ᐅ Heating screed with a heating device versus a heat pump – costs?
Created on: 14 Sep 2022 22:04
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Sandra.M85
Hello,
Two weeks ago, the screed (cement screed) was poured in our new single-family home (about 130 sqm (1400 sq ft) floor area).
Our general contractor (GC) now offers us the following options:
1) Heating the screed using a 19 kW heating device, starting in 10 days.
2) Heating the screed via underfloor heating powered by a heat pump after the heat pump is installed in mid-October.
According to our contract, I am responsible for paying the heating costs, while the GC covers construction electricity. The house completion date is set for February 2023 in the contract.
Option 1: The GC says I must pay for the construction electricity used by the heating device because it counts as heating costs. Until now, I assumed that heating costs cover the energy needed to keep the workers working, but not the energy used specifically to heat the screed. If I prefer option 1, I understand that I will have to cover these costs, but the GC will still complete the house by February using the cheaper option 2.
How expensive would option 1 be? What is the cost of construction electricity, and how much electricity is needed to operate the heating device until the screed is dry?
According to the GC, option 1 would allow me to move in this year, which could save me about one month’s rent for my current apartment—around 650 euros—and avoid the risk that the heat pump might not be installed by mid-October, as required for option 2.
Option 2: After the heat pump is installed in mid-October, if the screed is heated via underfloor heating, does the GC cover the electricity used for this? Would this electricity still be measured by the construction electricity meter (paid by the GC according to the contract), or would it already be charged through my new private electricity meter?
How much electricity would be needed to heat the screed this way, and if I had to pay for this electricity, approximately how much cheaper would option 2 be compared to option 1?
Which option would you choose?
Two weeks ago, the screed (cement screed) was poured in our new single-family home (about 130 sqm (1400 sq ft) floor area).
Our general contractor (GC) now offers us the following options:
1) Heating the screed using a 19 kW heating device, starting in 10 days.
2) Heating the screed via underfloor heating powered by a heat pump after the heat pump is installed in mid-October.
According to our contract, I am responsible for paying the heating costs, while the GC covers construction electricity. The house completion date is set for February 2023 in the contract.
Option 1: The GC says I must pay for the construction electricity used by the heating device because it counts as heating costs. Until now, I assumed that heating costs cover the energy needed to keep the workers working, but not the energy used specifically to heat the screed. If I prefer option 1, I understand that I will have to cover these costs, but the GC will still complete the house by February using the cheaper option 2.
How expensive would option 1 be? What is the cost of construction electricity, and how much electricity is needed to operate the heating device until the screed is dry?
According to the GC, option 1 would allow me to move in this year, which could save me about one month’s rent for my current apartment—around 650 euros—and avoid the risk that the heat pump might not be installed by mid-October, as required for option 2.
Option 2: After the heat pump is installed in mid-October, if the screed is heated via underfloor heating, does the GC cover the electricity used for this? Would this electricity still be measured by the construction electricity meter (paid by the GC according to the contract), or would it already be charged through my new private electricity meter?
How much electricity would be needed to heat the screed this way, and if I had to pay for this electricity, approximately how much cheaper would option 2 be compared to option 1?
Which option would you choose?
May I join the discussion for a moment?
Many points raised so far have been correct, but some comments were rather questionable and/or inaccurate.
It is true that the functional heating is used to test all components involved in the installation of a warm water underfloor heating system.
Since the screed at this stage is still "untouched," meaning it still contains a significant amount of water that can cause considerable internal stresses during drying/heating, which have not yet been released, this phase must be done gradually, in several stepped temperature stages.
So far, so good.
However, regarding the final drying heating phase, it is not, as "SaniererNRW123" stated, necessary to maintain the maximum temperature for 21 days!
The term "21 days" in DIN EN 1264-4, section 4.2.4, refers exclusively to the waiting period after the installation of a cement screed before it should be heated.
This standard does not provide any indication about the duration of the maximum heating phase during the final drying heating.
No standard or guideline can do this because drying conditions depend on the specific object, the nominal screed thickness, and the type of binder, which all influence the drying speed.
For example, if I tightly close all windows and have an 80mm (3 inches) thick screed, I could theoretically keep heating indefinitely without the screed reaching final dryness.
Here, it should be briefly noted that the CM residual moisture measurement carried out by the floor installer is crucial to determine whether the heating phase (usually a maximum of 3 days) was sufficient or if heating (and of course ventilation) must continue.
Regarding the question: does the supply temperature have to be 50°C (122°F) if I later use a heat pump with a supply temperature of 30°C (86°F)?
Unfortunately, the answer is: YES AND NO.
Why?
Calcium sulfate screeds must not be heated above 40°C (104°F) at the heating elements. Therefore, the 50°C limit does not apply to this binder.
For cement screeds, the maximum temperature should be set after functional heating and approximately 3 days of rest at room temperature, which the heating system is able to provide!
The final drying heating is exclusively intended to drive out excess mixing water and has nothing to do with the later use (low-temperature heating)!
This should clarify the questions on this topic.
Best regards and good luck: KlaRa
Many points raised so far have been correct, but some comments were rather questionable and/or inaccurate.
It is true that the functional heating is used to test all components involved in the installation of a warm water underfloor heating system.
Since the screed at this stage is still "untouched," meaning it still contains a significant amount of water that can cause considerable internal stresses during drying/heating, which have not yet been released, this phase must be done gradually, in several stepped temperature stages.
So far, so good.
However, regarding the final drying heating phase, it is not, as "SaniererNRW123" stated, necessary to maintain the maximum temperature for 21 days!
The term "21 days" in DIN EN 1264-4, section 4.2.4, refers exclusively to the waiting period after the installation of a cement screed before it should be heated.
This standard does not provide any indication about the duration of the maximum heating phase during the final drying heating.
No standard or guideline can do this because drying conditions depend on the specific object, the nominal screed thickness, and the type of binder, which all influence the drying speed.
For example, if I tightly close all windows and have an 80mm (3 inches) thick screed, I could theoretically keep heating indefinitely without the screed reaching final dryness.
Here, it should be briefly noted that the CM residual moisture measurement carried out by the floor installer is crucial to determine whether the heating phase (usually a maximum of 3 days) was sufficient or if heating (and of course ventilation) must continue.
Regarding the question: does the supply temperature have to be 50°C (122°F) if I later use a heat pump with a supply temperature of 30°C (86°F)?
Unfortunately, the answer is: YES AND NO.
Why?
Calcium sulfate screeds must not be heated above 40°C (104°F) at the heating elements. Therefore, the 50°C limit does not apply to this binder.
For cement screeds, the maximum temperature should be set after functional heating and approximately 3 days of rest at room temperature, which the heating system is able to provide!
The final drying heating is exclusively intended to drive out excess mixing water and has nothing to do with the later use (low-temperature heating)!
This should clarify the questions on this topic.
Best regards and good luck: KlaRa
S
SaniererNRW12316 Sep 2022 09:49KlaRa schrieb:
Calcium sulfate screeds must not be heated above 40°C (104°F) on the heating elements. The 50°C (122°F) limit does not apply to this binder under any circumstances. Just out of interest: Where is that stated?
The reason I ask is that every heating protocol I know of sets the limit at 50 degrees Celsius (122°F), regardless of whether it’s from screed layers or screed manufacturers.
KlaRa schrieb:
For cement screeds, the maximum temperature after functional heating and about three days of waiting at room temperature should be set to whatever the heating system is capable of delivering! I would also like to question this statement. Why should I heat up to 65°C (149°F), which many heat pumps can achieve, to reach screed maturity (you mentioned after the functional heating)? To my knowledge, 55°C (131°F) is the maximum temperature that should be used.
KlaRa schrieb:
Regarding screed maturity heating, it is not the case, as "SaniererNRW123" noted, that the maximum temperature must be maintained for 21 days! Please quote my source correctly. I did not say "must," but "generally." As a rule of thumb, or according to most screed heating protocols, about three weeks is the usual timeframe.
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xMisterDx28 Sep 2022 14:23Does anyone know the design flow temperature for the heating system? Saying it only needs to be heated up to 30°C (86°F) doesn’t really make sense. A heat pump can also be designed for a flow temperature of 35 or 40°C (95 or 104°F).
Especially when drying the screed, I would prefer to run functional heating at 40°C (104°F) rather than 30°C (86°F)... otherwise, you might end up waiting several extra weeks for the moisture measurement to be acceptable, losing time.
The rent of 650 EUR per month is probably not the only ongoing cost. Consider the loan (interest on the drawn amount without repayment, possibly commitment fees). Plus, you will need to heat two apartments/houses this winter, which is likely not included in the 650 EUR.
By the way, heating up with heat pumps is usually done (mostly) using an electric heating element due to the high power demand. So, you’re not really saving anything compared to the hot water heater. On the contrary, your heat pump will hardly have a 19 kW electric heater, so it won’t be able to reach 40°C (104°F) easily or will be heavily stressed right at the start... which heat pumps really don’t like.
Especially when drying the screed, I would prefer to run functional heating at 40°C (104°F) rather than 30°C (86°F)... otherwise, you might end up waiting several extra weeks for the moisture measurement to be acceptable, losing time.
The rent of 650 EUR per month is probably not the only ongoing cost. Consider the loan (interest on the drawn amount without repayment, possibly commitment fees). Plus, you will need to heat two apartments/houses this winter, which is likely not included in the 650 EUR.
By the way, heating up with heat pumps is usually done (mostly) using an electric heating element due to the high power demand. So, you’re not really saving anything compared to the hot water heater. On the contrary, your heat pump will hardly have a 19 kW electric heater, so it won’t be able to reach 40°C (104°F) easily or will be heavily stressed right at the start... which heat pumps really don’t like.
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xMisterDx28 Sep 2022 14:36Sandra.M85 schrieb:
Earlier, an energy demand of about 6300 kWh was mentioned for my project. Where does this large difference come from?Key question:
Is the house already insulated?
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neo-sciliar30 Sep 2022 10:09Wow, the initial question was whether to heat using an external heater or a heat pump. Then it shifted to “How should the screed be heated?”
So: You can have a long discussion about heating the screed, but the requirements come from the screed installer, and if you want to keep the warranty, you need to follow their guidelines as documented.
Yes, an external heater uses significantly more electricity than a heat pump. This depends on the heat pump’s seasonal performance factor, which traditionally tends to be lower at high temperatures. So, roughly half the electricity the heat pump consumes. This difference is often offset just by the rental cost for the external heater over a month.
Please also consider: the amount of heat required is roughly equivalent to the home’s annual heating demand. That means your heat pump is basically running at full load for an entire year when it’s commissioned for the house. This is a strong argument in favor of the external heater.
So: Option 1.
So: You can have a long discussion about heating the screed, but the requirements come from the screed installer, and if you want to keep the warranty, you need to follow their guidelines as documented.
Yes, an external heater uses significantly more electricity than a heat pump. This depends on the heat pump’s seasonal performance factor, which traditionally tends to be lower at high temperatures. So, roughly half the electricity the heat pump consumes. This difference is often offset just by the rental cost for the external heater over a month.
Please also consider: the amount of heat required is roughly equivalent to the home’s annual heating demand. That means your heat pump is basically running at full load for an entire year when it’s commissioned for the house. This is a strong argument in favor of the external heater.
So: Option 1.
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xMisterDx1 Oct 2022 14:20I spoke with my installer yesterday. He said that with a heat pump, we can’t expect delivery this winter. He’s still getting small amounts of gas heaters, but probably none available for me this year either.
So definitely option 1 if the house is to be finished by spring.
So definitely option 1 if the house is to be finished by spring.
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