# Question on home heating furnace



## Flyinfool (Dec 24, 2020)

My furnace always seems to run fairly short cycles. These short cycles are being commanded by the thermostat.

My question is, How short is short?

As is a typical cycle lasts about a minute from the time the Furnace blower kicks in to the time the thermostat is satisfied and ends the call for heat. It will then be just 1 to 10 minutes depending on outside weather till this repeats. I would think it would be more efficient to have the furnace run fewer longer cycles.
In the setback mode, I have it set back 10°F at night, It only takes about 10 minutes to have the house back up to temp at the end of the setback.
Does mean my thermostat is to sensitive?
Or maybe is my furnace to big for the house?

I have looked inside of the thermostat for any kind of anticipateor type of setting, there are no internal adjustments of any kind I can find as seems to be the case with most electronic units.


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## mmcmdl (Dec 24, 2020)

I had this problem also , oversized furnace .


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## Flyinfool (Dec 24, 2020)

At the time I got this one it was 10 below zero and kind of had to take what they had in stock.

What is the best way to determine what size I should have?


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## mmcmdl (Dec 24, 2020)

I don't have that answer but I know they have calculations . 

What happened to me ......................

I bought a house 2 houses up from my original house and shop back in 93 . The house was approx 2300 SF . The furnace was only heating half of this house and short cycling like yours . I asked my co-worker what was going on and he said my furnace was larger than his and he heated a 3500 SF space . 

What I ended up doing was ripping all duct work out of the basement to the upstairs , and added ducts to the other side of the house . We generally don't use the electric baseboard heaters any more because the furnace can breathe better and spread the heat thruout most of the house now .


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## Alexander McGilton (Dec 24, 2020)

I think the hysteresis of the thermostat is too low, or it is placed too close to an adjacent vent. Too many on/off cycles can shorten the life of your furnace motor and any moving parts of the gas regulator or electrical contacts.


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## mickri (Dec 24, 2020)

On my thermostat you can set a temperature range to turn the furnace off and on.  For example if the thermostat is set for a 1 degree range and is set for 70* The furnace will turn on at 69* and turn off at 71*. This is a pretty typical factory setting.  If set for a 2* range it turns on at 68* and off at 72*.  Where the thermostat is placed is another factor.  My thermostat is place 4' off the floor and close to the return air vent.  No heat vents are close.  So the thermostat is governed by the temp of the air getting sucked into the furnace.


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## talvare (Dec 24, 2020)

It's possible that it is not the thermostat that is causing the short-cycling. Other safety devices like the thermal cut-out switch or the fan proof switch could be defective. May pay to have an HVAC tech troubleshoot it for you.
Ted


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## pdentrem (Dec 24, 2020)

How modern is the furnace? Could be the thermostat as mentioned.
If a hi efficiency with sealed air system. 
Check for a trouble code light that will blink the number. Usually have to open the access panel. The codes are typically printed on the panel or near by.
Check for blockage on the air supply pipe and exit pipe. There are sensors on each. Also check the water trap that is under the condenser that is before it drops to the drain line. They do get plugged with debris and need to be emptied every couple years. Have a bucket ready to catch the water if so. 
Pierre


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## RJSakowski (Dec 24, 2020)

Thermostats have different setting for the type of heat that you have.  Depending in the thermostat, the adjustment varies.  A shorter cycle rate will provide more uniform temperature control at the expense of more wear and tear on the equipment and lower operating efficiency.  My Sensi thermostat has three settings; fast, medium, and slow.  My old programmable Honeywell had a two position switch for fuel or electric heat.  I believe the still older round Honeywell thermostats had a mechanical adjustment.


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## Flyinfool (Dec 24, 2020)

It is defiantly the thermostat.  I can hear the relay open and close that commands heat on and off, and the furnace is following that exactly. 

I found an online calculator for furnace sizing Using the worst case load factor I should have a 48,000 BTU, I have an 80,000 BTU in a house that is 1,100 square feet.

I wonder if that is part of my problem too.
I have  3 of the 4 bedrooms with the heat shut off cuz I don't use them for anything other than storage. That means I have 80K BTU feeding about 2/3rd of the house.I wonder if it might be more efficient to open those rooms back up to have better use of the furnace.

The cold air return is directly under a picture window, that would be a bad place for the stat.The heat vent in the room is nowhere near the stat nor is it blowing toward the stat. the stat is very close to centered in the house, on an inside wall that does not go to the attic.

The drain was just replaced last year and now has a sensor to warn me if water is backing up.
It is not quite new enough to have trouble codes. Just a bunch of relays.

It is sounding like my furnace is just to big.

This old gas furnace is only 38 years old and was a high tech at 92% efficient, great for the day.

I had been looking at replacing it in the not to distant future, but every time it stops working I have been able to find parts to fix the problem. 
Since my house was built in the late 1800s, still has the original single pane windows, and only as much insulation as I could sneek into the walls, I am thinking of a 60K BTU for next time.


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## pdentrem (Dec 24, 2020)

Sizing is approximately the same as AC, 12000 btu for every 500 sf. My house is 1900 sf and furnace is 40K btu on 2 burners.
Pierre


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## RJSakowski (Dec 24, 2020)

My adjustment for the Sensi thermostat is in firmware, programmable through a smart phone app.  The Honeywell adjustment is on the rear of the thermostat, only accessible by removing the thermostat. Once temperature is reached, our  L.P. furnace will probably run for around five minutes in each cycle.  The off time depends upon the outside temperature.


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## mksj (Dec 24, 2020)

I would suggest you look into a different "smart" thermostat that is more adjustable. You can set the temperature swing  (heat differential setting) to decrease the on/off cycling as well as time (heat dissipation time) when the furnace shuts off after the burners turn off. If you had a variable speed furnace you could modulate the heat output and fan speed which saves energy and is more comfortable.  In addition some thermostats have a remote battery operated wireless sensor so it can be controlled by the temperature in a different location vs. the main thermostat. I have the Ecobee 4, they now have the 5 with native voice control. Does a very good job of modulation the temperature and they have a motion detectors so if it does not sense motion it can turn down the heat. It has a fairly elaborate menu system of adjustments that can be done on screen, smart phone or computer. I tried Google Alexa to control things, but she got banished from my house. There are often rebates for these smart thermostats that make them more reasonable. I do not use any of the learning modes, I prefer to set all my own controls, but if you leave the house the Ecobee will go into vacation mode with no movement or you can use your smart phone.  Well worth the investment. I recommend the Ecobee over the Nest, the latter I have had more people complain about the thermostat having a mind of its own.





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						Help Centre
					






					support.ecobee.com


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## machPete99 (Dec 25, 2020)

Older thermostats had a "heat anticipator". It was basically a way to appy some curent to the thermostat coil to heat it up, causing it to shut down the furnace before the room got up to full temperature, so it would not overshoot. Some of these are adjustable with a dial (rheostat). Newer electronic thermostats probably do something similar in firmware, check the settings.


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## talvare (Dec 25, 2020)

Flyinfool said:


> I have  3 of the 4 bedrooms with the heat shut off cuz I don't use them for anything other than storage. That means I have 80K BTU feeding about 2/3rd of the house.I wonder if it might be more efficient to open those rooms back up to have better use of the furnace.



Closing off too many registers can definitely cause your problem. As I said in my earlier post, the unit could be cycling on the high temperature thermal safety switch. If you cut down too much air flow over the heat exchanger it gets too hot and shuts the unit off. When the thermal switch cools down and re-closes the unit will re-start (unless the thermal switch is a manual re-set type). May be worth checking.

Ted


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## Flyinfool (Dec 25, 2020)

The more research I do into this the more screwed up I think the whole system is.

I set up a temp probe right next to the thermostat to see what the actual temps are doing.
The thermostat is trying to hold temp on this old house to within 1/2 degree. the stat asks for heat when the temp drops by 1/2° and shuts off when it reaches set temp a half degree higher, the room then climbs a half degree more while the furnace is in cool down mode. 
There are no adjustments of any kind on this stat, I even took it down to check the back.
I guess this means that I need a new stat.

It is not the furnace hitting over temp It is defiantly the stat that is doing it all, I have an indicator to tell me when the stat is asking for heat.

I was hoping to be able to do a new furnace next summer anyhow, it has to be a summer job cuz I want to move the furnace to a different location in my shop, more out of the way and with the rest of the appliances (washer, dryer, water heater, laundry tub). This means plumbing changes to make room and a lot of duct work and even some structural work on the house. but it will make a lot more room in the shop.


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## RJSakowski (Dec 25, 2020)

Our electric utility is Alliant Energy and every so often in partnership with a group called Focus on Energy, they send me offers for free or greatly reduced products related to energy saving.  Several years ago, they offered a choice of one of two free smart thermostats; one the Nest thermostat and the other the Sensi thermostat.  I chose the latter.

There may be similar programs with your utility company.  Worth checking out.


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## ddillman (Dec 25, 2020)

Mine did that at first then I found the thermostat was set for electric baseboard heat. changed it for a gas furnace and it fixed it


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## JPar (Dec 26, 2020)

We had a lot of trouble with short cycling when we moved into our current house.  It was more with the AC than with the heat.  I tried different things, including a fancy new thermostat that had an adjustable range between the "on" and "off" temperatures.  Nothing seemed to work.  Then, one day I was fiddling with it and I just happened to have the thermostat pulled away from the wall.  The AC came on, and I immediately felt a cool blast of air coming out of the hole in the wall for the thermostat wire.   With the system running, a pressure differential existed between the basement and the upstairs, causing cool basement air to enter the stud cavity and exit through the thermostat wire hole in the wall.  It caused premature cooling of the thermostat, which then shut the system off.  I plugged the hole with a little caulk, and after that everything worked fine!

Again, we had more trouble with AC than with heat, but it's possible you could have a similar problem.
John


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## Dabbler (Dec 26, 2020)

@Flyinfool give this a try:  turn your fan switch to have the fan continuously run.  I put in an 80K BTU 92% furnace inmy house years ago, and we don't have a  short cycle problem.  Our thermostat is located in the updtairs at the farthest point from all the vents, and we run the motor 124/7 365.  This makes the heat even in the entire house winter and summer...


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## Larry$ (Dec 26, 2020)

I think Alexander had it correct. Your old ducting is the reverse of what is now used, at least in this area. Warm air would be sent via floor diffusers at the outside walls and under windows. Return air would be high on an inside wall. This reduces the variation in room temperature as the furnace cycles. The poor thermal condition of your house also will cause rapid temperature changes leading to cycling. The hysteresis setting may be correct for a modern house but not one that loses heat so rapidly.  Unfortunately setting for a greater differential will result in greater swings that you will feel. Get some storm windows. See if you can seal up any air leaks. If you have a basement insulate the box joist spaces. Next spring put blue or pink foam against the basement walls down 3' into the ground and above grade cover it with some of the fabric/resin systems almost all the way up to the framing. If you are in a termite area use termite shielding, or an inspection gap, or treat the ground around the house so they can't go up between the foam & the masonry.  

If you do most of the work except termite treating you will probably recover the material cost in a few years fuel costs. AND your furnace will cycle less.


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## chip maker (Dec 26, 2020)

I have to agree with Dabbler, I have my fan running year round with the new smart thermostats there is a setting that you can set the fan speed as well. Mine setting puts the fan in a slower speed so you don't even know its running. I also noticed that in the summer if you have return vents in the basement open it will pull the cooler air out of the basement and help with the air system. Not only it also keeps the air in your house being curculated all the time.


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## pdentrem (Dec 26, 2020)

Since this appears to be a new problem after a number of years, likely it is a failure of the thermostat with maybe some environmental changes in the house.

I run a whole house HEPA filter off the furnace, at all times. It does help balance the hot and cold spots in the house.

As I have been adding insulation where I can the bills have been getting smaller. The most recent change was to use Dri-core panels on the basement floor. Once that cold concrete was covered, the temp in the basement came up to mid upper sixties from 60-61. Sweet!
Pierre


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## Tozguy (Dec 26, 2020)

Flyinfool said:


> Since my house was built in the late 1800s, still has the original single pane windows, and only as much insulation as I could sneek into the walls, I am thinking of a 60K BTU for next time.


Sounds like our house. Built in 1947 it had single pane windows and skimpy insulation by 'todays' standards. The house was originally heated by a monster coal furnace. The central ventilation fan was on full time. No chance for cycling with that set up cause there was no thermostat.
Over the years the insulation was upgraded and heating was switched to oil with a thermo pump added eventually. Upgraded insulation measures (triple pane windows, thicker walls, blown in insulation and sprayed on PU) were essential to slow heat loss to levels compatible with thermostat control.
I really don't see how to solve your short cycling problem without slowing the rate of heat loss to the outside.


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## 7milesup (Dec 26, 2020)

Short cycling is almost always caused by improper sizing of the equipment.  Couple that with an extraordinarily inefficient house and there will be a lot of issues.  A lot of people like the "charm" of old houses, but the mechanical side of them (plumbing, insulation, heating, cooling, air quality, electrical, windows, etc.) are usually a disaster.  I know that moving may not be an option, so the best you can do is to have properly sized equipment and utilize stop gap measures to minimize energy loss.
To analyze your system and develop a corrective plan would require some work.  If you want to contact me, I would be glad to help as much as possible.  I am not a HVAC contractor or specialist, but I have built two very energy efficient houses in the last 12 years and have studied energy efficiency  a fair amount.
My most recent house (last year) is 3400sq ft total, including the walk out lower level.  4-4.5" of closed cell foam in the walls.  All penetrations in the attic sealed with foam and 24" of blown cellulose.  Triple pane windows from --->Accurate Dorwin<--- which also have fiberglass frames that are foam filled to reduce thermal transfer to a minimum.  There were days last year that that it was -20F outside and my house only lost 2F between 8am and 4pm when the thermostat lowered to account for no one in the house during the day. 
Lots of advice in this thread.  Some good.  Some not so good.  If you want to solve the issues you will need to look at your house as a "system" rather than just one issue.


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## RJSakowski (Dec 26, 2020)

I would agree that trying to hold temperature to 1/2 degree in an old house is an exercise in futility.  Even if holes contributing to drafty conditions are sealed up, single pane windows will set up convection currents which contribute to air movement within the house.  In addition to setting the thermostat for a longer cycle time, consider the location.  A thermostat shouldn't be located near a hot air register or near a spot where air currents may affect it.  If necessary, consider closing or throttling back hot air registers in the room where the thermostat is located.  Another solution would be to mount the thermostat on a thermal mass.  I would use a shallow box , probably aluminum and a more massive back plate.  The box will tend to shield the thermostat from air currents and the thermal mass will have to be heated/cooled along with the thermostat, creating hysteresis in the cycle.

Our house is also over 100 years old with about 1700 sq. ft. of heated space.   When I originally moved in, there were single pane windows with air gaps and no insulation..  We heat with a wood furnace and at first, I would burn 20 cords of wood in a season.  Blowing cellulose insulation in the walls, replacing the old windows with modern windows, and genearrly sealing up any air gaps have reduced that to around 4 cords/year.

We have a 93% efficiency backup L.P. furnace which is used for heating when mild outside conditions don't warrant building a wood fire or when we leave for an extended time.  We burn about 150 gallons of L.P. a year. Our L.P. furnace is a 120kBtu input/112kBtu output furnace and has performed well for us over the past twenty years.  Even in the early years with poor windows  and drafty conditions, there has never been a problem with short cycling.  The thermostat controls to +/- 1º.


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## RJSakowski (Dec 26, 2020)

Flyinfool said:


> The more research I do into this the more screwed up I think the whole system is.
> 
> I set up a temp probe right next to the thermostat to see what the actual temps are doing.
> The thermostat is trying to hold temp on this old house to within 1/2 degree. the stat asks for heat when the temp drops by 1/2° and shuts off when it reaches set temp a half degree higher, the room then climbs a half degree more while the furnace is in cool down mode.
> ...



I just looked at the installation instructions for the LUX thermostat on our wood furnace.  In addition to the switch on the back for electric or fuel heat, there is a software setting for hysteresis from 1 to 4.  It is accessed by pressing NEXT and HOLD buttons simultaneously while in the RUN position and UP or DOWN to change.  Pressing NEXT will exit. Your thermostat may have a similar routine.


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## pdentrem (Dec 26, 2020)

Last night we watched the comedy movie “The Money Pit”. The older the house, the bigger the pit and bigger the pot of gold required to fix it.
I would hate to think how much I have spent to date on updating this 70 year old house. All windows and outside doors. Added R50 to the attic, 13 bales of R28 to start in the first winter, and 2” foam on the basement walls and the Dri-core panels on the concrete floors. This reduced the bills right away. 
Replaced the antique heat pump with a Bryant Ultra high efficiency furnace, moved some of the duct work around as well, that cut the power bills and gas bills by more than half again!
When I rebuild the kitchen, which is the windward wall, I will strip the wall down to studs and spray foam this wall. It is a total 20% of the outside wall. This will change my cabinets from ice box in the winter and toaster in the summer to something a bit more moderate. Stopping the air entrainment and stiffen the wall. The original insulation is R7 papered on both sides and poorly fitted.
It is an ongoing process and a continuously moving target, as cost to heat and cool keep going up.
Pierre


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## RJSakowski (Dec 26, 2020)

My 110 y.o. money pit cost me $25K and came with 12-1/2 acres of land.  I have put about $100K into remodeling with $50K going into the kitchen (although the kitchen is a world class act).  There is also a very large amount of sweat equity.  The property is currently assessed at $200K which is most likely under market value.  We have a home which is comfortable and reasonably up to date regarding plumbing, and electrical, and is structurally sound enough to outlive me.

Personally, I would prefer the older home built with quality materials over the new home built with skimpy materials by builders cutting corners to boost their profit.  Whenever a tornado rips through the area, the houses n the path look like a pole of pick up stix.  If mine ever gets hit, it will be more like Dorothy's house in the Wizard of Oz.

One definite advantage of buying a fixer upper is that the sweat equity is tax free.  It is a great way for someone starting out with more time than money to build their assets.


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## 7milesup (Dec 26, 2020)

I disagree about the older home and quality materials.  One of the only advantages I can think of regarding an older home is that a lot of the "sheathing" they used were individual boards nailed to the outside walls or to the roof trusses.  I have seen so many "quality" old houses with sagging floors and poorly constructed stairs, not to mention there is not a straight wall or floor to be found.  If installing a built-in, many provisions need to be made for significant irregularities.  A real PITA.  Most old homes have balloon framing also, which is a fire disaster waiting to happen.
To each his own though.  Old houses just are not my thing.  A properly constructed new house provides a level of comfort that I really enjoy.

I forgot to mention that my new house also used --->T-Studs. A new and significant inovation.<--- In fact, my house was the first in the state of WI to utilize them.


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## Tozguy (Dec 26, 2020)

7milesup said:


> A properly constructed new house


or a properly constructed old house that has been properly renovated 

they both have their appeal if the word 'properly' applies. Sometimes the spacious land that an old house is built on is the deciding factor.


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## 7milesup (Dec 26, 2020)

Tozguy said:


> or a properly constructed old house that has been properly renovated
> 
> they both have their appeal if the word 'properly' applies. Sometimes the spacious land that an old house is built on is the deciding factor.


True.  But I do like the 22 acres the my new house sits on.  Ok, ok.  I will quite badgering you guys about old houses.  
All in good spirit....


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## Tozguy (Dec 27, 2020)

7milesup said:


> Short cycling is almost always caused by improper sizing of the equipment. Couple that with an extraordinarily inefficient house and there will be a lot of issues.


Agreed. With a poorly insulated house the size of a heating system would have to be huge for the coldest days of the year in Wisconsin. That would possibly make it too big for other days when the inside/outside temperature differential was say half or 1/4 of the coldest of days, and is a problem that a thermostat can't correct.
If the heating system is indeed too big for even the coldest days then yes that would unnecessarily promote short cycling. Otherwise, downsizing the furnace just to reduce short cycling might make for some cold nights in the hacienda.
Thats why to me a prerequisite for decent performance of any modern heating system (since the coal furnace) is efficient insulation.


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## Flyinfool (Dec 27, 2020)

Coldest day of the year is also why I think this furnace is way oversize.
When it was 25°F below zero and 30-40 MPH wind with a wind chill of near *-*60°F this furnace had no problem with the 10°F night time setback to raise the house temp 10° in under 15 minutes.

There pros and cons to any age of house. That is why there are so many to choose from. After watching my 2 sisters and what they went thru building their houses, by the time the house was built I would not need a house Cuz I would have already killed the contractor.....
There are many features of this house that I really like that you will not have in new construction. On the other hand there are some things that were really done in a way as to be only aspiring to get UP to half A$$. Yes over the years I have had to do a lot of fixing of things, with more yet to fix.


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