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Power Boost to Floor Heating #54712 08/06/05 12:10 AM
Joined: Aug 2005
Posts: 11
Jamesnz Offline OP
Junior Member
I have a project in hand which involves a 500W 230V. ac heater coil bathroom floor installation that does not do the job it was intended. ie It barely reaches 21C. Apart from lifting the tiled floor and starting again I am going to use a "Buck - Boost" transformer setup to increase the heating output by using a 285V ac input to the circuit instead of the normal 230V. mains. From my calculations ( with the heater coil at approximately 105 Ohm)this should up the present current reading from 2.1A to around 2.75A giving a wattage of roughly 770W.I would be interested if anyone else has done this and how far can one go ? The transformer I am going to use , when it arrives, is a 230V ac to 55V. ac.

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Re: Power Boost to Floor Heating #54713 08/06/05 02:01 AM
Joined: Mar 2005
Posts: 1,803
Alan Belson Offline
Before you do anything, run the system up and measure the actual floor surface temperature. Once it's stabilised, if it's around 35 degrees C (95F), you are already at or near the limit. A higher floor temperature, created in an attempt to boost performance, might make walking on the floor in bare feet a distinctly unpleasant experience, if not dangerous to babies and pets. Depending on the cover material over the heater element, its temperature may already be close to the limit too, and it may even have a thermostat buried with it, which will negate all your plans. I'll let my betters here comment on the electrical implications, but my gut feeling is that this is a bad idea.

PS. Noticed you stated a 'tiled floor'. You can expect a maximum performance of around 10W per sq foot, (100W/M2) on ceramic/cement flooring, less on wood/plastic.

[This message has been edited by Alan Belson (edited 08-06-2005).]

Wood work but can't!
Re: Power Boost to Floor Heating #54714 08/06/05 02:12 AM
Joined: Oct 2004
Posts: 803
mxslick Offline
I see a fire or injury in your future....your best bet is to consult the manufacturer of the heater coil. As Mr. Belson has suggested, the heater most likely has an imbedded thermostat which will simply cut power to the heater faster if you try to boost the voltage. That assumes of course that the heater doesn't instantly burn out from the excess voltage.

I would think that since it's tile above, the type of tile cement is crucial for proper heat transfer. You may end up having to lift the tile anyway.

What about the floor itself? Is it open on the underside? (like a second floor or built over a basement/crawlspace?) Could you insulate the bottom side to help avoid heat loss?

Please, consult the manufacturer, there are too many risks associated with your idea, and it would be unfortunate if someone got hurt!

Can you post the name of the manufacturer here as well?

Stupid should be painful.
Re: Power Boost to Floor Heating #54715 08/06/05 02:35 AM
Joined: Aug 2005
Posts: 11
Jamesnz Offline OP
Junior Member
Thanks for the replies. To answer, the installation is on a cement floor and the best it can do re the surface temperature is, as mentioned, only 21C.

Re: Power Boost to Floor Heating #54716 08/06/05 03:05 AM
Joined: Jul 2002
Posts: 8,354
Trumpy Online Happy
Welcome. [Linked Image]
What I'd be interested to know is how you're going to interface a 55V transformer in with the 230V mains?, to derive 285V.
What sort of a thermostat and controller are you using on this system?.
Besides, a 500W element is just that, it won't dissipate any more energy than what it is designed for.
This set-up sounds like it could easily end in tears to be honest. [Linked Image]
I'm not aware of any underfloor heating elements that would enjoy being subjected to that sort of over-voltage and I'm pretty certain that that would instantly void any warranty in place.
Additionally, this type of heating system is required to have RCD protection.
I could be wrong, but 500W should be more than enough to heat the largest of Bathrooms.

[This message has been edited by Trumpy (edited 08-06-2005).]

Re: Power Boost to Floor Heating #54717 08/06/05 04:15 AM
Joined: Mar 2005
Posts: 1,803
Alan Belson Offline
Just looked up some data from my underfloor heating manual. For 100W/m2 emission, from a cement based floor, with ceramic tile over, the surface temperature should be around 28C, so you are low. The type of tile cement is critical for performance, as mxslick says, there are latex-rubber based flexible versions which will give poor heat transfer- a cement based product is best. An under-element insulation layer is vital, ( I bet this is your problem), or you will be warming the worms, [a few inches down, the earth's temperature will be 10C (50F), a massive heat sink].
My set up is hot water-pipe based, with a design heating of only 50W/m2, (wood floor, cork tiles over). The design floor temperature is only 23C so we are fitting supplimentary electric towel-rail heaters in each bathroom, using the floor as background only. If you want keep the aesthetics of a room uncluttered by radiators, rails or radiants, I'm afraid lifting the floor tiles may be the only option, since it seems you may need to put in a better insulation layer under. Also, for any underfloor heating to work properly, due to low emmission power per sq foot, the wall/ceiling insulation has to be really good too, R = 2.5 (metric) minimum = 100mm (4") of glass-wool minimum. Better is the new reflective foil multi-layer stuff, 7mm (0.28") thick is supposed to = 6" of rockwool but it's expensive. One thing all underfloor systems have in common is they don't work well in excessive drafts, ie. a ventilation fan tends to spoil the effect by dragging what little power you have outside to heat the sparrows! Since my guess is youre DIYing this project, get the floor tiles up, or improve the insulation and/or fit a heated towel rail and put this down to a learning experience, but leave the electrical stuff strictly conventional.
Stay safe,

Wood work but can't!
Re: Power Boost to Floor Heating #54718 08/06/05 08:37 AM
Joined: May 2005
Posts: 706
Tiger Offline
Check the manufacturers specs. and stay within the voltage range given. If you go to the top of that range you may boost the output.

I suspect that the concrete floor is sucking all the heat away from the system. I'd consider adding electric baseboard heat before tearing out a tile floor.


Re: Power Boost to Floor Heating #54719 08/06/05 09:12 AM
Joined: Sep 2003
Posts: 650
winnie Offline
Quoth Trumpy:

Besides, a 500W element is just that, it won't dissipate any more energy than what it is designed for.

Most of the heating elements that I've come across are simple resistors, dissipating power at E^2/R; bump the input voltage up 10%, and the power dissipated goes up by 21%.

A 500W element is _designed_ to dissipate 500W. Increase the input voltage, and the power dissipated will increase, but the element may not be able to _safely_ deal with the increased power dissipation. Increased power dissipation generally means increased temperature, which means reduced component or insulation life.


Re: Power Boost to Floor Heating #54720 08/06/05 01:53 PM
Joined: Jan 2005
Posts: 5,316
renosteinke Offline
Cat Servant

I caution you for two reasons.

First, most products are intended to be used with a supply voltage no more than 10% over the nameplate voltage. You propose to exceed this.

Secondly, such systems are to be GFCI protected. Your GFCI would be the breaker supplying the tramsformer- and I fear the transformer will prevent it from protecting the circuit. Should you place it after the transformer, you will be exceeding the voltage it is designed for as well.

You'ld be better served by installing a recessed light in the ceiling, with a heat lamp bulb shining on the floor- assuming, of course, that this is outside the shower area!

Re: Power Boost to Floor Heating #54721 08/06/05 04:22 PM
Joined: Aug 2005
Posts: 11
Jamesnz Offline OP
Junior Member
Thanks for the all the responses so far. To explain to you all further ...The original installation was made during an extension to an existing house. The area in question is roughly 5M sq. or 57ft. sq so a time clock operated 500 W underfloor heating element should have been ample. The bathroom is properly insulated and there are no drafts or such. I personally watched the installation which was carried out according to the manufacturers specifications. Laid on a floor base of concrete and encased with the appropriate insulator/grout/sealer, then over laid with ordinary thickness ceramic tiles. This contractor has never had a failure like this before. I and my Electrician colleagues cannot understand why it will not heat up as compared to other identical installations which reach a nice 27C.+ within the hour and operate on a time clock. The current draw is 2.1A at 230V. ac. I have tried out a 30V. 'Boost' giving a 2.6A draw. Which resulted in only a 1C. rise over an hour, so as most of you have suggested, I think it looks like a base board heater to supplement unless anyone else can see a way around this I certainly do not want to tear it all up and replace, all though the contractor has agreed to do so. For the sake of a trial I am borrowing a 55V. transformer just to see what will happen although as several of you have said 500W = 500 W !
Trumpy , you can see how I do the voltage boost, see "Buck/Boost/choke test drawings" by 'Scott35' in the technical area.

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