How to determine proper on and off blower delay?


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Old 11-25-10, 11:45 PM
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How to determine proper on and off blower delay?

Control board had been replaced by previous homeowner, they set the on-delay to 30 seconds and the off-delay to 140 seconds... the off-delay seems excessive, but couldn't determine any way to properly set this. I'm questioning this because I already found they had hooked the blower up to the wrong speed for A/C (schematic states black wire / hi for AC, was set to medium) so it makes me wonder what else they didn't properly configure.

The unit is a 3 burner 75,000btu 80% heil/arcoaire.
 
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Old 11-26-10, 07:45 AM
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Most are fixed on 30 sec.

As for off, some time longer is better, it give a chance to cool down the heat exchanger and left over heat into the house.

As for the blower speed for A/C, it may been dropped to match the CFM for the A/C size. Rule of thumb is 400cfm per ton. I've changed blower speed all the time to match the A/C, "Black/high" is not always better on the comfort side.
 
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Old 11-26-10, 08:29 AM
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I reduced the off-delay from 140sec to 100sec as I found the manual online and it didn't specify a default, 140 blows cold air
 
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Old 11-26-10, 03:05 PM
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Then drop it down to 100. That what most of them are.

Figured out your A/C blower speed?
 
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Old 11-26-10, 06:43 PM
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Yeah, as the schematic specifies black should be connected to cooling, which I did for the summer and saw a 18-20f t-delta and good comfort.

Currently i'm running the honeywell with a CPH of 3 and the proper speed setting, problem is the thermostat calls for and then cancels heat quickly... usually under 3 minutes with an outside ambient temp of 25f.

The house is a 1000sq/ft foundation 100% finished split level (2000 total livable sq/ft) with 18" of cellulose and is 9yrs old, furnace has it's own fresh-air supply from outside as well as another fresh-air combustion supply, furnace room is enclosed.

Is this an issue of oversize? It's irritating to continue to short cycle, not run the blower for 30 secs on start, run for 3-4 minutes, then run blower for 100sec for it to turn back on and do it again 10-15 minutes later.

If I ever replace it I think much smaller than 75,000btu would do the job.
 
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Old 11-26-10, 08:14 PM
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Ac speed could be set lower for longer run times and more rh removal
 
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Old 11-26-10, 10:09 PM
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Originally Posted by airman.1994
Ac speed could be set lower for longer run times and more rh removal
The AC seems to be tolerable, although it is probably oversized too (2.5ton), my compliant is the short cycling during heating.

A friend of mine purchased a home by the same builder and while the foundation size / layout are the same, only a quarter of the basement is finished and they used a 50,000 btu 80% there... that's what made me think this one's oversized as 50k btu does fine for him throughout the whole house.
 
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Old 11-26-10, 10:57 PM
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Why not turn the fan on! This will help with hot and cold spots. It will also keep the home at a more even temp which could help with the short cycling.
 
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Old 11-26-10, 11:31 PM
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Originally Posted by airman.1994
Why not turn the fan on! This will help with hot and cold spots. It will also keep the home at a more even temp which could help with the short cycling.
The temperature is static throughout the upper level, i've checked.
 
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Old 11-27-10, 04:14 AM
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You could drop the CPH down to 2, and that may help. Also, make sure the t-stat is not getting a false reading from a nearby vent.
 
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Old 11-27-10, 01:10 PM
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Originally Posted by Jay11J
You could drop the CPH down to 2, and that may help. Also, make sure the t-stat is not getting a false reading from a nearby vent.
Temperature is uniform across the entire upper level (where the tstat is in the center, on an interior wall and I even sealed the wire opening)

It's just a really tight house so the temperature rise is quick, would it make any sense to lower the fan speed further if temp rise is still ok or would that just equate to longer runtimes and similar cycling resulting in more natgas usage?
 
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Old 11-27-10, 04:17 PM
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Fan speed could be slowed down, but do a temp rise check to be sure it's with in the specs of the manual.

You may save on the gas since it's a longer run time.. Longer run time some times use less gas than the stop and go.
 
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Old 11-28-10, 09:35 PM
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Is there any benefit to replacing the unit with a properly sized 95+% efficient system? I would like greater control upper/lower level and more effective use of natrual gas.

Lately it has been 20-32f ambient temp and with a CPH of 3 and the stat set @ 69f continously i'm burning 3ccf per day, .5 of that is the water heater so that equates to 2.5 CCF of usage per day for the furnace @ 75,000 input, or 8 minutes 30 seconds per hour.

Comfort is good, no drafts or necessity for calling of heat noticed, since I plan to sell the home next year and upgrade maybe it makes no sense to change anything? Still even with this light amount of usage... 90ccf's still equates to ~$100 a month for natgas which I don't like.
 
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Old 11-29-10, 04:51 AM
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My last month gas was 29 ccf, (I have gas stove, dryer, furnace, and water heater. We even had company for 3 days.) and that breaks it down to 1.02 ccf a day.

An over sized furnace is going to use more gas too.

If you get your new 95% furnace and A/C before end of the year, you can get tax credit.

Have you done a Manual-J to see what your home calls for sizing?
 
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Old 11-29-10, 06:14 AM
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I haven't done a j-load myself because I don't know what sidewall insulation or exact thermals of the windows, I just know the furnace seldom runs and houses with a similar foundation use a smaller unit and have less attic insulation.

I used 35ccf last period w/ gas drier, stove, water heater and furnace... but it's been wet/dark/cold since that billing period and i've used 38 since nov 9 (was home a lot over thanksgiving break which isn't normal)
 
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Old 11-29-10, 08:35 AM
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How long have you been in the home? If you had last winter, on the cold snap, did the furnace run steady?
 
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Old 11-29-10, 08:47 AM
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at 0f at night it would run a good bit, but nowhere near steady.

I explained the housing details with a HVAC contractor and he said he's done enough J-loads on similar houses to say a 60,000btu would do it and recommends a carrier 95% 2-stage... however we're looking at around $3200 to install that, doesn't seem to be too cost effective since i'm selling in the not so distant future :/ what do you guys think?
 

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Old 11-29-10, 02:35 PM
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If you are selling soon, then let it be. You are not going to add any value to the home with this change out if you do it.
 
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Old 11-29-10, 02:50 PM
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Originally Posted by Jay11J
If you are selling soon, then let it be. You are not going to add any value to the home with this change out if you do it.
Now knowing much more about home efficiency, if I buy a house built 2008+ am I guaranteed it would pass an energy audit with flying colors? Is there any way to seek out "certified" homes? Seems with the cost of energy every new house should be energy audited? I'd easily pay $250 or something to know what i'm buying needs no energy improvements.
 
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Old 12-20-10, 01:02 AM
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Hey Guys (& Gals?)
I'm new at this, using forums, so bear with me. I know a little about furnaces (oil and gas) having been a homeowner a number of years, but some of the terms you guys are using I do not know like "CPH", "J-load". I could probably find them in Wiki-, but enlighten me, though this is not the purpose for my writing.

My Problem: I am staying temporarily at a friend's house while he is away, and his furnace is cycling quite often. Runs (blower on) for 7 minutes, off for 4-5 then back on for about 7 minutes which the math shows this thing is running 5 times an hour. Temp outside is in the teens to 20s at night, a tad warmer in the day (Kalamazoo, Michigan). It doesn't matter what I set the t-stat to it does this, and I have no idea how much money is going out the chimney. I have changed the furnace filters as suggested (and which it needed) on more than one website, which I was sure wouldn't help. The t-stat is a Honeywell CT87N (which I have read some not-so-nice things about...), and electronic, so I am not able to adjust a heat anticipator, at least I have not found one on the unit. I also cannot find a manual for the thing. the temp doesn't have a chance to drop because the furnace cycles so much.

Years ago I had a similar problem (somewhat) with my own furnace, except my furnace wouldn't run very long--a couple of minutes tops- turned out to be a spider and it's food (a cocoon) blocking the orifice of the burner (or gas valve). The firebox wasn't getting enough flame to maintain the heat and was shutting down the system, only to restart a minute or so later. It happened this year also just before we entered the Deep Freeze. So I checked this on my friend's furnace just to make sure, but it was clear. One of the things I remembered from my own furnace problem was the orange flame, which was supposed to be mostly blue, I believe. My friend's flame was a little orange, but all the pathways for the gas/air mix are clear.

I think the t-stat is faulty. What do you think, Jay, (anybody else)?
 
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Old 12-20-10, 01:11 AM
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BTW I once saw a bumper sticker that read: "I'm not the King of My Castle, Just The Mechanic", and so when asked what I wanted for a user name on this site, it seemed perfect, and no one was already using it.
 
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Old 12-20-10, 04:53 AM
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Sounds like the stat is left a the default mode. Looks like Honeywell's web site is down right now, so I am not able to pull the page up on this.

On the back of the stat itself, there should be a couple of dipswitches, and not sure if this is printed on there or not. but set it to 3 CPH or "high eff/Hot water".

"CPH"- Cycles per Hour. THis is Honeywell's way of controlling temp at 50% load. IF the load is in higher demand, it will lead to longer run time. If the load is light, then it will run less The stat "looks ahead" to advoid the temp change. That's why you are not seeing the up and down on temp that you'd see on some other brands.


"J-load"- Manual-J. Is a program that a dealer use (not many do) to find the heat lost/gain on the home to get the right size equipment.
 
 

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