Which New Rooftop Air Conditioners?

[slowmachine]

I'm looking for some educated help in deciding which new rooftop heat pumps to purchase. I need to have them installed and running in the next three weeks. My current units are old enough and need enough help to make replacement more attractive than repair.

My 40ft Holiday Rambler currently has two 15-year-old Dometic Duo-Therm 13.5k BTU heat pumps run by a central 4-button thermostat. It is a ducted system, and the front and rear zones are connected through the ductwork on only one side of the coach. For power, I have a 50 amp shore power system and an Onan 7500 diesel generator.

I would like to hear from anyone who has resistance heat strips in their rooftop units as to how useful they are. How much cooler can the outside temperature get before the rooftop units cannot provide enough heat to keep the inside temperature around 70 degrees? As far as I can tell, only two of the current Dometic models are capable of being fitted with the heat strips.

Also, I am wondering if it makes any sense to replace the 13.5k units with 15k units. I know that oversizing residential heat pumps is not necessary a good thing. I believe that the higher-powered units' run-time can become so short that they are no longer effective dehumidifiers. My roof is white, and my walls are mostly white. Are the 15k heat pumps overkill?

[jesilvas]

If you were happy with 13.5K units, go back with that.

I would make both Dometic units because doing otherwise would make wiring hard. Get the Penguin II units, and the new CCC2 t-stat, that way all wiring is plug and play.

Heat strips are 5000W or so each, basically a space heater on high, but with proper wiring and ducted of course.

[docj]

Originally Posted by jesilvas

Heat strips are 5000W or so each, basically a space heater on high, but with proper wiring and ducted of course.

Heat strips are 5600 BTU/hr not 5000W; that's about 1640W (the same as a space heater). They are also not designed to be used with ducted air conditioners.

5600 BTU Heat Strip for Dometic Air Conditioners - Dometic 3101121.030 - Air Conditioner Accessories - Camping World

[slowmachine]

Originally Posted by jesilvas

If you were happy with 13.5K units, go back with that.

Unfortunately, I have no experience with the 13.5k units. I don't know if they are enough, or if 15k is too much.

[jesilvas]

Originally Posted by docj

Heat strips are 5600 BTU/hr not 5000W; that's about 1640W (the same as a space heater). They are also not designed to be used with ducted air conditioners.

5600 BTU Heat Strip for Dometic Air Conditioners - Dometic 3101121.030 - Air Conditioner Accessories - Camping World

Yep, you're right. I had doubt as I typed W and not BTU
Hey, I still said they were basically like a space heater on hi.

Originally Posted by slowmachine

Unfortunately, I have no experience with the 13.5k units. I don't know if they are enough, or if 15k is too much.

So you just bought it? So what's wrong with them to warrant replacement?

[Mr_D]

Will any heat pump accept heat strips? Last I looked into it there were none.

[slowmachine]

Originally Posted by Mr_D

Will any heat pump accept heat strips? Last I looked into it there were none.

Looking at Dometic's 2015 catalog, you may be correct. It shows heat strips for the cool-only units, but not the heat pumps. Dometic's literature is notoriously short on details, though. I'll call them later today and ask.

[slowmachine]

Originally Posted by jesilvas

So you just bought it? So what's wrong with them to warrant replacement?

To begin with, nearly every plastic piece is old, brittle, and broken. At least one control unit has a damaged circuit board. Thermostat does not work correctly. Badly corroded electrical parts in the outside section. At least one bad reversing valve. Many parts are no longer available from Dometic. I'm somewhat confident that they could be restored to working condition. If you add the time spent sourcing obsolete parts and making repairs, I'm guessing that the repair cost could be half the cost of new equipment.

[jesilvas]

Originally Posted by slowmachine

To begin with, nearly every plastic piece is old, brittle, and broken. At least one control unit has a damaged circuit board. Thermostat does not work correctly. Badly corroded electrical parts in the outside section. At least one bad reversing valve. Many parts are no longer available from Dometic. I'm somewhat confident that they could be restored to working condition. If you add the time spent sourcing obsolete parts and making repairs, I'm guessing that the repair cost could be half the cost of new equipment.

You probably are correct. The plastics are easy, but reversing valve is soldered in.

Just asking because a lot of people think they need replacing and it's something easy because they didn't do research, but you know what you're doing.

[slowmachine]

Phone call to Dometic confirmed Mr. D's suspicion. Heat pumps and heat strips never go together. My local shop is ordering a pair of 15k Penguin 2 heat pumps and a CCC2 thermostat.

[jesilvas]

I think you'll be fine w/two 15K units. If two is too much, just turn one off haha.

[slowmachine]

The thing that convinced me to go with the 15k is that 8 of my 12 ceiling registers are in the front living/kitchen area. A pocket door separates the kitchen from the bathroom/laundry and the bedroom. So, I have 3/5 of the MH that may be sufficiently cooled by a single 15k unit when we aren't using the bedroom. That's the theory, anyhow. We'll find out in July how that works in the real world.

[caninecop]

I was doing a search for upgrading our A/C and I saw your post. We want to upgrade the a/c and heat pump with the Dometic Penguin II 15K BTU air conditioner model 641816. With your upgrade was in mostly removing your old system and replacing it with the new or did it require renovation to fit your new system.

[slowmachine]

It's getting installed on on Wednesday. I'll post the details when it's done.



Mike
2000 Holiday Rambler Endeavor 40PBD
Freghtliner XC, CAT 3126B