (covering 48 sq ft) and there is a 2x4 island (covering 8 sq ft) – you are left with the places where people walk and stand – leaving 84 sq ft of radiant floor. If this kitchen has a heat loss of 3000 BTUs, instead of 21 BTUs /sq ft for the entire floor area – you’d have to produce 36 BTUs / sq ft (not sure if this is even possible!)


Hallways: In a 4’ wide hallway, no one walks in the outer 12” on either side (at least judging from wear patterns in carpet!). So why not place the tubing at a spacing down the center of the hallway?


Does this approach make sense – concentrating output where the occupants are most likely to be?

Brad White_19

Makes some sense at first

to the extent that the higher output areas are factored into the entire heating output, so you do not over-heat the space in the process.

But then my concern is the perceived uneven temperatures going from one area to another in the same room.

In kitchens I think it makes sense to not heat below cabinets except where you may want a buffer for freeze protection. Otherwise murder on root vegetables Perhaps the concentration will be sufficient to meet the load and you are done. You may push it but should be able to get over 36 BTU/SF depending on floor finish.

Brings up the conundrum of tile versus wood. Tile can in my experience feel cooler because it is more conductive than wood at the same temperature, yet warm tile is more appreciated, probably because of the expectation. Now you got me thinking again.....

Ericjeeper

I am no expert

But a couple things I can toss in from my limited own house experiences.The first season, I was sending out 120 degree hot water. and I noticed the largest area on a single loop,. My bedroom 18x18 would heat the outside four feet of the slab up to lets say 80 degrees and then the thermostat would be satisfied..
Now I have a mixing valve in.. I am only sending out 92 degree water and I am experiencing a more even floor temp.much to my liking.I have to manifold locations.. One in the garage with eight loops.. four for the garage, and another four for the great room 22x40, and another manifold with 7 loops. in a closet centrally located in the house. all my tubing to the four bedrooms and bathrooms. runs down the hallway.. it stays toasty even though the returns run in the same hallway. I figured the returns would cancel out the supplies.. but there are times when my delta T is very minimal. due to only one or two loops calling for heat at a given time.,
If you use a manifold with a flow valve you can control the flow rate.. I should turn the rooms down that heat up quickly.. but I figure the lower my delta t. the less I am reheating the supply water. good luck and sorry I could not be of any help, to your original question

[Deleted User]

Following up on this theory then...

it would make sense to have the highest density tube be in the middle of the room instead of the exterior of the room as it typically done.

This follows the vein of thought that the highest water temperature potential is in the beginning of theloop, hence tubing at say 18" OC near the exterior walls, and as the fluid cools, increase the density towards the interior part of the complex to say 6" OC.

I've often wondered what a heat loss calculation would look like if it were perfromed in sections of 1 foot bands from the exterior to the interior. Kind of like an MRI.

Slices of loss calc anyone??

I had a former employee who was dyslexic and put a loop into a 3 sided room once backwards. In other words, the hottest water was delivered into the core and the cooler water was at the exterior. It was a straw bale home with non electric TRV's. and the consumer never said a thing. Course, I didn't tell him about the fauxpaux... My bad ;-)

ME

brucewo1b

Why not keep the floors at 70 degrees with a floor sensor and increase temp when additional warmth is needed. That way the floor joist space is at least seventy at start and the floors are always at least 70 and when room temp is above seventy they should not be adding heat to the room. Maybe I am all wet but that would seem to help.

Wayco Wayne_2

A quick comment

abouts Brad's comment about not heating cabinents that will contain root veggies. I have also been told not to heat any pantrys that have any flour products stored in them because a warmed space will hatch the flour bugs contained within and severely shorten the shelf life of these products. (ewwwww!) WW

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Unknown

20 BTUs/sq ft is not a low load. That's an 80 degree surface temp at a 70 degree room temp. Go ahead and skip the counters anyway, but for other reasons.

In other areas, you generally do not want variable floor temps. Either for wood or for occupant comfort. You want the floor temps even.

In low-load situations, that's when we start looking harder at radiant ceiling. Much cheaper, very effective, and if the floors aren't going to be very warm anyway, why spend more to put the heat there?