High Eff Furnaces And Home Comfort?

Braun Builder's

I built a custom Home for a customer last year finished in feb 08
4300 sqft Very open first floor, Cullouse insulation, LOe ,argon
Very tight and Eff
2 stage in the basement
variable in 2nd floor furnace closet
Honeywell Vision Pro Stats
Electric air cleaner's , Humidifier's Ect
Home owner says they are comfortable in the house between 63 and 65 deg. Last winter they just left temp at 63.
They would like to program the stats to try to take advantage of the big money spent on the furnaces.
My question is how much of a temp set back is advised with these systems.

westernhvac

The vision pro tstats have intelligent recovery so go for whatever you feel comfortable with. As long as there is enough recovery time between program periods then they should be ok.

hf05

You really should'nt drop it anymore than 3 or 4 degrees at night.anymore than that and your not coming out ahead,due to the unit running longer in the morning to bring it up to temp

flashheatingand

Mind you, this is just my opinion.... There is nothing wrong with long run times with the appliances. It's actually better for the unit to run steadily for a long time than to cycle on and off several times throughout the day or hour. With convection heating systems (ductwork) I believe use it when you are on the premisis, keep the temps to a minimum while the space is unoccupied.

The furnace isn't an animal that will tire out after x hours of usage. They do not work "harder" if it has to raise the temp 5 degrees or 25 degrees, it will just run longer. Which isn't a bad thing.

If someone can explain why one should not let the temp drop say 10 degrees below the normal set point, I am all ears. I am talking about convection heating, not hydronics. That is a different breed of cat.

Braun Builder's

This pretty much wraps up my general question I have been searching.
I have not been able to find any evidence of what degree of temperature drop is the most Eff.

I would think that in the shoulder months a larger temp drop(maybe 10 deg) would be ok as the house is not going to loose heat near as fast and recovery time will be quick.

In the cold months a smaller temp drop (maybe 3-5 deg)

You maybe loosing consistancy room to room temp wise as the house temp is cycling from cold or warm in a smaller time frame with the larger temp drop.

With the 2 stage and variable speed furnaces isn't the point of them to avoid using the full output and that's where your savings comes into play?

I am just a builder but most every house i build is becoming more energy Eff so this info would be helpfull

hf05

The point here is trying to save fuel.RIGHT, if u drop your stat 10 deg regardless of ambient temp you will be consuming more fuel period.As for 2 stage units i don't know what you have,but on average your low fire will only run 10 minutes on low then jack up to hi ,carriers are 16 min.Most half decent stats will even reccommend a 3 or 4 deg swing.Or try it for a month at 10 deg and see what happens..

Braun Builder's

I don't think this is correct as if you only drop the temp 3-4 deg then you are more than likely going to have to meet that temp and maintain the 3-4 deg temp drop. There seams to be quite a variable and no one knows for sure the correct answer I am even having trouble finding support for the energy star claims. I am going to have to send am email to mythbuster's
see if they can test this

flashheatingand

I definately don't know the right set point. If the engineers say 3 to 4 degrees is best so be it, it is likely that they actually did studies, whereas most heater dogs are busy worrying about how to get a duct from point a to b, or where to get the discombobulator for Mrs. Jone's old furnace.

One of the "compliants" about convection heat is that it is quite inefficient. If one truly wants to heat efficiently, they would heat the building as opposed to heating the air. Nothing so bad about air to air it's just not the most "efficient". Based on thatwqe, you might as well only use the energy while the building is occupied and keep usage to a minimum while unoccupied. That is how to get the most use from the programable t-stat and you probably can save more than 30% with a programable stat, it just needs to be tweaked. Intelligent recovery is a nice feature.

The correct number is something the homeowner needs to find out for themselves. They need to be comfortable. My reccomendation is to leave the factory settings for one month, and adjust to 10 degrees drop. The bill will tell you what you can do.

Dan13

If the house is as tight as you claim I don't see any why you shouldn't be able to drop the stat back 10 degrees since the house probably isnt going to lose 10 degrees in 6-8 hours time anyways. Now if the house was not as tight then I would not set the stat back anymore than 6 degrees due to the house losing that 6 degrees in less than a 6 hr period and once the furniture, flooring like tile will get colder faster than it will get warmer so if you were to set the stat back in a home that has a high heat loss it will cost you more to heat in the long run due to the high infiltration rate. My home is fairly tight and I am lucky to lose 4degrees overnight even though I set my stat back 5 degrees and it generally loses about 2degrees in maybe 1-1/2hrs give or take a few minutes. So all in all it is all dependant on how tight the home is will dictate the amount of setback as will heat loss dictate the amount of setback.

mo-flo

i would think that this would have to of been taken into consideration when sizing equipment if you are worried about recovery time....efficency i would want mine sized right and put it were i wanted it at on stat and leave it there..JMO.

dlcj

I have actually thought of doing that too.

I bought a programable honewell (for full elec. heat pump) back in the summer too but its hard to get a good average cuz the weather temp changes to much here. May take a year to know if i saved any money but at least i dont have to think about changing the t-stat all the time and its more comfortable now. Winter i set the temp and 63 from bed time to 1 hour before waking, then 71 for 2 hours while we get gone then 58 during day (just to keep it off, it never drops that low inside during day) till 5 back to 70 till bed time.
Summer cool at 68 night, 72 morn, 85 day ( it never comes on even on 95* day) then 75 evening. Unit acually runs more at night in summer than day, brick house
We never use the cool and heat feature. The preset 3* temp from heat to cool is too close and not effecient if you ask me.