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Programmable Thermostat for Radiant Heat

This past summer we moved into a home that was built in the early 1900s. The home has cast iron radiators and the water is heated by an oil burner and is controlled my a manual Honeywell thermostat. In my previous homes I have had programmable thermostats and set them lower during the night to reduce my energy bills. I am thinking about installing a programmable thermostat and do the same thing. However, in talking with some neighbors they seemed to think that would not be the best idea because of the nature of this type of heat system. They said that it would be better (use less energy) to keep the temp constant because with the water cooling down during the night it would take more energy to heat it back up in the morning than just keeping at a steady temp all night. It seems to me that it would use less energy by turning the temp down for those 6-8 hours during the night even though it would have to work harder to bring the water back up to temp. So which method is more energy efficient for this type of heat system?


Re: Programmable Thermostat for Radiant Heat

Was your previous heating system a forced hot air system ?

That type of system is perfect for set-back thermostats since forced hot air has a rapid response. You can literally set the thermostat to start heating minutes before getting out of bed and benefit with immediate hot air warming up things.

With a hot water system you would likely need more time for the hot water system to come up to temperature and begin warming things up before getting out of bed. In theory it would seem that turning down the temperature and not using extra fuel would be beneficial ,depending how long it takes for hot water systems to respond for heating things up would determine if there is a benefit.

Hopefully someone that's more experienced with hot water heating systems would also have some insight.:)

Re: Programmable Thermostat for Radiant Heat

Yes my previous heating systems were force air systems and were very quick at heating up. This water based system takes about 30 mins or so to get up to temp and that is why I am asking the question. I would like to keep the fuel oil bill as low as possible while keeping the family comfortable.

Thanks for the response,

Re: Programmable Thermostat for Radiant Heat

Canuk is correct!

Hot water systems take a while to get up to speed.

The first thing I tell homeowners to do if they want to save big bucks on fuel bills & still be comfortable, is to look at the insulation.

You should have R19 in all exterior walls & R40 in the attic.

The old saying that you can heat the house with a candle if you have a very thick insulation envelope is nearly true.

If you lack insulation in exterior walls, they have trucks that blow in cellulose for a few hundred $$$; you can increase insulation in the attic & cellar/crawl space as a diy project for a few $$$.

A more widely used method of boiler control that's all the rage these days is called OUTDOOR RESET.

Tekmar 256 and Honeywell AQ 475A controls and others make electronic boiler attachments that constantly sample the outdoor temperature & within limits tell the boiler to lower or raise the boiler water temperature.

The basic idea is that most boilers operate at 180-200 degrees water temp to be ready for a call for heat from the thermostat.

This is ok for very cold days (design temperature) but wasteful of fuel especially during not so cold days, and mild days; the not so cold days actually make up a large portion of the heating season, so the boiler water doesn't have to be at 180-200 degrees water temp during these periods.

Google "outdoor reset" boiler for further info.

Your heating technician would have to come in to look at your heating system to see if this can be done, the cost involved, & how quickly you could expect a payback on your investment.

These controls often have the circulator going most of the time as a means of moderating the room temp.

Most of these controls are designed for boilers that operate at lower temps; older boilers are not designed to operate at temps below 130 degrees, since they would form condensation on inside boiler parts.

So your heating tech may decide that an outdoor reset is not suitable for your boiler; however, a 5% to 30% fuel savings can be realized if you can find someone in your area that is experienced in installing these controls, and feels it's worthwhile.

You may have to consult the Yellow Pages under "Heating Contractors" to find one.


Re: Programmable Thermostat for Radiant Heat

So are you are saying that a programmable stat will not help and I should only look into possibly having an outdoor reset installed?


Re: Programmable Thermostat for Radiant Heat


No, I'm not.

Setting back the T-stat when you're away at work or overnight, if it's not too cold in the house will always save you some money on fuel bills.

It's just that your heating tech will be able to look at your boiler & suggest the best way to go, depending on the style boiler you have & its attachments.

He may spot some things that you're overlooking.

Do you clean the boiler each fall; is the boiler over-fired, can it be down-sized in heat output by putting in a smaller nozzle; is the boiler over 15-20 years old & only 50% efficient?????

For example, some boilers have a "tankless" domestic coil inside that provides the hot tap water; these boilers have to maintain a constant high temp of ~180 degrees simply to have the hot tap water ready.

You can get further feedback on this at heatinghelp.com (click onto "the Wall") and also HVAC-talk.com (residential heating) or doityourself.com (boilers).

Have ready info on the make of boiler, its age & if you have a tankless coil.

Re: Programmable Thermostat for Radiant Heat

Thanks for the help Jack. I will check out those sites.


Re: Programmable Thermostat for Radiant Heat

I live in the north-east and have an older house with cast-iron radiators served by a boiler.
I have an older Honeywell programmable thermostat that I installed many years ago.
It was not a special version - it was an off-the-shelf product from a home improvement store.
When installed, there was a switch or jumper on the back that was to be set for my type of furnace. I believe it "told" the thermostat that the response time was slow. I seem to remember that there was wording about a 1 hour cycle time.
It works beautifully. It "backs up" the required amount of time and provides the temperature set at the time programmed.
I know this is an old thread - but I'm looking for a replacement and this was one that the search engine found!
Hope this info helps - stay warm.

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