Hi there, I have a staple up project, about 1,800sf area, mostly hardwood. I plan to use heavy gauge (extruded) aluminum plates. The floor plan has some areas which doesn't demand much heat (kitchen counters, island, closets, etc). Also there is a large (and very warm rug) in the middle of the living room. I'm concerned about: - $$$ spent on extruded plates where I don't have to - Outputting same BTUs/sf under rug as on bare hardwood floor may overheat the floor under rug So, I think to use extruded plates everywhere except those areas. In those areas I plan to use lightweight "omega" plates to support the pipe and still output some BTUs. The light plates will be spaced out, while extruded ones would be put closely to maximize heat transfer. Any thoughts? Reasons not to do it this way? Thank you in advance. PS. Yes, I'm sure the rug would be there for long-long time considering how much $ my wife invested in it. LOL

I like the idea. I would put the thicker plates in the walk paths and anywhere you will be standing.

What is the thickness difference between the two plates. Is there really a difference in heat transfer.

A similar technique can be used where a radiant floor won't be as warm as desired (ie, comfortable with bare feet). Omit all plates in some areas so that other areas can run hotter.

Plate coverage matters. A full coverage thin plate should significantly outperform a partial coverage (narrower) extruded plate.

http://www.healthyheating.com/thin-plate-versus-thick-plate.htm

The difference is in the quality of the contact area between PEX and plate. Then again between plate and the sub-floor.

The "comfort" performance of either is questionable since the relative term "warm" varies along with the heat load for a particular room, the weather and the control system with the various options.

The proper way to design such a system is with a dedicated software program e.g. Wrightsoft using the appropriate design module allowing you to model all available technologies. Though the "warm" rug may not be an area of concern, you may need the slightly reduced output to satisfy the heating load for that room. Any competent designer will tell you than radiant panels are not used under cabinets or the frig but that the reduced floor area often requires extra attention since the floor area determines the potential output of the floor panel. Many kitchens have to have a supplemental heat source, best determined by an accurate heat load.

The current science is over 30 years old. Why guess?

Badger, the room with the big rug would have to be heated more to compensate for the insulation qualities of that rug. I don't think the rug is going to decrease the heating need, only increase it because the heat can't get into the room because it is blocked by the rug. The heat load of the room is not going to be changed by the rug, so the floor that is not covered will have to heat more to makeup.....I am not a rug fan....

Like I said.

You have to allow for the decreased output of any covered radiant panel according to the resistance of the rug in this case.

I love rugs and am not afraid of carpet either. The difference in output can be critical in retrofit situations where the design temperature of the floor may bump the excepted maximum of 86°F or the optimum output of the heat source e.g. heat pump of condensing boiler, but this is not always the case.

Thus the need to know what your doing.

All, tnx for your replies.

Badger, I don't see much points in calculating or modeling anything. I don't even have to much heat loss, I have perfectly working central air in the house, so if on cold night radiant floor alone cannot keep up , the central air will kick in. Actually I think to run it anyway once a day - besides heating it moisturizing the air which is great.

Why do I need radiant floor? Because it's awesome! I done it in my old house, my wife loved it so much, she wants it in the new house too.

Either plates, extruded or lightweight, will to the work. But I want to go with extruded plates to lower water temperature further.

I don't see why bother with calculations if I can build the system 1st, then eхperiment with it and tune it up to the settings I like. I realize it's a heresy to say on HVAC forum. It may be especially strange considering I'm an architect. But hey, it's not a paid project, but my own house - why bother with preparations?

So, back to my question - my rug concern is not about total BTUs output to the area. But running 100F or so water through extruded plates with insulation underneath and rug on top will bring the hardwood to (let me guess) about 90F, which may start warping the solid wood planks over time.

So, less output under the rug to keep the hardwood floor temperature about the same under the rug and around it.

Makes sense?

PS. Dispite my heresy thohghts, I did room-by-room heat loss calcs.
PPS. Yes, I know 90F alone will not actually warp wood or do any damage to it. it's mostly the moisture content fluctuations issue, not temperature. But still....

If the HR is supplemental, you might want to place slab temp sensors and just heat floor to desired temp. 85F is the maximum recommended temp for most rooms. 90F is okay for bathrooms. We have free HR design software on our website should you want to sort out loop flow rates, temps accounting for rugs.

You have a floor describe a floor "warming" system. A heat load is not needed. Controls are the key to comfort.

I have recorded the 3/4" solid oak floor in front of my fireplace at 115°F and yes the boards separate in winter. 90° is not unusual or extreme. It is all about the moisture content.