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Boiler takes long time to heat house

michael123
michael123 Member Posts: 5
Hi,
I have a hot water 75K btu gas boiler heating system that heats my 1,400 sq ft semi attached home.
The home was built in 1900s and is not very well insulated. I have cast iron radiators installed throughout the house. I recently had this new boiler installed. It takes about three hours to heat up the house in the morning from indoor temperature 62 degrees to 72 degrees.
The boiler is programmed to heat the water to 170 degrees and start cycling.

I know insulation helps to keep the heat in the house but I don’t think it would help with the initial heating in the morning. What can I do so it doesn’t take this long to heat up?

Comments

  • Paul Pollets
    Paul Pollets Member Posts: 3,388
    When you invest in insulation and good windows, the heat loss from the home is greatly reduced, and the home warms faster and stays warmer. When you don't, it doesn't. And it's not the boiler or radiators fault.
    rick in Alaska
  • jacobsond
    jacobsond Member Posts: 79
    Deep setback and shorter time to recover just does not work with hot water system. As long as the water is getting up to the 170 not much to do except. Set the temp and forget. Maybe a 3 degree setback for comfort while sleeping. Your not saving any money with a 10deg setback.
    coming to you from warm and sunny ND
    kcoppDZoroIronmandelta T
  • SuperJ
    SuperJ Member Posts: 605
    edited December 2018
    Don't such a large night setback. I don't like using a larger setback than I can recover from in about 45 minutes. Usually it's just a couple degrees.
    Does the boiler comes up to 170 and cycle while it heats up the house, or does it run continuously at a lower temp for the 3 hours? There are control strategies (Tekmar 263 has this, boost or indoor temp response) to automatically run your boiler a little hotter to catch up if the space is well below set point, then run cooler for better efficiency to maintain the space temp.
  • Jamie Hall
    Jamie Hall Member Posts: 15,748
    That deep a setback with a reasonably sized heating system is just asking for long runs. As @jacobsond said, limit your setback to 3 degrees and save money and be happy.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    DZoro
  • mikeg2015
    mikeg2015 Member Posts: 1,181
    Too large of a setback for forced air or hot water. I don;t care what "experts" on energy efficiency claim. To be able to recover that fast, you need oversized equipment. Oversizing reduces overall efifeinacy and comfort. Depending on outside temperature you're probably still oversized a little if the boiler is cycling on and off. 2F per hour is considered acceptabel. At design temp, it should take 12 hours to gain 10F.

    What temperature is the boiler getting to? What is the return water temperature?

    What make and model, type of boiler is it?

    You could set it to 180F if you want to heat up faster. You'll give up maybe 0.5-1% efficiency.

    Air leaks are more important than insulation.

    SuperJmichael123
  • michael123
    michael123 Member Posts: 5
    So you are saying to leave the boiler on at all times? Set the thermostat to a lower temperature so it can cycle on and off.
  • Jamie Hall
    Jamie Hall Member Posts: 15,748
    Set the thermostat to a temperature you like -- after all, heating is all about being comfortable -- and use no more than a 3 degree setback if you like it cooler at night. Let the thermostat do its thing and the boiler controls do their thing.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    DZoroIronmanCanucker1Matthias
  • Gordy
    Gordy Member Posts: 9,531
    edited December 2018
    As others have said you are using to deep of a setback.

    How long does it take to drop from 72 to 62? That’s a lot to lose overnight, or during the day.

    If you are insistent on using such a large set back then try using a learning thermostat that will anticipate how long it takes to recover, and start the recovery sooner so you are at the setting you like when you get up.

    In the end you would be better off using a smaller set back, or none at all unless that’s what temp you like for sleeping, or while away from home.

    The only way you can diminish that 3 hours is more emitter, or more insulation. The boiler probably has the btus just can’t get rid of them because the emitters are not big enough for a fast, and large recovery.

    Insulation is your best dollars spent. One you won’t lose 10 degrees. Two it will reduce the heat loss, and three it will save your fuel bill.
  • hot_rod
    hot_rod Member Posts: 14,758
    does the boiler run non stop during that period? if it cycles off and on, you may not have enough flow or radiation to move all the boiler output.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • kcopp
    kcopp Member Posts: 3,705
    Curious as to the boiler that was installed? If it has an outdoor rest curve built into it that may be exacerbating the issue.
    Got a pix? Please?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 8,863
    So it take 3 hours to warm up. What is the temperature outside with this 3 hour warm up?.

    Do you know how the contractor came up with this size boiler? Did he do a heat loss of your home?

    You are using to deep of a setback, especially in cold weather. I would not go more than 4-5 degrees. It will cost you more in fuel to raise the temp every morning
  • Voyager
    Voyager Member Posts: 262
    As others have said, insulation is your friend. It will not only lower your fuel bill, but will also allow faster heat up. If your boiler is putting out 75,000 BTUH, but your house is losing 70,000 to the outdoors, that leaves only 5,000 to raise the temp in the house. If you install insulation and reduce the heat loss to 60,000, a 14% reduction in heat loss, that now leaves 15,000 BTUH available to raise the temp in your home which is now 3 times more than originally. This will greatly reduce the time required to raise the temp in your home.

    And, as has also been said, hot water heat generally isn’t the most responsive. You can get away with 10 degrees of setback with a fast responding forced air system, but you are likely better off with 5 degrees or so with hot water heat. You won’t save as much money as with the deeper setback, but you will be a lot more comfortable taking your shower in the morning. 🥶
  • Gordy
    Gordy Member Posts: 9,531
    edited December 2018
    I’m also with @hot rod_7 . It’s a little cloudy if boiler is reaching 170, And cycling, or not getting to 170, and doesn’t shut down for the 3 hours. By cycling we mean there is still a call for heat, but the burner shuts off, and the pump still runs because high limit of 170 is reached, and then relights once the lower differential is hit.
  • Voyager
    Voyager Member Posts: 262
    Gordy said:

    The only reason you get away with fast farced air recovery is that it warms the air which is what the thermostat senses. The mass is still greatly lagging that setpoint. Which leads to comfort distress.

    I disagree. I have a house heated by forced air and a large workshop heated by in-slab hydronic. Both are comfortable, but have quite different characteristics. However, when it comes to handling setbacks, it is forced air all the way. I set my home back to 64 at night and have the thermostat sent to go back to 72 10 minutes before my alarm goes off. Most days the warmth wakes me before the alarm goes off. And by the time I am out of the shower, the house is at 72. You won’t do that with hydronics. And most of the mass inside the house (furniture, etc.) cools more slowly than the air during the night so it doesn’t need to warm up the full 8 degrees, maybe 4 degrees. The house is very comfortable 20 minutes after the heat comes on.

    I know it is popular for many old hydronics folks to rag on forced air and use pejorative terms like scorched air or farced air as you favor, but that simply shows your lack of understanding of the capabilities of a modern, well-designed forced air system. I like all types of heating systems, steam radiators to modern forced air, but each has its pros and cons and none is perfect. And I don’t subscribe to bashing any type of heating system as all have their place depending on the attributes of interest to the end user.
  • Voyager
    Voyager Member Posts: 262
    Gordy said:

    Well we will agree to disagree then. I have lived with both in a living environment not a shop. Big difference. I speak purely from a radiant stand point. The mass will never keep pace with the hot air satisfying the thermostat.

    I have no problem agreeing to disagree. I have also lived and worked with both for more than 40 years. Most of the time was with poorly designed forced air systems in mobile homes (my early years) and poorly built homes later on. I really disliked forced air by the time I build my house 19 years ago.

    When I designed and built my log home, my plan was hot water baseboard. However, I wanted AC, air filtration, outside air exchange and possibly humidification. The first HVAC company I hired was a bust and I had to fire him midstream. Due to time constraints and other trades being held up, I had to quickly get a replacement and ended up hiring a company that does mostly commercial and very large residential work. Their designer convinced me that a well-designed forced air system was the best way to address all of my desires. We discussed the noise and draft issues and he convinced me that those were due to poor design. Even though I had reservations, I agreed to his design.

    He was correct. My system is quiet, has no drafts (unless you sit on top of a register) and heats evenly and quickly. And the AC is equally effective as are the HRVs, all using common ductwork. The key is lots of registers and low flow velocity. I think the “great room” in my house has 6 registers as the two prow walls are mostly windows. I can sit in front of the glass on a 0 degree night and be completely comfortable.

    I am happy we can disagree respectfully and I will continue to advocate for a range of systems, including forced air, depending on what the user needs and wants from their system. If they really want 8-10 degree nightly setbacks to get their preferred sleeping temps (I like it below 65 at night) yet need fast recovery to get ready for work in the morning, forced air is the only economical way I know of to do this. Steam comes close, but only when the radiators are dangerously hot.

    Every system type comes with attributes and compromises. I think users need to hear all the details about all the system types so that they can make the best decision for their needs. There simply is, in my opinion, no one best system for all applications.
  • captainco
    captainco Member Posts: 465
    As far as savings it is recommended that a setback of more than 5 degrees for 8 hours is the maximum. 16 hours or more a 10 degree setback is okay as far as savings. ASHRAE did a study in the 80's that stated equipment needs to be oversized to recover from setback quickly, This did apply to furnaces but as far as boilers are concerned there will be a comfort issue regardless.
  • Voyager
    Voyager Member Posts: 262
    captainco said:

    As far as savings it is recommended that a setback of more than 5 degrees for 8 hours is the maximum. 16 hours or more a 10 degree setback is okay as far as savings. ASHRAE did a study in the 80's that stated equipment needs to be oversized to recover from setback quickly, This did apply to furnaces but as far as boilers are concerned there will be a comfort issue regardless.

    Yes, I am sure that my furnaces are oversized by currently accepted design rules, but efficiency loss is not great with a furnace as the thermal mass of the air to air heat exchanger is small. I use setback primarily for comfort rather than fuel savings. I like it in the 70-72 range during the day, unless I am doing some strenuous activity. However, that temp at night is way too warm for comfortable sleeping for me. I like it 65 or below and use 64 as a good compromise as that allows a fairly quick recovery in the morning.

    If I had hot water heat, I would likely have to keep it at 68 all of the time which means I would be too chilly during the day and too warm at night. Or maybe do a very small setback using say 70 during the day and 66 and night with the recovery starting a couple of hours before alarm time.

    My workshop has radiant slab heat which is fantastic most of the time, unless you have a wide temperature swing. It then grossly overshoots during the day. I keep it at 55 so the overshoots to 58 aren’t a big deal, however, in the spring if it overshoots to 65 or 70, which could happen with some of our 40 degree night to day temp swings in PA, I will have to open windows to work comfortably.
  • Gordy
    Gordy Member Posts: 9,531
    captainco said:

    As far as savings it is recommended that a setback of more than 5 degrees for 8 hours is the maximum. 16 hours or more a 10 degree setback is okay as far as savings. ASHRAE did a study in the 80's that stated equipment needs to be oversized to recover from setback quickly, This did apply to furnaces but as far as boilers are concerned there will be a comfort issue regardless.

    Of course that was the carter administration era. When thermostats went to 65. an estimated reduction of 330,000 barrels of oil a day. Must have been a lot of oil fired equipment back then.........

  • Voyager
    Voyager Member Posts: 262
    Gordy said:

    captainco said:

    As far as savings it is recommended that a setback of more than 5 degrees for 8 hours is the maximum. 16 hours or more a 10 degree setback is okay as far as savings. ASHRAE did a study in the 80's that stated equipment needs to be oversized to recover from setback quickly, This did apply to furnaces but as far as boilers are concerned there will be a comfort issue regardless.

    Of course that was the carter administration era. When thermostats went to 65. an estimated reduction of 330,000 barrels of oil a day. Must have been a lot of oil fired equipment back then.........

    Wasn’t it Carter who banned use of natural gas for electricity generation back in 1978? That certainly didn’t help in reduction of petroleum use.
  • DZoro
    DZoro Member Posts: 1,049
    Lower your slab water temperature. Will help with heat bill and overshoots. Slab sensor would help with both also.
  • Voyager
    Voyager Member Posts: 262
    DZoro said:

    Lower your slab water temperature. Will help with heat bill and overshoots. Slab sensor would help with both also.

    SWT is only 80 now. The overshoots are a result of physics, not lack of control. The control is good at steady state, but when it is 20 all night and then hits 40 the next day, you can’t keep the heat from coming out of the slab. It is just the nature of the beast.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,665
    Lower your slab water temperature. Will help with heat bill and overshoots. Slab sensor would help with both also.


    I have the reset curves for my system so tight that I cannot practically do setbacks at all.

    One zone is radiant slab at grade, and when it is warm outside (50F or greater), if there is a call for heat, supply is 80F. If it goes to 0F outside, supply is 130F. Design temperature is 14F around here. Before I thought about it, I tried a setback of something like 5F. Well, if I started the setback at 4PM, my radiant zone had not dropped 5F by the next morning. I have no idea anymore how long it would take to recover from that setback. I do not see how a slab sensor would help with something like this. The thermal mass of the slab is just too great. If I want to change the inside temperature by a degree or too, it takes well over 24 hours to stabilize the system after the change.

    The other zone is fin-tubed baseboard. Oversize. When I had the mod-con put in, I replaced the old 3 foot long baseboards with 14 foot long ones. Supply goes from 120F to 150F, depending on outside temperature. My mod-con has very flexible control board. I have separate reset curves for each zone, and on the baseboard zone, I tell it that if it has not recovered from the setback in two hours, to up the supply temperature by 10F, and after another two hours, if it has not recovered, to up the supply by another 10F (but never go above 150F). Overnight, that zone can drop 4F from setback, but it takes a lot more than four hours to recover, even with the boosted reset curves. So the simplest digital thermostats would do me just fine.
  • Ironman
    Ironman Member Posts: 6,359
    @Voyager ,
    You need outdoor reset controlling the SWT to the slab. When properly setup, the thermostat will just be a high limit control.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    DZoroGordy
  • Voyager
    Voyager Member Posts: 262
    edited December 2018
    Ironman said:

    @Voyager ,
    You need outdoor reset controlling the SWT to the slab. When properly setup, the thermostat will just be a high limit control.

    ODR is in use and the curve is programmed for 0/110 to 65/70.
  • Gordy
    Gordy Member Posts: 9,531
    If there are huge daily outdoor temp swings with any type of high mass heating system you will have issues with controlling over shoot with a poor control strategy.

    With out Outdoor reset, and slab sensors controlling the supply temp to the emitters it’s a bang bang control strategy.






  • DZoro
    DZoro Member Posts: 1,049
    Lower your warmest day temp (110). It's sort of misleading the way they ask it. What they really want is at what outdoor temp would you not want much/no heat input to the home. So my thoughts on this is that if the outdoor temp is above my indoor comfort level temp ,then I wish not to have the system on. Suggest 70* outdoor instead of 110*. This will change the large swings with your slab.
    Curious what boiler do you have? Is it the Triangle Tube with 2 different temperature settings ?
    Are you also controlling your radiators with odr?
  • Ironman
    Ironman Member Posts: 6,359
    Voyager said:

    Ironman said:

    @Voyager ,
    You need outdoor reset controlling the SWT to the slab. When properly setup, the thermostat will just be a high limit control.

    ODR is in use and the curve is programmed for 0/70 to 65/110.
    Are you saying that at 0* outside, the target is 70* SWT, and at 65*, the target is110*??

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Gordy
    Gordy Member Posts: 9,531
    edited December 2018
    I like to think of Warm weather shut down as the temp where the structure needs no heat input from the source, and not what you are looking for in setpoint. A house can be different than a shop due to insulation,solar, and internal gains. 65 can be way to high.

    If you keep the shop at 58 then adjust WWS accordingly.
  • Zman
    Zman Member Posts: 6,540
    @Voyager , you totally hijacked this thread making it difficult to answer the OP's question. It is way better to start another thread in cases like this.

    @michael123 , It sounds like your system is running normally. If you like deep setbacks for comfort, you might need to set your t-stats to start changing temp earlier.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    DZoro
  • Voyager
    Voyager Member Posts: 262
    Zman said:

    @Voyager , you totally hijacked this thread making it difficult to answer the OP's question. It is way better to start another thread in cases like this.

    @michael123 , It sounds like your system is running normally. If you like deep setbacks for comfort, you might need to set your t-stats to start changing temp earlier.

    No intent to hijack, just trying to help the OP understand that with high mass emitters you are going to have slow response due simply to the physics involved. Cast iron radiators aren’t the highest mass systems around, but they are higher mass than fin tube emitters and much higher mass than forced air systems. And you are dealing with heat transfer due to radiation which is fast, but only partial, and also significantly to natural convection. Natural convection is very slow compared to forced convection.

    Deep setbacks require a very responsive heating system. This typically means forced air in a residential application. You can also use very hot radiant in commercial settings such as the gas fired tubes in some big box warehouse stores, but you need them nearly red hot to radiate enough heat to warm things quickly.

    So, I think the OPs question was answered thoroughly. Use less aggressive setbacks and/or use a thermostat that either will learn to come out of setback earlier or that can be programmed to start warming up earlier.
  • Gordy
    Gordy Member Posts: 9,531
    Not entirely.
    I'd still like to know if boiler is cycling, and reaching high limit, or running the full three hours, and not hitting high limit.

    Also what the boiler package is. Ci, or mod/con. Reset, or not.

    A boiler cycling, and taking a long time to reach set point is a different scenario than a boiler running flat out, and never reaching high limit.
    IronmanDZoro
  • Zman
    Zman Member Posts: 6,540
    The conversation regarding setbacks and whether you are heating the air or the mass is an interesting one.

    It all comes back to the idea of "cold 70 vs warm 70". When you heat the air quickly, whether it is with forced air or radiators, it takes some time for the mass of the structure to catch up. When the mass of the building is cold and the air is warm, thermal comfort is sacrificed. I comes down to the mean radiant temp of the surfaces as compared to the air temp.

    It should be noted that this is very subjective. What is comfortable for one person is can be drastically different for another.

    This gives a good overview. https://en.wikipedia.org/wiki/Thermal_comfort
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Voyager
    Voyager Member Posts: 262
    Ironman said:

    Voyager said:

    Ironman said:

    @Voyager ,
    You need outdoor reset controlling the SWT to the slab. When properly setup, the thermostat will just be a high limit control.

    ODR is in use and the curve is programmed for 0/70 to 65/110.
    Are you saying that at 0* outside, the target is 70* SWT, and at 65*, the target is110*??

    My mistake. I wrote it backwards. 110 boiler temp at 0 outside. 70 boiler temp at 65 outside. I can still go lower as the TT cc50S will allow the low temp to be 60 and the high to be 86 so I still have room to experiment.
    kcopp
  • Ironman
    Ironman Member Posts: 6,359
    What's your tubing size, spacing and length? 110* SWT seems high for a shop.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Zman
    Zman Member Posts: 6,540
    Voyager said:

    Ironman said:

    Voyager said:

    Ironman said:

    @Voyager ,
    You need outdoor reset controlling the SWT to the slab. When properly setup, the thermostat will just be a high limit control.

    ODR is in use and the curve is programmed for 0/70 to 65/110.
    Are you saying that at 0* outside, the target is 70* SWT, and at 65*, the target is110*??

    My mistake. I wrote it backwards. 110 boiler temp at 0 outside. 70 boiler temp at 65 outside. I can still go lower as the TT cc50S will allow the low temp to be 60 and the high to be 86 so I still have room to experiment.
    Ironman said:

    What's your tubing size, spacing and length? 110* SWT seems high for a shop.

    Completely different conversation.....
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Voyager
    Voyager Member Posts: 262
    Ironman said:

    What's your tubing size, spacing and length? 110* SWT seems high for a shop.

    I don’t want to keep this off-topic thread doing, but I don’t now how to create a new thread from your message. I guess I can copy your message and paste it in as the start of a new thread and continue there.
    kcoppDZoro
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