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marcqs
thermostat set backs for boilers
marcqs

My power company suggests setting the thermostat back by 10 degrees at night or when away from the house to save energy in winter. I am wondering if this advice is for forced air heating rather than boiler/radiant heating situations? I have a 900 sq ft house with original cast iron radiators and a newish (6 year old) boiler. I have noticed that when I turn back the thermostat 10 degrees, it takes my boiler 3-4 hours to get the house temp from 56 to 66 F. Someone told me that when a house is heated by radiant heat, the stuff in the home - furniture, walls, etc. will hold the radiant heat and contribute the heat back to the room, or help maintain the temperature of the house at least for a while. So I was wondering for a house heated by radiant heat, does it save more energy if a person maintains a modest temperature- in my case, maybe 62 or 63 F at night or when away from home, and then increase to 66 F when people are active in the house? Or is there other advice or strategy for saving energy when the heat source is radiant heat vs forced air heat?

Many thanks for any thoughts on this question!

Fencepost
Re: thermostat set backs for boilers
Fencepost

You are still saving energy, even though your boiler is running continuously for 3-4 hours. The total running time of your boiler inclusive of the time when the thermostat was set to 56 degrees PLUS the time it took to get back up to 66 degrees will still be less than the total running time during the same period if you left it at 66 the whole time. So there's still an energy savings there.

However, there isn't a comfort savings. The advice from your energy company is worthwhile if you have a forced air system. Forced air systems heat the air in the room more quickly than radiant systems, but radiant systems make you feel warmer when the air is cooler, as long as there is an unobstructed line of sight between the radiator and you.

If you find that the length of time to reheat the air to your desired temperature is too long, then don't set the thermostat back quite so far. You'll need to experiment to find out what the acceptable setback temperature is to achieve an acceptable recovery time. The energy savings won't be as great, but there will still be savings.

You may be able to improve the recovery time somewhat by using a portable fan to blow air across the radiator in the rooms that you are using.

NashuaTech
Re: thermostat set backs for boilers
NashuaTech

marcqs,

Glad to see you have cast iron radiators and hydronic (hot water) heat in your home! In my opinion this is the best way to heat a house, since the rads stay hot and continue to radiate heat into the living space long after the boiler has shut down once the desired T-stat temperature is reached---then they continue to radiate their heat, often for hours without any further fuel expended.

I think the key to your situation is to make sure you have a T-stat with "setback capability" installed on your wall (usually the living room); a setback T-stat has a tiny little brain inside of it that can be programmed to keep the heat higher & comfortable when occupants are in the house----and to set-back to a much lower temp (low 60s, etc.) when the occupants are at work & school, etc.----clearly, there is no need for heat in the 70s when no one's home--they can be programmed to initiate the re-heating of the house perhaps 1/2 hour before anyone gets home from work or school---so you'll never walk into a cold house---there is an "override feature" on these programmable t-stats that can be activated if you get home early on a particular day or the kids have no school that day!----this is a great fuel-saver and money-saver!

These T-stats are smart enough to be set a multiple intervals of time throughout the 24 hour period thru the week, along with weekends, etc.

Another method that some homeowners use is to install ZONE VALVES with their corresponding T-stats in different parts of the house; especially if you have a large house, bedrooms on multiple floors, etc.---- these different parts of the house can be set up with their own t-stat that will heat only that part of the house that is being used----a great fuel-saver.

Up to 6 or more Zone valves can be installed to run on the same existing boiler, depending on the size of the house & if various parts of the house are unoccupied most of the time, again with programmable T-stats for each part of the house---with hot water heat, there's so many things that can be done to add comfort & savings to a home!

The third consideration is to make sure you have adequate INSULATION in all the exterior walls of your house, along with preferably double-pane storm windows that will keep the heat IN THE HOUSE & save greatly on annual fuel bills; if insulation is needed, it can easily be blown into the exterior walls from the outside of the house by an air-pressure truck at a reasonable cost that will save on fuel bills for many years into the future.

Fencepost
Re: thermostat set backs for boilers
Fencepost

I just remembered something else. You mentioned that you keep your thermostat at 66 degrees. This is quite a bit colder than most people keep their houses. Typical is 72 degrees, with a normal range of 70-75 degrees.

Since you're already keeping it colder than normal when you're home & awake, when you leave you don't need to set it so far back as the energy company's recommendation. A typical setback temperature is around 60-62 degrees.

And as Nashua Tech said, weatherizing your house (insulation, draft sealing) will provide the best return on investment. Even if adding insulation to exterior walls isn't feasible due to the construction of your home, adding insulation to the attic (12-18" or more) can make a huge difference (be sure to seal any penetrations -- wall/ceiling joints, electrical wires passing through top plates, around recessed fixtures). If any portion of your home is over unheated crawl space, floor insulation can make a big difference, too. Don't overlook drafty doors; adding weatherstripping or replacing a worn door is a good investment of time and money.

Besides energy savings, weatherization makes your home more comfortable by evening out the temperature throughout the house (drafty areas are cold areas!) and reducing the temperature swing between the heating system turning on and off.

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