electronic thermostats and baseboard crackle

[montreal]

Hi everyone,

I was so surprised to watch the hydro meter disk spin quickly for 10 seconds then pause for 5 seconds then repeat the same routine indefinitely. I wondered what appliance in the house was cycling at that rate. Eventually I came across the only electronic thermostat in the house and when I listened to the baseboard heater, I could hear it crackling every 15 seconds.

In other words, the electronic thermostat was providing full power to the heater for 10 seconds and then shutting down for 5 seconds. Each cycle caused the heating element to expand and retract, thus creating the crackling sound as the metal element slid forward then backward on its supporting suspension.

What a shame as I thought thermostat manufacturers would be using zero-crossing triac technology and duty cycles framed within the 60 hz. line frequency, just like an incandesent light dimmer.

But no, it seems many manufacturers have opted for the 15 second duty cycle instead of the 1/120 second duty cycle. The result is noisy baseboard heaters, a problem that electronic thermostats resolved over a decade ago when the first generation of electronics were indeed very fast acting.

Now we are ready to buy two more thermostats for the home and it seems none are on the market that have duty cycle calculated in milli-seconds rather than whole seconds.

Anyone aware of any obscure brand names that are fast switching?

Thanks

[ssbtech]

I too wouldn't mind knowing what might be available.

I have a couple of Honeywell thermostats that cycle the heaters on and off. The bedroom heater frequently wakes me up with the expansion/contraction as it heats and cools.

I can't imagine it being good for the heater, either.

[montreal]

With mechanical thermostats, the heater was cycled on once every 15 minutes or so. With many electronic thermostats, this happens every 15 seconds, in other words, the heater gets turned on 60 times more often per day. Now it is true that the heater is only off for 5 seconds at a time so the element never fully cools down, but there is still minimal expansion and contraction going on and that at 60 times more often, so there is more frequent rubbing of the mechanical parts at the points of contact.

Perhaps the only advantage of the electronic thermostat over the mechanical one is the moment of switching on and off the current occurs when the voltage is crossing zero, so you have less surging on the line and that means your other sensitive electronic appliances in your house see fewer transients.

[timlocke]

For pure resistance devices such as these baseboard heaters what is wrong with a good old fashioned mechanical thermostat. Bi metal strip or even, dare I say it, a mercury switch? Is it really necessary to switch crude things like baseboard heaters on and off every few seconds..or even milliseconds?

I have just had some baseboard heater installed in my basement, haven't used them yet but having seen these posts I will go and check the thermostats and if necessary replace them.

[ScaryBob]

Rapid switching increases the comfort level. Long heating cycles on conventional thermostats cause a heating/cooling cycle that results in drafts and discomfort for some people. Short cycle thermostats reduces this and probably save energy as well since they feel more comfortable at lower temperatures. While I agree that using a triac to regulate the heater would be ideal, I expect that it would raise costs considerably due to the high currents involved.

[montreal]

Using a triac instead of a contact switch in series with a resistive element heater in no way changes the energy consumption as recorded by the hydro meter. The peak current in the circuit is completely dependant on the heating element and not the switching device.

The only caveat is that with a mechanical switching device, in theory, the voltage drop across the switch is zero, but with a triac or any like transistor, it is between 0.5 and 1.5 volts. This multiplied by the current of the circuit, typically between 5 and 15 amps, results in the electronic thermostat generating internally between 5 and 15 watts. But this heat is minimal compared to the thousand watt heating element, and the waste is generally dispersed in the same room.

Another advantage of the triac when used in a 15 second duty cycle (which I detest) is that there is less EMF radiation and power line transients generated as the power switching takes place at zero voltage crossing.

On the other hand, in the old days when heater triacs were switched on in mid cycle like light dimmers, there would have been much more voltage spiking generated requiring expensive line filtering and suppression given the much higher currents in heating circuits compared to lighting circuits handling a few hundred watts.

[ssbtech]

If a dimmer switch for a light reduces the energy consumption, why wouldn't a "dimmer" switch for a heater do the same?

[das75]

Seems like a good thing. Heater is still radiating latent heat during the 5 seconds off.

[montreal]

Dimmer switches for lights are horrible inventions for saving energy. Indeed they actually cost more to operate per lumen of light delivered than going with a smaller wattage light bulb but with no dimmer.

Firstly, incandescent bulbs deliver a fraction of the energy they consume in light, most of the energy is lost in heat, which is not necessarily a bad thing in winter as the waste gets recycled into heating your house. In summer, it is however a real loss, twice over because you now have to run an AC to pump the light bulb heat outdoors.

Incandescent lights only begin to shine after their filament has been heated to a minimum temperature, usually meaning that 60% of the bulbs energy requirement must be spent before any light will begin to come out of it.

So your dimmer ends up operating the bulb in the upper 40% of the bulb's consumption range. Meaning a 100 watt bulb barely turns on at 60 watts and reaches full brilliance at 100 watts. So if you use a dimmer to put 70 watts into that 100 watt bulb, it will only put out 25% of its potential brilliance (((70%-60%/(100%-60%)=25%).

A 25 watt bulb without a dimmer would put out the same amount of light as a 100 watt bulb with the dimmer set at the point where 70 watts is going into the circuit. Better to consume 25 watts than 70 watts for the same amount of light. Sometimes you need a wasteful dimmer for mood lighting, which is OK in winter, as there is no money down the drain.

As far as the resistive heater goes, it is not like a light bulb. Every watt you put into the heater, you get back 100% of it in heat. If you put a 10000 watt heater on an electronic dimmer set for a 25% duty cycle, you get exactly the 2500 watt equivalent of heat in BTUs and you get charged by Hydro for this same amount.

My original post concerns my friends problem with her electronic thermostat and baseboard crackling (vibration).

In my house, I have designed my own electronic "dimmer" to control the two 5000 watt resistive elements in my central electric furnace.

Unlike with commercial electronic baseboard thermostats, I get around the problem of crackling by using a custom duty cycle of 1-2 seconds instead of 15 seconds. In other words my elements are never off for more than a fraction of a second at a time so they don't have a chance to contract. They just operate at a constant temperature that varies slightly as the outdoor temperature changes during the course of a day.

I also avoid the problem of EMF radiation and transients as my Solid State Relay circuit only switches at zero crossing of the line voltage. I have the best of both worlds - heater element silence and clean power in the rest of the house.

[montreal]

My friend finally chose a 5 pack of Honeywell baseboard thermostats which use the 15 second cycle time.

Just before doing so, I spoke with their telephone rep who recommended two tricks for reducing or eliminating crackle. Crackle may be caused by the heating element sliding unevenly on its fixed suspension points or a buzz sound due to an electromagnetic vibration from within the heater element core.

The rep suggested slightly loosening any screws that bind the element to the fixed suspension so that the element glides more smoothly at it contact point(s). The other suggestion was to coat the suspension point with automobile spark-plug anti-seize compound which supports high temperature.

As it turns out, we have not noticed any crackle with the baseboard heaters connected to our new thermostats located in the upper two floors.

We only have crackle in the one heater located in the basement which uses an Aube thermostat and for that one I will be applying the suggested remedies.

Thanks for all those who commented in this thread.

[gseamen]

Hi folks, I have 2 Honeywell and 1 Aube tstat installed. Both brands appear to be the same except the Aube has a handy light. These have been in place for a couple of years. Originally I had them installed without the FAN option enabled. They baseboards seemed to stay on much longer than they do now in FAN mode.

No crackle from them though.

Should I be leaving FAN mode off for better efficiency? This thread has given me food for thought.

Thanks

Greg

[montreal]

The thermostats we purchased also have the option to configure for a fan. The manual says that in fan mode, the cycle time is 5 minutes instead of 15 seconds.

I am unhappy with 15 seconds as I can hear the baseboard heater located 25 feet away in my friend's guest bedroom generating a crackling noise while I'm trying to fall asleep. Fortunately the tstat in her master bedroom is turned off for the moment.

If you have a fan assisted heater, then I think it would be unwise to switch to the 15 second cycle mode as there is the risk of the fan circuit burning out prematurely from cycling on and off too often.

I am pleased to discover the existence of a 5 minute fan mode as my choosing this will allow me to reduce the frequency of crackling.

I can't imagine any downside to choosing the fan mode in an installation that has no fan. These thermostats will do a good job of economically regulating the room temperature regardless of cycle time.

[gseamen]

Thanks Montreal, I have some 20 + year old heaters in the bedroom connected to old bi-metal tstats they are REALLY noisy at times. I am going to replace them with some newer Dimplex ones once I do some research.

Greg

[montreal]

Good luck Greg with your baseboard purchase. I don't know which brands generate the least mechanical noise.

I thank you for bringing to my attention the fact that the fan cycle is much longer than the non-fan cycle.

[airmike]

I spoke to a manufacturer in Quebec last year and they recommended the pulsating electronic thermostats over the ones that continually provide power without pulsating for baseboard heaters. I'm not sure if all electronic thermostats do this, but Stelpro and Oulette offer pulsating ones - Stelpro electronic pulsating thermostats are made in Quebec and Oulette are made in China. I actually prefer the pulsating ones since the heaters don't heat to extreme temperatures and cause burn looking marks on the wall. Also, i don't get extreme cracking noises that I got prior to putting in the pulsating thermostats. I'm very happy with the pulsating thermostats!