Thermostat accuracy

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Old 01-18-05, 06:03 PM
K
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Thermostat accuracy

Hi - i thought this might be electrical question - but didn't see thermostat in any topic

My question:

Tenant called complaining heat wasn't working properly that thermostat set on 70 inside temp 63 (its below zero right now and a plank house I installed insulation where accessable, but I'd say the insulation is minimal). The furnace would run for a while then stop even though temp wasn't hitting 70.

Plumber suggested changing thermostat as it was a programmable one and tenant continually "played" with it. (Tenants girlfriend verified this)

Had thermostat changed, system checked (baseboard) everything ok.

Called tenant who said "Well it was working ok, but now set on 70 and its only 68 in here". I explained that plumber said thermostat only accurate w/in 3-4 degrees (one of those old dial types) and suggested he put heat where comfortable rather then watching the thermostat. He insisted that at the last place he lived the room temp & setting were always the same.

Should room temp read 70 if it set on 70? Or is plumber correct in saying there may be a 3 - 4 degree difference?
 
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Old 01-18-05, 06:45 PM
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You said 'old' dial type. If he put on an old thermostat, anything goes. If he put on a new one, it will be acurate to within 1 degree if it is installed properly and the anticipator is set right. 3-4 degrees is a little extreme. The other thermostat was probably accurate but it probably had a cycle rate control built in so it could not run the system 100% of the time. That's where you begin to lose temp on very cold days.

Ken
 
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Old 01-18-05, 07:13 PM
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thermostat accuracy

It was old style (compared to programmable) not an old (used) thermostat.

So can the cycle rate be changed? and if so would having it run constantly be a good idea?

Would setting it higher help or will it still continue to lose heat?

Is there a "fix" for this?

Don't mean to sound so ignorant - I don't think I've ever studied my thermostat - if its cold in house I turn it up & if its warm I turn it down I have no idea whether there are a few degrees difference between setting & room temp... but 64 is comfortable in this (leaky terribly insulated house) so maybe my thermostat is shot too!
 
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Old 01-18-05, 08:29 PM
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If the sub-base of the thermostat is perfectly level, it will be accurate. A mercury thermostat needs to be level or it is worthless. Not almost level, but perfectly level. If it is adjusted by comfort using the lower thermometer for reference, it doesn't really matter what the upper dial says. If it is always off by 3 or 4 degrees and it doesn't bother the user, so be it. It will still hold the temperature at the setpoint, it just won't display the setpoint properly.

Ken
 
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