Furnace Gurus ?

[Paul Clark]

If the thermostat in the house is usually set for 68 - 70 degrees, how low can you turn it down at night and have it come back up in the morning and still save some $ on the heating bill.
Is there some point where the cost of raising the heat negates any savings you might have by lowering the heat overnight?
Hope I asked that correctly.
Thanks
Paul

 

[klrv6]

Computer

I bought one of the Honeywell computerized thermostat units It takes your settings and "learns" how long it takes to achive that temp. I have day/night weekdays and weekend settings. Saves $$$$$$ I paid like $80 for it years ago.

 

[turbosam6]

Generally no more than 3-4 degrees, anything past that and you spend more than you would have just leaving it set where it was.

 

[Little6pack]

Go to home depot or lowes.. I got 3 of the same that you can set up to 4 times a day plus they have an override incase you need it asap.

We have it come up in the AM & then off for the day until the kids come home. Then come on again at 7pm for a last blast before bed..

Like mentioned I would not vary more than 5 degrees.

 

[BJM]

In fact there should be no limit to how low you can set it. The key thing is to avoid any overshoot in temperature as the heat comes back on. It hits -30 in winter here and my thermostat drops to 50F during the day. The Honeywell knows how long it takes to warm the house back up again and slowly ramps the set point back up in time for when you wanted it warm again.

The lower the house temp the better, the heat loss is in direct proportion to the temperature difference inside to outside. At -30F, there is ~100F difference and heat will leave my house approximately at a rate of 7.5 kW. If I can knock the difference down to 80F, the leak rate is now 6 kW.

Your furnace is most efficient while running and when the heat exchanger is at full temperature. The hotter the heat exchanger, the more heat is transferred into the house air rather than leaving the house as warm exhaust.

So my house temp will drop from 70F down at 8:30 AM to about 55F around 2PM when the thermostat begins the ramp up again for 4:30 PM to be back at 70F again. During the ramp up the furnace is slightly more efficient since the air its warming is cooler than normal so even more heat makes it out of the heat exchanger.

Its commonly thought that lowering the temperature too much somehow might cost you more, that there is some sort of sweet spot for energy savings. This is not true. It boils down to your tolerance for having the house cold. My aquarium heater cannot keep up when the room cools down too much for instance. The key thing is overshooting the set point which definitely wastes energy.

 

[turbosam6]

All manufacturers I've dealt with DO NOT reccommend running a residential style furnace below 55 degrees. Running below 55 degrees allows condensation to form in the heat exchanger, which is bad.

BJM, I understand what you're trying to say, but what you must remember is not only are cooling the house down you are also cooling everything in it, and that must be warmed up again when your heat comes back on. You might be able to heat the air in the house back up relatively quickly, but it will cool faster once the cycle ends due to the walls, floor, furniture, etc. being cooler.

Your furnace runs so much to catch back up you have to be spending more on power/gas than if you let it stay where you normally keep it. Try it and see what happens.

 

[BJM]

Most of the people on this list have a much milder winter than where I am and some of what I say may be somewhat different. In my case the cool down of the house from 70 to 55 takes place in 6 hours. The heavy objects in the house barely change. Upon entering my house at around 58F one time, the furniture was still fairly warm, the outer walls and the air are what cooled off fastest. So I still save energy. The potential energy contained within the furniture doesn't change nearly as much.

As far as condensation goes, all high efficiency units I am familiar with (and they may be more common here) have 2 sections to the heat exchanger, one section of which is always stainless steel. They are condensing style furnaces. They always have water collecting in them. They drain water when running like an air conditioner. Here at least, they are easy to spot since they do not require chimneys. They use side wall exhausts and a powered fan pumps the exhaust outside. The temperature of my exhaust is barely warmer than the air in the house, the exhaust is soaking wet and forms an enormous 20 lb stalagmite of ice right below it in January.

Where I live, people have largely gotten rid of non-condensing furnaces since they are inefficient and going from mid 80's % efficiency to mid 90's% is worth hundreds of dollars per winter.

If you have a non-condensing style furnace then I would agree you should not drop your house temp too much, but you would still save energy.

 

[turbosam6]

Crap, how cold is it there? My house won't drop 15 degrees on a 20 degree day in 6 hours with the windows open!

When we install furnaces in the winter time, the house is without heat all day and we are in and out sometimes with the door propped open, and we still only see maybe a 10 degree drop.

It must be really cold there huh?!?!

 

[BJM]

I am in Ontario. Where are you located?

In a normal winter it will go below 0F at night for maybe 2 weeks at a time. -30 on several different days, the coldest I have seen is -40(F or C). I use block heaters on my cars almost all winter. If you lose heat in your house its pretty critical since the pipes will all freeze within 30-36 hours if its cold out.

We have probably the biggest temperature range of any where I have seen, the temperature will occasionally hit +100F in the summer. This summer it was mid 90's for several weeks which is pretty hot for here.

Normally the Buick is off the road all winter, but once I had the Buick out one time at -20 and totally clear roads. It was cool, the Scanmaster gives up on the air temp sensor below +10F, it just blinks. I had to turn the boost down somewhat to prevent knock. Spool was instantaneous, it drove just like a N/A motor, it was so weird compared to July and humid when it feels so soggy.

 

[Lee_Burough]

I am in Ontario. Where are you located?

In a normal winter it will go below 0F at night for maybe 2 weeks at a time. -30 on several different days, the coldest I have seen is -40(F or C). I use block heaters on my cars almost all winter. If you lose heat in your house its pretty critical since the pipes will all freeze within 30-36 hours if its cold out....Snip....

The coldest I've seen in Wyoming as a boy and youth was between 30 & 40 below zero. Then, there is the wind....Tell them about the wind BJM....Supercooled is an understatement!

I'm sure our houses are not built to the same standards as yours in Ontario, and it sounds like the HVAC equipment isn't either. We are comparing apples and oranges here

I've worked outside in -20 degree weather....I don't want any more of it, I'm going to move to Texas

 

[BJM]

Then, there is the wind....Tell them about the wind BJM....Supercooled is an understatement!

I once walked to university in a howling wind. I later looked up on a wind chill chart that the equivalent static temperature was -92C!!! Without a hat a person would simply pass out if they tried to stick it out. Its not like we get a month of that though. Usually if its that cold the cold snap will break and the temperature will come up above freezing which in January is a celebration.

Actually I found the heat in my Buick was better than my normal winter car a 97 Bonneville.

 

[Lee_Burough]

I worked with a die hard runner in a hospital in Alaska. He was out running one day and got the end of his P**is frost bit during one of his runs Cold is unrelenting, and besides that, it never goes away.

Sincere apologies for hyjacking your thread

 

[Big Stu]

If the thermostat in the house is usually set for 68 - 70 degrees, how low can you turn it down at night and have it come back up in the morning and still save some $ on the heating bill.
Is there some point where the cost of raising the heat negates any savings you might have by lowering the heat overnight?
Hope I asked that correctly.
Thanks
Paul

I have been doing hvac work for a LONG time now. Get yourself a programmable thermostat and set it where you want it. A furnace that condensates and drains water is a 90 percent or greater efficiency furnace. It gets cold as hell here in arizona(yeah I know, arizona) sometimes 20 below. My Home depot el cheapo $20 dollar thermostat has done nothing but save me money every month. I think anything over 5-7 degrees is too hard on the furnace to raise back up to room temperature. Just my well educated opinion.

 

[BobbyBuick]

intelligent recovery will internally check the cycles to determine automaticly and preshot the temperature.I turn mine to 45 from 7:30 am to 5;30 PM during the week and it generally never drops below 60 in that time. due to taking care of r values and infilltration.With raising gas costs we are really pushing duel fuel HP on natural gas right now also set back t-stats humidifiers and variable speed blowers are very good investments to save money.On a fossil fuel furnace i would set back to 60F or maybe 55F no more than that.Also dont bother going that far if it isnt for any period of time.knock it down before you leave in the morn 30 minutes to 1 hr and set it to be back up as late as possible.
Sales manager Airtron heating and A/C
Dayton division 30yrs in 2006

 

[BJM]

Just for comparison, I have a 2000 ft^2 house and I have a 83000 BTU/hr output furnace. Just wondering how that compares to others.

 

[TR Custom Parts]

Since we have some HVAC experts on here in this thread, hope I can do a little hijack.

I went to put in a programmable t-stat for my 2 zone forced hot air oil burning furnace about 2 years ago when I bought my house. Apparently, what I thought was the usual T87 t-stat is actually older than that and is not compatible with any of the programmable t-stats. Honeywell verified that. My house was built in 1969 and has a Honeywell W737 Zone control so I guess that has to be replaced first so I can update the T-stat??

Have seen some of these controls on ebay - http://cgi.ebay.com/Brand-New-Honey...ryZ41988QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Would this work for me? Doesn't look too hard to install.

 

[Big Stu]

Since we have some HVAC experts on here in this thread, hope I can do a little hijack.

I went to put in a programmable t-stat for my 2 zone forced hot air oil burning furnace about 2 years ago when I bought my house. Apparently, what I thought was the usual T87 t-stat is actually older than that and is not compatible with any of the programmable t-stats. Honeywell verified that. My house was built in 1969 and has a Honeywell W737 Zone control so I guess that has to be replaced first so I can update the T-stat??

Have seen some of these controls on ebay - http://cgi.ebay.com/Brand-New-Honey...ryZ41988QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Would this work for me? Doesn't look too hard to install.

That honeywell board will work for you if your zone dampers are compatible to it. I put in lot of zone systems and it's not always as easy as some may think to get everything wired and working properely. Any programmable stat works with that board on e-bay. Unfortunately I am not famililar with the w737 to be able to tell you exactly what you need to get as far as a thermostat. Best bet is to call honeywell's tech line and ask them what they recommend if anything. You might be able to get something that will work, I don't know.

 

[TR Custom Parts]

The zone damper motors don't have any info on them so I have no clue as to what they are! Just two wires going to each of them. See pic of damper motor and the zone control. Talk about ancient.

 

[Big Stu]

The zone damper motors don't have any info on them so I have no clue as to what they are! Just two wires going to each of them. See pic of damper motor and the zone control. Talk about ancient.

Wow! I don't even recognize those at all, but you're right, they are definitly very old. Hmm..... any numbers or letters anywhere near them?

 

[TR Custom Parts]

Nothing that shows anyway. Would have to pull one off to see if it has anything on the backside.