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Hot water heating efficiency

I have a hot water radiant system running off propane recently installed in our building. The building is only occupied twice a week.

We have been letting it cool down to 15 C then heating it up to 20 C doing this we have burnt through almost half a tank of propane in a month.

Is it more efficient to keep the building warmer the whole time or let it cool down more and then heat it up on the days the building is occupied?

My thought is that whenever the building is occupied it takes a lot of propane to heat the water and the building back up so were not actually saving any money by keeping it so low. So we would keep it a 18C then heat the building up from there.

Thanks for your help.


  • RobertRobert Posts: 164Member
    You will save propane with a setback that long, but the recovery time will be long as well. Are you using a programmable thermostat?
  • GordyGordy Posts: 8,025Member
    A little information about the radiant slabs construction for the building in question.

    Are the occupied times the same?

    Size of building?.

    As been said radiant has mass depending on the construction detail.
  • jag330jag330 Posts: 6Member
    The building is about 4000 sq ft mostly two large spaces with a few smaller rooms off to the side.

    Occupied times are the same every week and there are two programmable thermostats one upstairs and one in the basement.
  • GordyGordy Posts: 8,025Member
    Types of radiant floor?

    Tube in concrete in basement? Upstairs main floor?
  • GilmorrieGilmorrie Posts: 55Member
    Here is way to look at this: During a whole heating season, your system has to deliver to the building's interior the same amount of heat that is lost from the building to the outdoors. So, by turning down the thermostat when the building is unoccupied, the heat loss is reduced.

    During recovery periods, is the boiler less efficient? No, it is more efficient.
  • GordyGordy Posts: 8,025Member
    Forgetting the mass of the building, and furnishings. being heated, and cooled. In this case money is saved for the little occupancy periods. Short duration setbacks seldom are noticeably fruitful for the loss in comfort. However if the radiant is high mass then it takes a lot of energy to bring that mass back to set point.
  • DZoroDZoro Posts: 354Member
    If it is actually concrete radiant. New boiler should have outdoor reset control system. Let that system work as designed, providing it was set up properly. Do not use programmable stats, maintain constant temp. Hopefully system has a slab/air sensor installed. Much less energy is needed to maintain, compared to raising and lowering concrete temperatures.
  • jag330jag330 Posts: 6Member
    It is heated by wall mounted radiators. The system was installed to replace electric baseboard heating. So no in floor heating was installed.
  • GordyGordy Posts: 8,025Member
    Okay that’s some what of a game changer, and not radiant heat as we know it.

    Rads have mass depending on what type they are. Ci, panel rads etc.

    I’m still in the belief that deep setbacks can be brutal to bring on line intermittently. What is sacrificed is comfort. Call it the cold temp is 70,but the mass of the room is 62, and sucks the heat right off your body.

    You might have to experiment with a setback that satisfies the wallet, and the body when occupied.
  • jag330jag330 Posts: 6Member
    Ok. Thanks for all the help guys. I'll have to experiment with settings and see what works best.
  • DZoroDZoro Posts: 354Member
    Do you have outdoor reset control with this system?
  • jag330jag330 Posts: 6Member
    The installers actually took the outdoor temp sensor off as it was causing problems with the boiler. So the boiler has it but its not enabled currently.
  • DZoroDZoro Posts: 354Member
    Hmmm, If you maintain constant temp in the building then that sensor will be your wallets best friend. So find it interesting that it was removed..... Can you provide a picture of the system?
  • BrewbeerBrewbeer Posts: 459Member
    Deep setbacks become easier to manage if the system has a high radiation density.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread:
    System Photo:
  • ZmanZman Posts: 4,291Member
    Installers that don't understand outdoor reset think it causes everything that plagues mankind.
    Reconnect the outdoor reset and don't go with such an extreme setback.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • GordyGordy Posts: 8,025Member
    edited December 2017
    If this is a CI boiler with outdoor reset then proper piping/ mixing valve needs to be in place for boiler protection of cool return water temps. Especially with your setback regiment.

    If the CI boiler gets a constant flow of sub 135*return water it will soon rot the HX due to condensation.

    Some pictures of the boiler piping are in order. This may possibly be why the ODR was disconnected. However I’d be willing to bet as others said it’s lack of understanding.
  • jag330jag330 Posts: 6Member
    I'll try to get some pics for you guys. I'll get that sensor reinstalled asap. I don't believe there are any mixing valves in the system. But it is a aluminum core stainless steel sleeved heat exchanger on it.
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