Pulse & Glide Furnace

[aalb1]

I'm sure we are all familiar with the term pulse and glide when it comes down to driving habits... but what about furnaces? Does anybody have any suggestions on how to Pulse & Glide with a furnace?

As of now there is a 20 degree difference between the furnaces high and low settings currently my low setting is low enough to take a shower with about 90% hot water and 10% cold water (my wife hates me for this).

With winter right around the corner and oil still pretty high I'm thinking of increasing the high/low difference if it will save on oil consumption. Any suggestions?

[GasSavers_Erik]

Leaving the heat off/very low when you are not at home or while you are sleeping will save you money.

Perhaps you could buy a programmable digital thermostat with an ultra low setting that lets you dip down to 40 degrees at night/while you are at work and then bump it up to 65 during the late afternoons/evenings when you are around. This would keep the pipes from freezing and also keep your refrigerator compressor from running as often.

[Snax]

I know that this not what you are asking, but there is such a thing as a pulse and glide furnace: It's called a masonry stove. Essentially it is based on the idea of using a large thermal mass to store energy from a shorter hotter burning fire. The fire is allowed to burn as hot as conditions allow, and the sheer mass of the stove absorbs the heat, which over the course of the next 6-8 hours slowly radiates it out into the room.

They are not cheap to put in, but from what I have read, a well designed one can comfortably heat a home on less wood with far more even and less extreme heat output. In other words, except for the doors, the mass is never heated enough to be too hot to touch.

[Lug_Nut]

Increasing the high / low differential will save IF the low is lowered, but not if the high is raised.
The standing heat losses, those losses when water is not being used, are greater when the temperature differential is greater. Heating the water to 190F and letting it sit there in a 60F room will drop 10 degrees faster than is that water were heated to only 160F and left to sit in a 60F room.
Dishwashers that require hotter water for sterilization may limit how low you can go, but otherwise, set the low heat limit as tepid as you can stand, and set the high just 20F above that.
A lot depends on the mass of domestic water being heated. Mine is oil fired and tankless. There is no large volume of water remaining at hot settings for the 23+ hours I am not using it. However a 40 gallon hot water storage tank will need to be kept hot because it can't react as quickly to instant demand.

Be wary of the setback thermostats for space heating. No heat means no water circulation through the base boards. Pipes in exterior walls are at the average between the inside and outside temperatures. A 50F interior and a 10F outside can let the pipes in the walls drop to below freezing. We had several ice plugs form that prevented any water circulation for the week or so until the cold snaps were over. Fortunately for us the pipes didn't burst during these episodes. We now run a glycol mix in our baseboards to allow low set back and prevent freezing.

[itjstagame]

It's a sealed system so there's no reason to not use glycol, good idea!

[JanGeo]

It's a sealed system until the heat exchanger between the heating water and the hot fresh water developes a leak. If you really want to do it right you should add a timer switch into the hot water circuit so that the furnace doesn't keep itself hot for water during the night or daytime when you are not home. In the summer it can save almost a tank of oil because it only takes about 5 minutes of running to bring the water up to usable temperature. In the winter it will be less but still help during the daytime. Keeping the furnace at as low a temperature as possible and still hot enough to provide you with all the water you need will maximize your fuel savings. If you really want to save you heat couple the shower drain pipe to the cold water intake pipe of the furnace hot water circuit and use the drain water to preheat the cold water coming in from the street. Nobody does this but it should raise the water temp several degrees.

[GasSavers_RoadWarrior]

I'd pony up for Polyethylene Glycol (think that's the safe one) just in case for anything in the house, you never know if it's gonna develop a stealth leak into your kitchen cupboards or what.

[JanGeo]

Only problem is a standard oil furnace holds about 40-80 gallons of water in the heating jacket - that comes out to a lot of antifreeze. Would probably help with the corrosion in the lining and conduct heat better in the radiators. Did a friends sailboat earlier this month with the RV type safe stuff 12 gallons - lots of pipes with water in it in a 42 ft sailboat.

[Lug_Nut]

Originally Posted by JanGeo

It's a sealed system until the heat exchanger between the heating water and the hot fresh water develops a leak.

The heating water is pressure reduced to about 20 psi. Our well pressure cut-in is set at 60+ psi. Any leak will be from fresh into heated. Additionally it's non-toxic, but not tasty, so if there were a leak allowing transfer of poly-pro glycol into the hot drinking water it would be noticed pretty quickly and well before any possible poisoning risk.
It took two 5 gallon pails to protect our 1300 sq.ft. two story, full dormer cape against freeze down to -10F. If the electricity goes out for long enough, and it's cold enough, it'll still eventually freeze, but long after it would have otherwise.

I suspect a boat outdoors will see colder temps than the pipes in the walls and would require a greater concentration or ratio.

[JanGeo]

Yeah we have really low town water pressure - you can stop it with your thumb out of the faucet so there was a little back flow once in a while and man that water in the heating system turns rank after a few years.

Only 10 below should be easy and your heating system should not see that low a temperature very quickly.