How much heat?

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powerplay

Senior Member
In an enclosed patio, with many double pane vinyl windows and insulated walls the heat loss is pretty high. The square feet dictates an 1250 watt baseboard heater. The owner only wants a small heater that will prevent the water lines on a washing machine from freezing. My question is if an 500 watt heater is used and on all the time, with an 1250 watt heater cycling on and off and properly heating the area, would there be a huge difference in heating cost?.... tough question because we are supposed to provide the right calculated heater, but the customer gets what they want if it's safe...?
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
The owner only wants a small heater that will prevent the water lines on a washing machine from freezing. My question is if an 500 watt heater is used and on all the time, with an 1250 watt heater cycling on and off and properly heating the area, would there be a huge difference in heating cost?
If both heaters are controlled by a thermostat or thermostats set at the same temperature, the units of heat released by the heaters will be the same, as the units of heat lost from the enclosed patio is a function of the temperature difference from the interior to the exterior, and the construction of the envelope, not a function of the source of heat.

Bottom line, there is no substantial difference in the watt hours needed. The kWh cost will be essentially the same for either heater.

The real value of the larger wattage heating unit is it will protect the pipes against freezing also when the rare deep cold snap occurs. That's a definite safety factor.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I would venture a guess that the 500 watt will keep it from freezing but will run constantly at times since most thermostats will not go below 50 degrees. Locate the heater close to the water lines.
 

powerplay

Senior Member
Excellent! ...that's what i had hoped to hear! Many times the customer simply wants a value, and the difference in the cost of the heaters isn't a big deal, and I feel better doing the right thing...thanks for all the feedback...love this site!
 

powerplay

Senior Member
Are there any safety issues from using an undersized heater in an enclosed patio running non-stop in cold snaps? Usually if they're properly sized they would cycle, but if the owner does not want to heat the patio and simply prevent pipe freezing, any problems anyone can think of?
 
In an enclosed patio, with many double pane vinyl windows and insulated walls the heat loss is pretty high. The square feet dictates an 1250 watt baseboard heater. The owner only wants a small heater that will prevent the water lines on a washing machine from freezing. My question is if an 500 watt heater is used and on all the time, with an 1250 watt heater cycling on and off and properly heating the area, would there be a huge difference in heating cost?.... tough question because we are supposed to provide the right calculated heater, but the customer gets what they want if it's safe...?

So put electric self limiting heat tracing cable and insulate the water pipe up to the first solenoid valve. 2W/ft. Have an ambient thermostat switch the power onto it @ 40F. Easy-peasy....
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Bottom line, there is no substantial difference in the watt hours needed. The kWh cost will be essentially the same for either heater.
That would be dependent upon the temperature at which you set the thermostats.
Set both stats at 70? and both heaters may run 24/7 to try and attain 70?. In that case the larger heater will cost plenty more to run.
 

iwire

Moderator
Staff member
Location
Massachusetts
So put electric self limiting heat tracing cable and insulate the water pipe up to the first solenoid valve. 2W/ft. Have an ambient thermostat switch the power onto it @ 40F. Easy-peasy....

Yeah, I guess the customer will not mind the remaining water in the washer freezing up and splinting things.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
That would be dependent upon the temperature at which you set the thermostats.
Set both stats at 70? and both heaters may run 24/7 to try and attain 70?. In that case the larger heater will cost plenty more to run.
:confused: Well, yeah, if you take my sentence as a universal generalization outside of the context of the OP.

I start from the assumption that the OP did the correct calculations for that job's location and that both heaters satisfy the described use.

The little heater is large enough to keep the room at a design temp above freezing, and the large heater is large enough to meet that design temp of the square foot heat calculation method referred to.

Then, as I said in my first post, :
If both heaters are controlled by a thermostat or thermostats set at the same temperature
then the context is established. I should have gone on to say the lower (non-freeze) temperature should be used.

Looking at ways one heater can use more energy than the other is looking at the wrong point. May be interesting. But the important concept is the heat flow through the thermal resistance of the envelope of the heated volume, IMO. At a fixed interior temp, the design temp, the heat flow through the thermal resistance of the volume's envelope is the same, regardless of the source of the heat.
 
Yeah, I guess the customer will not mind the remaining water in the washer freezing up and splinting things.

The variety of washer constructions are infinite so you can't say for sure that there would be water left and it is not self draining after the cycle is finished. (I know mine is.)

But lets say it is true, it would still be less costly and more energy efficient to heat trace and insulate ALL PARTS THAT may contain residual water - OP to check with Iwire, our resident washing-machine guru - than heat the entire room.
 

mikeames

Senior Member
Location
Germantown MD
Occupation
Teacher - Master Electrician - 2017 NEC
I would agree with the above. If the customer is only worried about freeze up why not heat tape? The majority of washers have plastic drain pipes and pans which can sustain the expansion of the small amount of water left if any should freeze.

If they really want to heat it any bit for comfort than IMHO the 500 watt heater will be a spit in the bucket.
 

iwire

Moderator
Staff member
Location
Massachusetts
The variety of washer constructions are infinite so you can't say for sure that there would be water left and it is not self draining after the cycle is finished. (I know mine is.)

But lets say it is true, it would still be less costly and more energy efficient to heat trace and insulate ALL PARTS THAT may contain residual water - OP to check with Iwire, our resident washing-machine guru - than heat the entire room.

Guru? No. But I have moved and worked on many washers and all have contained a fair amount of water when not in use.

But you are right, it is much better to assume it will not be a problem.


The majority of washers have plastic drain pipes and pans which can sustain the expansion of the small amount of water left if any should freeze.

Again, I was mistaken, it is better to guess the mans washer can tolerate freeze ups. :grin:

The 'correct' answer may be to place the Washer in a better location.
 

__dan

Senior Member
mountain people

mountain people

I have the cost of the 500 watt baseboard heater running 7/24 for one month at $43.20. So the homeowner may be correct, the cost of defrosting the washer is less than the cost of running out with the laundry. The savings come from maintaining space temp at a lower temperature or by the arrangement, localizing the heat close to where you need it.

If the patio room is on piers and the cold air blows under the floor, it will be a lot harder to heat. If he is on a slab or crawl space foundation, the below grade foundation gives a lot of stability to maintain space temp.

If you only want to defrost the washer and nothing else, place the baseboard heater behind the washer, between the washer and the wall. You will have a higher probability of intercepting the heat before it gets outside and the steel washer skin will warm up and conduct / radiate in the area where the heat is necessary.

Moving the washer would be the conventional solution.
 

kwired

Electron manager
Location
NE Nebraska
The variety of washer constructions are infinite so you can't say for sure that there would be water left and it is not self draining after the cycle is finished. (I know mine is.)

But lets say it is true, it would still be less costly and more energy efficient to heat trace and insulate ALL PARTS THAT may contain residual water - OP to check with Iwire, our resident washing-machine guru - than heat the entire room.

I have not seen a washer that will expel all of the water from inside. Once the pump is dry what ever water is beyond the pump but has not been pushed to the drain will flow back into the pump once it stops running. If left in freezing temperature will crack the pump housing.
 
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