Cheap Heat electric add-on

Hi Lady Fitz,

Thanks for the link. I'll read it carefully.

22 amps @ 240 volts--but I believe (or I hope) it is balanced between the 2 120 volt "legs". So wattage is 5280 and btu's are 18016 giving a total daily maximum output with no voltage drop of 432384 btu's.

I see the 50 amp ones are balanced--but the biggest is only 21.6 amps

That means a few less watts and a few less btu's

21.6 @ 120 x 2 = 5184 watts = 17688 x 24 = 424512 btu's per day with zero voltage drop.

I'm not terribly familiar with voltage drop on 50 amp units. Is it an issue from time to time?

Ok, I can accept those figures (I never believed the smallest unit would ever be adequate; I just wanted to see if you could actually back it up with something more solid than your opinions); there are a few points, though:

The largest unit draws only 22A (at 240v).

Propane furnaces normally cycle on and off. Cheap Heat can run full time so it usually can put out the same amount of heat as a lager rated gas furnace. Of course, we don't know if that furnace ran full time or not during the night. We also don't know the ambient temperatures.

Aqain, all one would need would be a two stage thermostat (and, if the thermostat leaves the first stage on when it switches to the second stage, a relay) to allow the furnace to switch from electric to propane when and if the temperature drops too low for the Cheap Heat to keep up with.

I stand corrected on the location.

While I'm at it, Trailer Life recently had an article on the Cheap Heat. You all can read it here.

pianotuna wrote:
Hi Lady Fitzgerald.

Please read more carefully. The folks who were visiting were from Tx. The Montana is in KY.

Here are the numbers:

He was running 3000 watts of heaters that's 10236 btu's. He went through 45 pounds of propane, but we don't know the time frame other than it was Thanksgiving. Let's guess it was a week?

Propane does 21499 btu's per pound. Lets say his furnace was only 70% efficient? (it is probably 80). 21499 X 0.7 =~ 15000 btu's (rounding down for worst case?)

15000 x 45 = 675000 btu's

675000 / 7 days = 96428 btu's per day from the furnace.

10236 x 24 = 245664 btu's from the two electric heaters

So his heat requirements are 342092 btu's per day.

The smallest cheap heat is 16 amps or about 1920 watts which is 6551 btu, assuming zero voltage drop.

6551 x 24 = 157224

That means the smallest cheap heat is in a deficit position and can't possibly work. But that is no surprize.

The largest cheap heat is 42 amps or about 5040 watts. That works out to 17197 btu's

17197 x 24 = 412728 btu's

This is more than enough and the unit would cycle on and off.

The medium If I remember correctly (they have removed the web page, so I can't go back and check) is 32 amps

32 x 120 = 3840 watts or 13102 btu's (again with zero voltage drop)

13102 x 24 = 314448 btu's. So it might not be enough at night.

Also I maximized the possible output of the cheap heat and minimized the propane furnace. If I redid it with the propane at 80% efficiency and a voltage drop of 10% the medium size probably won't "cut the mustard". Certainly it would be constantly be on during the night, if not 24 hours. Since by design the cheap heat is "either or" the propane furnace would have to carry the entire load at night when the temperatures are the lowest. Too sad, too bad.

If the visit were only 4 days then even the largest 42 amp unit would be being pushed to its limits.

We also don't know if it was 45 lbs of propane--it might be more--or it might be less.

I hope I did not make any errors. This is a "back of an envelope" calculation, so only one step up from a "guess".

I'm sure you have more expertize than I do in this area lady fitz. Please knock the stuffing out of this email so I can learn from you.

Good calculating Pianotuna. thanks for taking the time to do this.

Hi Lady Fitzgerald.

Please read more carefully. The folks who were visiting were from Tx. The Montana is in KY.

Here are the numbers:

He was running 3000 watts of heaters that's 10236 btu's. He went through 45 pounds of propane, but we don't know the time frame other than it was Thanksgiving. Let's guess it was a week?

Propane does 21499 btu's per pound. Lets say his furnace was only 70% efficient? (it is probably 80). 21499 X 0.7 =~ 15000 btu's (rounding down for worst case?)

15000 x 45 = 675000 btu's

675000 / 7 days = 96428 btu's per day from the furnace.

10236 x 24 = 245664 btu's from the two electric heaters

So his heat requirements are 342092 btu's per day.

The smallest cheap heat is 16 amps or about 1920 watts which is 6551 btu, assuming zero voltage drop.

6551 x 24 = 157224

That means the smallest cheap heat is in a deficit position and can't possibly work. But that is no surprize.

The largest cheap heat is 42 amps or about 5040 watts. That works out to 17197 btu's

17197 x 24 = 412728 btu's

This is more than enough and the unit would cycle on and off.

The medium If I remember correctly (they have removed the web page, so I can't go back and check) is 32 amps

32 x 120 = 3840 watts or 13102 btu's (again with zero voltage drop)

13102 x 24 = 314448 btu's. So it might not be enough at night.

Also I maximized the possible output of the cheap heat and minimized the propane furnace. If I redid it with the propane at 80% efficiency and a voltage drop of 10% the medium size probably won't "cut the mustard". Certainly it would be constantly be on during the night, if not 24 hours. Since by design the cheap heat is "either or" the propane furnace would have to carry the entire load at night when the temperatures are the lowest. Too sad, too bad.

If the visit were only 4 days then even the largest 42 amp unit would be being pushed to its limits.

We also don't know if it was 45 lbs of propane--it might be more--or it might be less.

I hope I did not make any errors. This is a "back of an envelope" calculation, so only one step up from a "guess".

I'm sure you have more expertize than I do in this area lady fitz. Please knock the stuffing out of this email so I can learn from you.

I think the size of the unit needed will be determined by the expected temperatures you have to operate in. For example 2400 watts of heat evenly distributed throughout our 40 foot motorhome is enough to keep it comfortable in the 10 to 15 degree fahrenheit range. (say minus 5 C or so) If you don't expect to be in temps below that the smaller unit might be fine.

Re the warranty thing, although a valid concern, remember warranties are only good for a year or two anyway.

pianotuna wrote:
Hi,

Then how do explain the web page at the Attwood site which essentially states that modifications will void the warranty?

While Atwood's claim is actually illegal, it doesn't matter because Cheap Heat will cover the furnace's warranty if the manufacturer will not. I wish I had a dollar for every time you have been told this.

pianotuna wrote:
Hi,

If you have a 30 amp service then the cheap heat won't meet your needs. If you have a 50 amp service--then there is no need for multiple cords to run heaters.

I have a 30 amp service, so I do indeed have to run more than one shore power cord.

I suggest you install the biggest possible unit, since you have already proved that the smallest one and the medium size one are NOT going to meet your real life needs.

Interesting about the start up and electric motors. Does it apply to A.C. (120 volt) motors too?

So the bearings in a motor never wear out?

2-MTnesters wrote:
Over Thanksgiving We used our Montana as an additional bedroom for relatives that were in visiting from Texas. We had the furnace set at 65f during the day and 70f at night. We also had 2 space heaters running continuously in addition to the gas furnace. 1.5 30lb tanks of lpg were consumed during this time frame. Where we live I pay right at $25 to fill a 30lb cylinder. At the rate of consumption of 1.5 tanks of propane per week it would only take 13.5 weeks to have spent $500! For me this is a no-brainer, I would rather spend $500 on the Cheap Heat system and have it paid for in 1 season than to have to run numerous small electric heaters in addition to running the gas furnace and having to worry about running out of gas! Speaking only for myself, the Cheap Heat system is what I'm going to purchase for my camper because it is more practical for MY needs. I don't want electric baseboard heaters or stand-alone electric heaters in the middle of the floor, I don't want multiple extension cords run from the rig to the power pedestal and I also want heat in the basement to keep water lines, drains and valves thawed like the factory system is intended to do. Also, if the furnace blower has to run longer with the electric add-on that's fine, the life of an electric motor is NOT shortened by running, it's shortened by the max amp draw of the start condition.

How do you know the smaller version of Cheap Heat will not meet his needs? Back up your claims with hard facts, not your opinions. Keep in mind he is in Texas, not Canada. It doesn't get down to -20° very often (to put it mildly; the coldest I ever saw was 9° and that was 40 years ago when it was colder than it is now).

The bearings will last for so long, whether used on electric heat or on gas heat. If you weren't using electric heat, you would be using gas heat, running the blower. In fact, the fan motor bearings should last longer when used on electric heat since they won't get as hot and they are running at a slower speed.

Why do you insist on denigrating Cheap Heat when it is so obvious you know so little about it, especially after several people, including people who actually own and use Cheap Heat, keep disproving your ridiculous allegations?

pianotuna wrote:
Hi harold,

No need to call. Here it is on a web link. I'll make it a clicky for you. Cheap Heat Info Notice

harold1946 wrote:

pianotuna wrote:
Hi,

Then how do explain the web page at the Attwood site which essentially states that modifications will void the warranty?

I suggest you call Atwood and have them explain it to you.
In actuality the furnace is not being modified. The system is an aftermarket add on, and does not alter the furnace.
Think if it like adding a receiver hitch to a truck. Does that void the truck warranty?

That has been on the web for over 4 years and is not enforcable per the Magnusson-Moss Act of 1974.
Just because something is on a website does not make it fact. Like I said, call Atwood, then quote the law to them. They will promise to remove it, but they never do.

Hi harold,

No need to call. Here it is on a web link. I'll make it a clicky for you. Cheap Heat Info Notice

harold1946 wrote:

pianotuna wrote:
Hi,

Then how do explain the web page at the Attwood site which essentially states that modifications will void the warranty?

I suggest you call Atwood and have them explain it to you.
In actuality the furnace is not being modified. The system is an aftermarket add on, and does not alter the furnace.
Think if it like adding a receiver hitch to a truck. Does that void the truck warranty?

pianotuna wrote:
Hi,

If you have a 30 amp service then the cheap heat won't meet your needs. If you have a 50 amp service--then there is no need for multiple cords to run heaters.

I have a 30 amp service, so I do indeed have to run more than one shore power cord.

I suggest you install the biggest possible unit, since you have already proved that the smallest one and the medium size one are NOT going to meet your real life needs.

Interesting about the start up and electric motors. Does it apply to A.C. (120 volt) motors too?

So the bearings in a motor never wear out?

2-MTnesters wrote:
Over Thanksgiving We used our Montana as an additional bedroom for relatives that were in visiting from Texas. We had the furnace set at 65f during the day and 70f at night. We also had 2 space heaters running continuously in addition to the gas furnace. 1.5 30lb tanks of lpg were consumed during this time frame. Where we live I pay right at $25 to fill a 30lb cylinder. At the rate of consumption of 1.5 tanks of propane per week it would only take 13.5 weeks to have spent $500! For me this is a no-brainer, I would rather spend $500 on the Cheap Heat system and have it paid for in 1 season than to have to run numerous small electric heaters in addition to running the gas furnace and having to worry about running out of gas! Speaking only for myself, the Cheap Heat system is what I'm going to purchase for my camper because it is more practical for MY needs. I don't want electric baseboard heaters or stand-alone electric heaters in the middle of the floor, I don't want multiple extension cords run from the rig to the power pedestal and I also want heat in the basement to keep water lines, drains and valves thawed like the factory system is intended to do. Also, if the furnace blower has to run longer with the electric add-on that's fine, the life of an electric motor is NOT shortened by running, it's shortened by the max amp draw of the start condition.

I do have the 50amp service on my camper so I will be getting the largest unit that my furnace will allow. As for the motor remark, when an electric motor first starts up it will draw max amps. When this occurs heat is generated in the stator or windings, more so than during normal run conditions. Over time, this increased temperature will break down the varnish on the windings and will degrade the insulation on the internal wiring thus causing a short. This does apply to 120v motors as well. This is why on large motors there is usually a Soft Start installed which lessons the heat and strain on the mechanical components on the motor which in turn extends the life. And yes, bearings will wear out over time as well but a significantly cheaper repair than replacing the entire motor in most cases.