Heater Controls

[bthielen]

This is not a code question but a design question I'm hoping someone can offer a possible solution.

As part of my home remodeling project, I had installed electric baseboard heaters throughout my home as part of a dual-fuel heating system. My goal was that the electric heating system would be my main system and my fuel-oil system would serve as a backup. Right now, because of the dual-fuel price incentives, it costs about 1/2 as much to use electric heat over my fuel-oil system.

The first heater I put in seemed to work just fine using heater mounted thermostats so I figured I would do this for all rooms rather than using wall mounted thermostats. This made wiring much easier and saved a few bucks, too. After all, this was a DIY project you know. These thermostats are nothing high-tech, just bi-metallic and there is no temperature setpoint reading or display.

Here?s the problem I have been having. I have the thermostats marked so I know where to set them to maintain about 68? F. in the room under most conditions. For some reason, I have found that the colder it gets outside the higher I need to set the thermostats on the heaters in order to maintain my desired setpoint. For example, this year has been unusually mild with the outside temperature consistently ranging from morning lows in the lower teens to highs in the mid-twenties.

This morning I awoke to -21? F. outside and my fuel-oil furnace was running. I have the thermostat for the oil furnace set at 65? F. as a backup. The electric heaters were not putting out heat so they didn?t believe the room was cold.

Some of these heaters and their thermostats are located on outside walls below windows (usually preferred) and some are not. I would expect those on outside walls to be more likely fooled into believing the house was colder than it really was, not the other way around.

I don?t seem to have any problem with temperature swing in the room once the outside temperature stabilizes so the thermostat hysteresis doesn?t seem to be a problem.

The only explanation I can come up with is that because the thermostats are mounted on the baseboard heaters, the heat radiating from the heater itself is interfering with the thermostats ability to sense actual room temperature and therefore is fooled into believing the room is warmer than it really is.

These heaters do have over-temperature sensors to protect against overheating but that does not appear to be the cause. All I have to do is turn up the thermostat and the heaters function fine so the sensors are not preventing the heaters from working.

Any other thoughts?

Thanks, Bob

 

[charlie b]

Re: Heater Controls

Originally posted by bthielen:. . . the heat radiating from the heater itself is interfering with the thermostats ability to sense actual room temperature. . . .

That explanation is so likely to be the correct one that I am surprised the manufacturer even offers the option of mounting the thermostat on the heater itself. I think it cannot hope to function as desired in anything other than a small room. Do you have the option of moving the thermostat to another location, the temperature of which is more likely to be representative of the average temperature of the room?

My other question is whether these heaters include fans. I have baseboard heaters in my dining room, and they are the only heaters in the house that do not have fans. They are also the only ones that fail miserably to add sensible heat to the room. I suspect that a model that blows hot air away from the heater is less likely to interfere with the ability of a heater-mounted thermostat to correctly assess the temperature of the room.

 

[bthielen]

Re: Heater Controls

As you suspect, these heaters do not include fans. As far as relocating the thermostats, that may not be entirely out of the question but won't be a simple project either. I would probably hire an electrician simply because he/she would more likely have the tools and expertise necessary to simplify the project and do it with minimal impact.

Thanks,

Bob

 

[LarryFine]

Re: Heater Controls

It's important to understand that a thermostat can only maintain a given temperature where the thermostat is located, like a hallway. That's why I always recommend setting a forced-air system's fan switch to "on" instead of "auto".

Keeping the fan running also reduces temperature swings in rooms away from the thermostat, especially those spaces with large windows and other high-heat-loss characteristics, such as a large exterior surface area.

A heating system replaces heat loss from the living space. It's natural that a colder outside temperature requires the heater to be warmer where it is located in order to keep the other side of the room at a given temperature.

You might look into methods of reducing heat loss as well as increasing heat production. Your money will earn a higher rate of return. Meanwhile, relocate the thermostats to the wall(s) opposite the heater(s) for better regulation.

 

[tshea]

Re: Heater Controls

Install low voltage t-stats wired to relays to turn on the bb. Sparky will need to install control xfmr. Grainger makes a real nice unit called level control. It has a built in xfmr. I have used in the past and can not complain.
Fishing 18-2 tstat wire is easy compared to cutting in boxes for line voltage t-stats.

level control