How to raise efficiency of furnace?

[oil pan 4]

You could always put a stack robber on there.

[Isaac Zackary]

Originally Posted by oil pan 4

You could always put a stack robber on there.

There's probably a way to do that. Although the 6ft high furnace in the wall of a 7ft high trailer house doesn't give me much room to work with.

[Isaac Zackary]

And the results are in, and they are.

......Drum Roll!!........

A 100% improvement!

So I did a test this morning. Normally I'll go warm the house up from 40*F to 50*F. This has been taking approximately 1 whole hour, maybe even a bit longer. The outside temperature has been around 0*F, the same today so no variables have changed.

Well today I turned up the thermostat I took the cover off and then momentarily turned off the power (no need to get shocked) and took the spade connector off that goes from the thermo switch to the fan and hooked it directly to an empty terminal on the power block so that the fan would stay on. 30 minutes later the thermometer read 50*F!

So with the fan turning on and off it takes 60 minutes to raise the temperature 10 degrees. But with the fan on permanently it only takes 30 minutes! So I just used half the fuel to do the same thing!

[Isaac Zackary]

Ok. So I found the specs on my fan switch. It's a 110*F fan switch:

OEM Coleman Evcon Furnace 110 F110-20F Disc Fan Switch 7660-328 7660-3281 4066-3281 - North America Distribution-Sellersburg Heating

I tested it in a plastic bag in water. It seems to come on and off right around 110F.

I went ahead and ordered an adjustable one with a lower limit of 70*F/90*F off/on to a high limit of 110*F/130*F off/on. I'll let you know how it goes.

[freebeard]

Bang-bang control?

On Youtube AvE replaced a one-phase air compressor motor with a polyphase motor/controller and gained 40% throughput. It's a compressor rather than a ducted fan, but maybe something similar?

[oil pan 4]

The fan was cycling on and off?
Something is very wrong.

[Isaac Zackary]

Originally Posted by oil pan 4

The fan was cycling on and off?
Something is very wrong.

It only cycles on and off when I'm trying to heat the house to a low temperature like 40*F. When it's above 60*F it's fine and doesn't cycle on and off. I also conducted some similar tests at temperatures between 50 and 60*F and didn't notice as much of an improvement in efficiency like I did at 40 to 50*F. Between 60 and 70*F the furnace just stays on without any cycling so there's no difference in efficiency by hardwiring the blower on during that time.

My take on it is that the furnace is designed to run efficiently at around 70*F. The idea being that if the air going into the furnace is 70* it will have heated up to 110* by the time it reaches the switch. But if it's 40* it will not have heated to 110* and so turns off the switch. For it to work the same the temperature difference should be the same because the air is only going to increase by about 40* or so by the time it reaches the thermoswitch.

Basically this:

House/Thermoswitch
40*/80*
50*/90*
60*/100*
70*/110*
80/120*
90/130*

So if the house is at 40* the thermoswitch should be at 80* because the air will only heat up 40* more than 40* by the time it reaches the thermoswitch.

[oil pan 4]

I have worked on portable diesel fueled heaters that would run open loop with 0°F air going into them and the discharge air would still hit nearly 200°F.
They were basically a fuel oil furnace on wheels with removable ducts and a low, medium and high heat setting.

[roosterk0031]

The 60,000 btu Rudd 1977 that I have in my non-insulated garage used to do the same thing. If the heat exchanger gets too cool it turned the blower off. Never turned it on unless below freezing. Never did it when it was installed in the house.

[freebeard]

Hey, I have a Rudd water heater; like this one


ANTIQUE RUDD NO.25 CAST IRON EMBOSSED WATER HEATER SURROUND,STEAMPUNK,BLACKSMITH - Augusta, ME - $390

Apparently it's worth ~$390. "IN GREAT SHAPENO COPPER COILTHE" No wait, more. That's a great sales technique with the sparse punctuation.