|
Posted by Zyp on February 17, 2008, 5:26 pm
becauseofjunk@mailcan.com wrote:
> On Feb 16, 7:53 pm, becauseofj...@mailcan.com wrote:
>> I'm sorry, I thought the tread was about the flame roll out not the
>> blocked flue switch. Can you clarify????
>
> First, I'm concerned the furnace is oversized for application which
> would cause short cycling, moisture in heat exchanger, rusting of
> burner and sooting of cells.
>
> Have you had a Manual J, Heat/Load Loss Calc done on 1st floor? If
> not, I highly recommend it. Any reputable contractor will do this
> during their estimate on a new furnace, it is becoming law in a many
> states.
>
> You could easily tell if your furnace is short cycling by watching it
> when you turn your heat up high, say 10 degress. Watch the flames, do
> they shut down and blower continue to run with the thermostat
> unsatisfied? If so, your furnace is short cycle, overheating. After
> enough time, this can cause moisture to build up in the heat exchanger
> just like only taking short trips in the car to the grocery store can
> rust out your car's exhaust system.
>
> For a roll out switch to trip, it happens for couple of reasons. What
> I am hearing is that instead of rollout switch being licked by flames
> rolling out of combustion chambers, the heat exchanger is overheating,
> transferring heat into the front plate and then into the bracket that
> holds the rollout switch then tripping the switch. (Unrelated: Rheem
> had a problem on particular furance where there was a Service Alert to
> replace the bracket on their rollout switches for this problem--not a
> Rheem dealer, but you techs know--we service all makes and models).
>
> Another way to tell if enough air is getting past heat exchanger is by
> doing a CFM test. By this you measure the return air temperature and
> supply air temperature (supply temp minus return temp). This is
> called deltaT (temp differential). Take bonnet BTU of furnace (not
> input but output, for example: input BTU, 125k btu furance multiplied
> by efficency, say 65% or .65) divided by deltaT that has been
> multiplied by 1.08. CFM for 125k BTU, I'm hoping you have 1600 or
> better for your furnace.
>
> bonnet BTU
> CFM = _____________________
> deltaT x 1.08
>
> If not moving not enough air, get the Manual J. If furnace is sized
> properly for house, then insist on Manual D...and always change your
> filter. (may I suggest you avoid the pleated filters at this stage??)
Wow, such detail for such a interesting quandary. Are you sure of all that?
Perhaps you want to just camp at his house for the afternoon.
Could be something as simple as leaving the blower door on the furnace ajar.
Combustion air vent [inlet] blockage for the equipment closet? Could be
something as simple as a failed firebox. Doubt it's the switch. Doubt the
firebox is seeing to much heat [transferring it to the switch]. If the
firebox was sooting, and, there was flame impingement, it can have a
rupture. A rupture that doesn't show on visual. It could open after
heating a bit causing flames to roll out. [There's a reason the Mfg. put
the switch in the first place.]
--
Zyp
| 
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap