Any rules of thumb for using under-subfloor heavy aluminum transfer plates under areas likely to be carpeted?What are the considerations and expectations if this is done?How about the differences for doing this above conditioned space or unconditioned space?

A few simple thoughts...haha... the more wood you have above the tubing, the hotter the water temp you will need. Typically there is 2 runs per joist space (down and back again). If there is even the remotest thought that the flooring can be all new above and the subfloor is quite thick, it will be better to put the tubes on top.

You will always need insulation below the tubing if between joists. A radiant barrier and r20 of ROXUL is my method (but, I try hard to have people put the tubing on top if possible).

Are you able to calculate the loss of heat transfer to living space with various types of floor coverings and thicknesses?And if you are "blocking" the heat from where you are trying to get it to go,where is the heat going?

Every good radiant floor software program can calculate the heat loss of each room and temperature of the water needed to overcome the resistance of nearly any common floor covering available.

And if you are "blocking" the heat from where you are trying to get it to go,where is the heat going?

Nowhere, which is the problem. It stays in the heating system.

Some of the extra heat from having to use a higher water supply temp may stay in the heating system, but some may be completely lost because of the higher floor/outside temp difference which may result in a lower efficiency heating system. One normally doesn't want to use very much carpet (especially heavy carpet) on a radiant floor. And if you do, you normally treat the heavily carpeted area as "blocked" and you design for increased upward heat gain from the floor area that is "unblocked" to compensate and achieve the overall heat gain that is known/required from previously doing a room/building heat loss analysis.

So,do you find yourself thinking twice about radiant floors in bedroom areas and begin to consider panel radiators?

you should reconsider carpeting. it's an indoor air quality nightmare, not to mention a thermodynamic issue.

but if it must stay, it's another good argument for radiant ceilings.

NRT.Rob raises a valid point about carpet in general. I suspect people get hooked on wall-to-wall carpet from trac home experience where just putting carpet over subflooring wherever possible is a cheap solution for contractors. However, if you have a heated floor, there really is no need for carpet except perhaps for softer under-footing in some areas. For those areas, it is likely better to just use smaller area rugs…but be sure to account for the reduce upward heat gain in those zones if these area rugs are thick (i.e., have significant R-value). It is truly amazing what a skilled concrete person can do with acid etching/staining and stamps these days. There are also many beautiful tile options these days too.

When the floors are off, they can get cool, which is why granny darned those rugs in the first place. If our customers want carpet, they get carpet. But we like to know ahead of time and help them specify the type of pad and carpet for the best match with low temperature radiant designs. We have many carpeted designs that operate well below the condensing return temperature. Not ideal, but not a deal breaker either. Naturally, if carpet is in the mix a room-by-room Manual 'J' is mandatory and the carpet built in to the final design.

Sub-floor systems sans heavy aluminum plates e.g. Thermofin C are out of the question if carpet is the cover.

Frankly, we consider excessive carpet and hydronic radiant floor heating an oxymoron and heresy!

Yes, it is certainly doable if one doesn't mind operating at higher supply and return temps resulting in less heating system efficiency. One would certainly have to include this additional floor surface R-value in the design and one should always do a room-by-room heat loss analysis whether carpet is used or not. The only time the floor should really get uncomfortably cold is when you might want it to be cold...perhaps during the hot summer months. Even then one might still want to run some heat cycles to keep floor surface above the dew point if high humidity and floor condensation is an issue.

Good indoor air quality is something worth pursuing and one of the many benefits of hydronic radiant floor heating. We try to first persuade people to consider this before just jumping on the conventional excessive carpet bandwagon.

floor sensing eliminates cold floors as a comfort issue. carpet is a tactile or echo measure only in a properly controlled radiant floor heated home. and with the air quality issues, they should very seriously be considered for elimination by anyone who cares about health.

Agreed, we tend to over-kill floor temp sensing in our designs. However, it is easy and cheap to provision for multiple floor temp sensors per zone (i.e., put sensor conduit into the slab before the pour) to enable better control options (immediately or in the future). Closing the PID hydronic radiant heating control loop on floor and outdoor temp (actual and forecast) feedback is much preferable to using indoor temp in our opinion. There is a huge time lag associated with using indoor temp feedback and T-stats can only measure the localized wall temp resulting from the floor radiation they happen to experience and they do not measure actual air temp anyhow. The actual slab temp and rate of change provides better feedback if autonomous comfort control is the objective. Like carpets, one just needs to convince customers that T-stats don't make much sense for a modern hydronic floor heating system...sometimes not easy.

"When the floors are off, they can get cool, which is why granny darned those rugs in the first place."

Hooked those rugs, BB. Those darned grannies were happy hookers.

OK...

A standard room air thermostat properly placed in most of the radiant floor heated homes we design, (up to 5000 s.f. depending on the architecture) will keep the room temp within a degree. Just last week I disabled the floor sensor on a Tekmar 508 (the only control they had for the main floor) preferring to use the ambient sensor instead. After 3 years they are finally, and profoundly, happy with their radiant floors.

Over-control is not perfect control. With the right radiant panel for the load and weather sensitive supply water temperature control, expensive controls are a waste of time and money until you get into big glass or other factors which might demand extraordinary control or feedback.

adding a floor sensor is cheap. it makes sure the floor doesn't get too cold. the air sensor still works too.... if you improved anything by turning off the floor sensor, then either they turned off their air sensor, or they had a floor temp set wrong that was screwing them up. under NO, ZERO, NEVER circumstances would turning a floor sensor off IMPROVE comfort otherwise.

set an air temp. set floor temp min to that. set floor temp max to off. that's as close to comfort perfection as the rest of the system can deliver. and that's not "over control". it's cheap.

indoor feedback controls are now not that much more either... and they are much better. by any measure, in nearly every system. certainly if you are using mod/con boilers...

"under NO, ZERO, NEVER circumstances would turning a floor sensor off IMPROVE comfort otherwise." And they may not improve it either.

The ambient sensor was turned off (probably out of ignorance). Thank you for the refresher, it has been over ten years since I installed my first 508 I think. All the slab sensor can do is bracket the end of the slab in relation to the ambient control.

I am not against the use of a slab sensor, but the constant sales pitch and the misapplication of many makes me think most layman and most of my customers could live without them. In the big lake houses with walls of glass around Prior Lake or Lake Minnetonka here in chilly Minnesota we could use a lot more control than we generally get and occasionally I wish someone would have dropped a thermistor into a conduit, but it is one in 50 jobs in our high-end business.

they may be extraneous in some cases. moreso if you have a nice, constantly operating indoor feedback system. Much less often in any other case... maybe some zones don't need them, but most houses have zones that would benefit in most cases. again, unless they are all operating nice and consistently anyway.... a rarity I'd say.

misuse of technology is an issue, but why not just turn the air sensor back on instead of the floor sensor off? I guess I've met people who are better off with less, but most people are capable of learning "stop playing with the floor temp" at the very least.... aren't they?

OK, I will turn the floor sensor back on, next year on the annual, just for you :-).

Badger,what was going on during the 3 year period prior to them finding bliss?