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Old 12-03-2011, 07:14 AM   #57
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Again, assuming that sufficent current is available to power a central heating system. My point is that any variance between strip heaters and a strip heat-based central heating system is one of SIZE, not of fundamental DESIGN, and SIZE is strictly a function of Power (Wattage) = EI (Voltage x Current).

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Old 12-03-2011, 07:25 AM   #58
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That would be correct. Its a matter of a single larger heatstrip being used in a single unit as opposet to several smaller ones in seperate units.
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Old 12-03-2011, 08:27 AM   #59
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Normaly the added heatstrip for rooftop ac will put out about 1,500 watts or 5,000 BTU,
The electric central heat is capable of 5,000 watts or around 17,000 BTU, so in essence three heatstrips or 1,500 watt space heaters would not equal the BTU output of a single larger heat element.
Another problem is one cannot get heatstrips for roof top heat pumps (odd, that).

A heat strip in a roof top A/C will only deliver heat from the unit or ceiling ducts. One in the furnace (actually, in a plenum attached to the furnace) will deliver heat from floor vents, which is noticeably more efficient than from ceiling vents, and can also heat any basement or underbelly areas.
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Old 12-03-2011, 02:21 PM   #60
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One test I wish someone would do when installing one of these is to measure the temperature of the heated air when burning gas at the ducts before and after installation. It would be an easy way to see if the electric heating element significantly affects air flow.
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Old 12-03-2011, 03:08 PM   #61
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One test I wish someone would do when installing one of these is to measure the temperature of the heated air when burning gas at the ducts before and after installation. It would be an easy way to see if the electric heating element significantly affects air flow.
I used an airflow meter before and after installation and found no significant restriction, less than .14 cfm. at each registers through the heating element. I think this gives a much better indication of any restriction than temperature could.

Every rooftop ac installation manual I have seen states that heatstrips can not be used with ceiling ductwork.
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Old 12-03-2011, 05:24 PM   #62
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LADYFITZ

I will check heater vent temperture the next time I hook up my camper to shore power. I'm in the process of tearing my old shop down at my house. I had to move my camper off my pad to tear down the old shop. I should have it back on the pad next Saterday. If the weather cooperates,
i's looking like rain early in the week. The temperture is in the 70's today, big change. I do have a heat temperture gun to check the vent tempertures on both the electric and gas side. I'm going to check into a damper valve that I can remote control or set to open by a thermostat control solenoid, for the extra duct that I ran to the tank compartment. I was just thinking that I don't need to heat the under compartment to the same temperture as the inside of the camper. I'm thinking that if I can set the underbelly temp to around 50 degrees would be good. will have to check the internett to see what they have to offer for this next project.
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Old 12-03-2011, 09:16 PM   #63
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I used an airflow meter before and after installation and found no significant restriction, less than .14 cfm. at each registers through the heating element. I think this gives a much better indication of any restriction than temperature could.

Every rooftop ac installation manual I have seen states that heatstrips can not be used with ceiling ductwork.
Thanks for the airflow info. I had suggested the temperature comparison to check for restriction because people are far more likely to have a thermometer than an airflow meter. Naturally, an airflow meter is more accurate.
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Old 12-03-2011, 09:22 PM   #64
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LADYFITZ

I will check heater vent temperture the next time I hook up my camper to shore power...
Thanks but our good buddy az bound has already covered that issue. I was concerned that reduced airflow could cause overheating of the heat exchanger but that is not likely to be an issue, especially since it isn't going to be used as often.
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Old 12-03-2011, 09:33 PM   #65
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Ok, humor an old lady. What am I supposed to be looking for?
My post, #12 in this thread, explains the amperage limitations.
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Old 12-03-2011, 11:31 PM   #66
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My post, #12 in this thread, explains the amperage limitations.
I don't know why you are bringing it up now but since you did, you made some bad assumptions in that post which lead to equally bad conclusions. Why are you so dead set on denigrating the Cheap Heat, especially when you have made it so painfully obvious you haven't the foggiest notion what you are talking about?

First, 17,000 watts? Nothing was said about 17KW. 17,000 BTU but not 17,000 watts. The max cheap heat draws is 5000 watts (the other two settings are 1800 watts and 3750 watts. All that was explained very clearly on the Cheap Heat website.

Second, to get that 5000 watt rating, one has to use 240v, not 120v. Since most, if not all RV panels, are not capable of safely and legally providing 240v, one has to install a separate panel to feed the Cheap Heat. Paw John has told us he used a 240v 30a disconnect box (or panel) to feed his Cheap Heat. He even posted some pictures of it. At 240v, 5000 watts will draw only 20.8A. That is only a hair more than two A/Cs will draw so is not likely to overload the service unless someone is goofy enough to run both A/Cs and the Cheap heat at the same time. All of this has been discussed in this thread and on the CheapHeat website.

Finally, you wrote in your post, "There would have to be a 240VAC conversion inside the coach for it to work (70A @ 240VAC). That leaves ~30A to power the rest of the RV." Where on Earth did you get those figures? Most 50A RV services provide only 50A at 240v (as mentioned in another post, there are a few 120/208v services) which equals 12,000 watts, not 100A 240v. The RV sees this as two separate 50A 120v feeds, still totaling 12,000 watts. There is no way you would be able to get 70A 240v from a 50A service so you sure as heck wouldn't have 30A left over!
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Old 12-04-2011, 10:44 PM   #67
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Ok LadyFitz, I give up. I should not have been on my computer the evening after surgery, really made a fool of myself.. One possible side effect of electric central heat is like this thread: metered electric for short-term parking.
That will eliminate the mfgrs. claim of cheap heat.
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Old 12-04-2011, 11:12 PM   #68
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Of course, electric strip heat in conjunction with heat pumps would be even more efficient.

Rusty
I don't think any heat pump manufacturer has heat strips as an option for them. I've had them with air cons, not worth the money. They just don't give enough heat to do very much.
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Old 12-05-2011, 08:53 AM   #69
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Ok LadyFitz, I give up. I should not have been on my computer the evening after surgery, really made a fool of myself.. One possible side effect of electric central heat is like this thread: metered electric for short-term parking.
That will eliminate the mfgrs. claim of cheap heat.
I do have to give you points for persistance. There are still plenty of places that do not meter short term parking. And, as has been stated before, there are those (such as myself) who feel the convenience of not having to refill propane tanks frequently and/or horse around with portable electric heaters (which would also be subject to metered electricity, btw) far outweighs the cost of the Cheap Heat, even if having to pay for the electricity. Even if propane can be delivered to someone wintering a CG or resort, it is usually only monthly. Having to wrestle with tanks between deliveries may not be an option for the elderly and the handicapped.

Btw, I could not read your link. It requires signing up to just read anything there and I do not trust websites that have that requirement.
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Old 12-05-2011, 09:00 AM   #70
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I don't think any heat pump manufacturer has heat strips as an option for them. I've had them with air cons, not worth the money. They just don't give enough heat to do very much.
When it comes to RV heat pumps, you are correct (residential models can have them). And, as someone pointed out earlier, ducted rooftop A/Cs also cannot have heat strips.
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