Programmable T-stats with high efficiency furnaces??

[tdkkart]

Our last home was a 1000sq/ft ranch with, if I recall, a 90KBTU furnace. I believe it was an 83 or 87% efficient model, still used a chimney with draft assist fan. We used a programmable T-stat to turn it down 6-8 degrees when we were at work and when sleeping. Near as I could figure it was worth approx. 30% savings on the natural gas bill. Recovery time was short and the house was comfortable.

BTW, we both work nites, so during the week the T-stat was setup to come up to 68-70* at 8am and then drop back to 62* at 2pm. Weekends were obviously on longer schedules.

Our new place is 1500sq/ft multi-level with a new 93% 60K furnace. Using the same T-stat schedule as before the furnace seems to cycle alot and the house never really seems to get up to "full operating temp"??
The last few days I've been running the T-stat on "hold" at 70*. The overall temp is much more even and the furnace seems to run much less.

I realize that the "modern" heating philosphy is to blow cooler air more often, maybe I'm just not used to it yet. The furnace was installed Nov 19th so we haven't gotten our first gas bill yet, maybe I'm just a bit nervous over nothing??

Do I need to make adjustments to my heating philosphy, and or my thermostat?? Does the programmable T-stat even make sense in our application??

 

[Torque1st]

I have done the same thing with my heating equipment. We have upgraded the furnace and have a programmable stat. Basically you should be OK. Remember it is COLD as hell outside right now. We have not had this type of cold for awhile.

Thermostat temp displays and measuring can be off by a few degrees. Check your temp display with a known good thermometer.

Some thermostats have a demand factor that must be set. Check your instructions. Some digital ones "learn" that function. The digital stat actually reads temperature in the tenths of a degree and watches the rate of change in the house.

Check the humidity levels in the new place, a little humidity can make a big difference in comfort. Humidity can be lost thru leaks and air exchange with the outside. Humidity is also lost when other appliances like a dryer, hot water heater, bath or kitchen fan vent to the outside.

 

[Torque1st]

Another thing. Make sure all of your ducts are good with no leaks. You may need to adjust some of the runs to balance out the system. Adjustments can be made with dampers in the ducts or at the registers. People have a tendency to mess with the registers tho.

I have one duct that leaks up into the wall and into the attic. I can see a spot on the roof when we get a light snow. I just need to get some spray foam and seal it up better.

 

[Tom2]

Thats one thing I dont like about modern thermostats. They try to keep the house within exactly one degree - and no heat anticipation setting. If you have a drafty house (like mine) the result is way too many furnace cycles which is a waste of energy. (you have to reheat the heat exchanger each time before the blower runs)

I was able to program mine to only cycle twice per hour. Works well for my situation.

 

[2LTim]

Tdkkart:
As Torque1st eluded to, it's been a bit chilly outside lately, even here in Iowa. We built our dream home ten years ago, just suth of Des Moines and installed a Geo Thermal Heat pump. The system came with a programable thermostat, and we have tried using it both ways. With the Geo, when you request a temp rise more than 2 degrees over the current room temp, it kicks in the "emergency heating" coils, to keep from driving your loop temp too low. This function really makes the meter spin! As it turns out, the system uses less power holding a steady temp all day than it does if you let "cool down" when not occupied.
The Geo keeps the house very comfortable, but if you come in from outside and want to warm your feet, you are waisting your time putting them on a register. The air coming out is luke warm at best. You just have to enjoy that nice toasty warm feeling of not sending Mid American Energy a huge check every month! In the summer on the other hand, you could hang meet in here. The AC is second to none!

 

[hidollartoys]

Kart, If your numbers are accurate then your first house had two times the standard btu requirements at 74 btu's/sqft. Should be 35 - 40 btu's/sqft for a house that is "newer and well insulated". Your current set up is right at the lower limit of the design parameter @ 35 btu's/sqft. Your best heating effency will to be set the thermo at the desired comfortable setting and leave it there. Your system is not "large" enough to over come the ramp up without sacraficing the comfort and probably cost more in the long run. As torque stated you may also have air distribution issues because the air handler (blower) is also right on the edge of being enough especially if the original installer did not actually balance the duct work. Most installers rely on old rule of thumb duct sizing which compromises the newer equipment's air moving capabilities. Most HVAC guys still talk in "tons" of blower and they should be more aware of actual flow (CFM) @ defined static pressure. Just like every other part in the furnace the new blowers are also being maxed out and static pressure is extremely improtant. It used to be that the blowers were not the weak link with more than enough capacity but Mfgr's are designing the "system" with total efficiency in mind. With the new Federal standards this is even more critical and now Mfgr's are providing "matched" systems that will only work if ACCURATELY sized. The days of "rule of thumb" are essentially over. Used to be that bigger was better. Today the equipment is designed to be more efficient by running longer at each heating/cooling interval making accurate sizing imperative.

 

[Tom2]

Yea..It can be tough to get a furnace sized properly. Im probaly 20,000 btu oversized at my house..(100,000 btu for 2500 sq ft - low ceilings) Thats what the furnace salesman told me I needed. He was wrong, and so was I.

Im a car guy, so bigger, more power, always sounds better. Not the case at all with furnaces. Especially with fuel prices being where they are.

 

[Torque1st]

One thing I do with my program is set the times so that if I want it 70°F at 6PM I set the furnace to go to 70°F at 5:30PM. I also run the shut down times 30 minutes in advance also. My system is undersized due to house additions from the original but I did upgrade insulation. When I upgraded I knew the old furnace would keep up with my needs so I sized the new furnace to the same OUTPUT figures. Now I use a 92% 80000 Btu per Hour, Output Heating Capacity 74000 Btu per Hour system on a 1550 sq foot house and it works well. -About 48 BTU/sq ft. I will be adding to the house size soon and doing a window upgrade so who knows how it will work then. The original furnace seemed to be overkill.

 

[SteveU]

I adjusted the anticipator setting to the lowest number which results in fewer on-off cycles. There should be information on how to do this in your owners manual. How I have it results in a 2 degree spread, it kicks on at 67* where I have it set & gets it up to 68* by the time it stops running. Before it would kick on & off & the temp wouldn't change.