Heat Pump vs Furnace vs Aquahot. Need to understand the pecking order

[CapnDean]

2008 Camelot 42PDQ.  I have triple roof units for AC as well as floor registers and even bay temp control.   I understand some of  the logic. But not all.

If I select heat pump on the thermostat, my ceiling units do a good job keeping my coach comfy except when its too cold for the heat pump to be efficient.   I understand that I need to choose furnace heat in this situation.   

Q1)  Will the thermostat make this decision for me?  Or must I physically get out of my warm bed and tell the thermostat to go to furnace mode?

Generally when staying aboard at an RV park, I select "electric" mode for the AquaHot.   It does well enough for 2 showers and dishwashing etc.  I prefer not to use diesel fuel when I can use park electricity.  

Q2) Should the AH be able to support furnace action without the diesel burner?  I think that the electric element is only 1500W and I just dont see how that would be enough to heat the coach.

Q3) Is there a way to adjust the "kick on" setting for the diesel burner so that I may use electric and only use diesel when electric is totally overburdened?   If I am on diesel & electric...  the diesel burner seems to take over a lot sooner than I would like.  (E.G.  I am shaving in the lavatory and by turning in the hot water a few times....I hear the diesel burner kick on).

 

and lastly....   i understand that the AH will use engine coolant heat to operate while I am in motion.  When I select "Engine preheat" mode on AH....   I get that it is trying to heat the engines cooling water....

Q3). Does it have any method of circulating it?  Or am I just sending a warm gallon or so of coolant to the engine when I start it?

 

I appreciate any input from those wiser in these devices!

Edited November 14, 2022 by CapnDean
spewwing

[SteveC]

The outside temperature and the inside temperature is the key. While the heat pumps will keep great temp inside down to about 35F (where it starts loosing efficiency) it doesn't do anything with warming the underbelly. People worry about fuel usage on the AH system because they read that the system uses .5 gallons per hour. What many don't realize is that is only when the burner is operating. If running the electric side of the AH along with the diesel side the diesel burner will only run when the electric can't keep up. That can be from zero fuel used when temps are around 40F to around 15 minutes per hour at 20F. This also depends on how warm you are keeping the inside of your coach. The water tanks are heated as well. When I arrive at a destination I turn both electric and diesel on. The diesel will run for a few minutes and then only run when I take a really long shower or the temps get low. I prefer the even heat and quiet heat of the AH over the heat pumps.

Now, regarding the engine heat switch. With your AH on, when you turn on the engine heat you circulate engine coolant through the AH boiler. The diesel burner will run some when you do this but the entire engine will warm up. When I'm staying somewhere cool I turn the engine heat on the night before we leave and the Cummins starts more easily.

I don't run my heat pumps unless traveling in cool weather. I start the generator and turn the front thermostat to 75 on heat pump. The dash heat can't keep up.

[willbo777]

The newer AH's only have one thermostat for the electric and the diesel, so when one comes on they both come on if both switches are on.  Our AH has 2 electric elements and handles heat pretty well down to the low 40's, then I turn on the diesel.  The heat from the engine does not require you to turn on the engine heat, it does it by itself.  We personally almost never use the heat pumps as we don't like the noise and it is not even heat and provides no heat to the basement.  Seems way superior to have the heat come out at floor level than at your head.  JMO.

[Tom Cherry]

I suspect that you have the same AH (450 - Maybe the "D" version) system that I do, but with Monaco you never know.  I DO know a few things for certain.

There are 4 Pumps in my system.

Pump 1 is a “ZONE” pump.  That is for Interior Heating. Zones 1 & 5 are supplied by this pump.  The “fan and thermostat” connections on the print show where they are located.  Thus, you can have a “interior” pump on and it is only supplying ONE zone….which means that the Thermostat is calling for heat there.

Pump 2 is also a “Zone” pump.  That is for interior heating, which is also roughly defined as a service bay.  Zones 2; 3; & 4 are on this pump

Pump 3 is the stir or recirculation pump.  It circulates the water from the top of the boiler to the bottom.  It is much smaller.  After reading the manual (attached), I have a little better understanding….which I “HEDGED” and said we have experts.  If you look at the flow chart in the first few pages, it describes the logic.  From what I READ, yes, the stir pump is circulating from either Diesel or Electric.  I also “conclude” (DANGEROUS” that it may run when the engine is heating.  Need to research more….but the 116 page manual is thorough.

The ENGINE coolant heating of the boiler is “automatic”….or that is the gist of my reading and knowledge.  There MUST be a bypass system in the pump or the circuit.  When you start to deprive, it takes typically 20 -30 minutes for the 195 DF water to heat the boiler.  There is also a 215 DF “high limit” switch, so, as long as you don’t “superheat” your coolant, you are OK.  I DID one caution….and it may be in the manual….but it sounds like common sense to me.  NEVER run the engine with the Preheat Pump on.  There is a small statement that says do NOT run the Preheat Pump when the engine is running…..and one poster on another site was emphatic that that WA$ a bad idea $$!.

That is an "Auto" thing.  So when the Diesel or Electric is ON the special "boiler" fluid must be circulated.  You of course know that this is a Potable solution and it has all sorts of special properties.  The original AH actually used Propylene Glycol and the newer ones use the potable one for safety

If you look at my schematic, When it is marked "FAN" that also brings on the Proper Pump that circulates the heat exchanger fluid to that particular zone or loop.  Your system is slightly different.  It MAY or MAY not be wired like the print.  SO....here goes.....

Fan 1 is for the Rear and Front Bedroom registers or heat exchangers.  Since I do NOT have the middle AC unit with a Furnace setting, my Bathroom Heater is tied into that circuit.

Fan 2 in yours (3 AC unit) will run the bathroom (2 speed blower) heater. Don't bet on it....but check it out....this IS Monaco.  LOL

Fan 3 is NOT USED.  This is listed in the manual or maybe in the brochure as “additional heating radiator”.  Can’t find it, but mine is configured that way.

Fan 4 is for the Bay Heat exchanger.  In some EARLIER models, at least in the Dynasty, you have to have the Bedroom system running.  I BELIEVE, from the prints, that the bay or service heat exchanger is free standing.  I do know from some cooler camping that the bay stays toasty.....but as folks have recommended, you really, in freezing temps, need to monitor it with a battery powered unit....and FRESH batteries.  You MAY have the Capillary Tube thermostat.....but in 2009, I KNOW that they cheated and just mounted (hidden almost) a snap disk on the floor or wall.  The hanging snap disk is for the Service or the Electric toaster.  You probably know that these fail due to a factory "Fix" that was a FIASCO.  There is a write in the files on how to fix the heater properly.  BUT, if you have the AH, then, it will automatically come on as the Thermostat is controlling it.  NOW, that assumes that you have a source of heat, either electric or diesel

Fran 5 is for the Front heat exchangers.

NOTE....there appears to be 2 check valves…one for pump 1 & one for pump 2,   Sometimes when a zone is running (fan on) and it is cold, then a gently to "Firm" tap is needed on the check valves as they  will stick.  THAT is why it is good to always run the system periodically.... Memory…may be wrong.  I THOUGHT that some of AH units had the check valves inside the plastic housing, therefore due caution was needed to tap or get it free.  LOOK AT THE MANUAL FOR A SPECIFIC SYSTEM.  Mine is here for reference with this comment…

A friend DID have a broken Engine Recirculation pump on his way to the ABQ festival.  That was in 2013 and added around $250 to his “PM bill”.  He had to stop and do some exploratory surgery and connect the in and out hoses to continue to drive…GREEN COOLANT everywhere.

NOW....some more information.  There is only ONE thermostat in my system.  It is ON @ 155 & OFF @ 180 DF. It will control BOTH the Diesel and the Electric.  SO, if heating is needed to get the boiler up to Temp, then when the Thermostat calls for heat... BOTH COME ON.  In the earlier years on the Dynasty (maybe on the crossover years when the Camelots and Windsors were the same), there MAY have been dual thermostats.  The differential was around 15 DF and the Electric came on.  If it could not satisfy demand, then the diesel kicked in.  I BELIEVE that all the AH units now only have ONE....but that is memory from talking to AH tech.  
 

OK….some notes and I had done this before.  The diesel burner puts out 56K BTU/HR.  The 1650 watt electric is around 5,600….or 10% of the capacity of the diesel….so when my GD started taking a shower and was 3rd in line, she screamed…TURN ON THE DIESEL….yes at 10 years old….she knew that.  Second, the rated capacity of the boiler is 1.5 GPM and the normal AquaTech/Remco RV55 is 5.5 GPM.  Full flow showers will eat into an electric supplied boiler heater….

You can download here or on the AH site….just pull your model number.  Easy to find.

https://www.aquahot.com/files/service_manual/450-DE2 Service Manual Rev C.pdf

NOW to your comments and maybe questions about the overall system and the thermostats and the HP.

I use the HP mostly.  However, they do loose capacity. I have been "TOLD" by Dometic and Monaco (the OLD tech support) that the Furnace will come on as "AUX" heat if the HP are not keeping up.  Obviously, they need the Diesel ON.  I was also told that you could when the AUX is on.  I have NEVER seen that....so I don't understand it.  BUT, if it is cool and the HP are running all the time....I just switch to Furnace. I will switch back in the morning when we wake up as usually the HP will work well there. How you use it and whether or not your "Thermostat" calls for AUX is strictly a decision based on comfort and such.

I DO know that the front HVAC is PUNY or undersized in cold, especially windy days.  I learned that on bringing the Camelot home from Florida to NC on a day it was 20 odd DF when we hit SC.  I knew VERY LITTLE.  Have learned some things since then.  SO....your method of keeping the front warm might work for you. BUT, it would NOT work for me that day as the ambient was below the practical setting of the HP.

This is what I do and I learned it from several members who had experimented.  Turn the HVAC to MAX AC.  Turn the temperature control to MAX HEAT.  There is a thermostat or a mode that will keep the compressor from coming on.  You also ELIMINATE all the incoming FRIGID AIR.  Any OTHER setting will  open the damper and you defeat the or overpower the Coolant HVAC power.  NOW, that does INCREASE the risk of moisture.  BUT, I find it works well.

I actually had to turn ON the Diesel burner and the Front Thermostat on that Friday.  That kept it comfortable. If you also leave the rear bedroom sliding door open, you get a LOT of heat from the engine that will migrate up front.  Turning the rear AC to Fan LOW will keep it circulating.  You might try that.....

The next is to FIX ALL THE AIR LEAKS.  Frank McElroy spent a great deal of time isolating and fixing all the cracks and crannies and poor assembly "joints" in his 2008 Dynasty. I don't do that much cool weather travel or camping.  SO, I have not gone through and done this.  I can't remember, but MAYBE turned on all his ceiling fans and was exhausting air and used his HAND to isolate WHERE the cold air was coming from.  He then fixed each one and finally got the front cap sealed.  He might chime in to correct and/or expand on what he did, but he said it make a great impact on traveling comfort.

That's about it.  If I am wrong, I know that the real experts will correct.  But that is the macro view with a little low level advice.

 

 

Aquahot and thermostats.pdf

Edited November 14, 2022 by Tom Cherry
Edited for corrections and clarification….see italics for changes

[Old Dog]

Another way of heating the interior: Portable electric heaters. Most of the parks I stay at don't meter electric so we use anywhere from 1-3 1500 watt little portable heaters in conjunction with a factory installed base board heater in the kitchen. It's been good to temps down to 16 degrees. Saves on diesel, so much so that I had not run the aquahot for 2 years then when I did need it the nozzle was clogged. Running it every 2-3 months has solved that issue. I also use up to 3 Golden Rods in the basement area to argument the small aquahot heater.

They only time we use the diesel mode is test/maintenance runs. Of course you have to be mindful of the potential fire hazards and distribute the electrical load.

[96 EVO]

What Bill B2 says!

Your newer model 450D has only one pair of boiler fluid thermostats, so, if you leave both electric and diesel switches turned on, when the boiler fluid temp gets low enough, both heating methods come on at the same time!

The electric element is 1650W, but your right, it's not going to keep your coach close to 70deg, unless it's about 60 outside.

As far as controlling the systems, it's all up to you! I've experimented many times with my AH up to full temperature with heat pumps on and not able to raise the temperature of coach, and the thermostat has never switched to 'Furnace Mode' on it's own! 

[Tom Cherry]

9 minutes ago, 96 EVO said:

What Bill B2 says!

Your newer model 450D has only one pair of boiler fluid thermostats, so, if you leave both electric and diesel switches turned on, when the boiler fluid temp gets low enough, both heating methods come on at the same time!

The electric element is 1650W, but your right, it's not going to keep your coach close to 70deg, unless it's about 60 outside.

As far as controlling the systems, it's all up to you! I've experimented many times with my AH up to full temperature with heat pumps on and not able to raise the temperature of coach, and the thermostat has never switched to 'Furnace Mode' on it's own! 

Amen to that, Bro.  Never saw it….and just control it myself….

[Georgia Mike]

Tom you stated the the circulation pump runs when the boiler is on diesel or electric. I thought that high pitch wining noise was the pumps running but I only hear that when it’s on diesel never on electric. In fact mine is quiet as a mouse on electric so is there a problem with mine? 
when I run the ah on electric only I have plenty of hot water and have used the furnace mode and it puts out heat but not as much as when it’s in diesel mode. 

[96 EVO]

The high pitch whine you hear on diesel is the burner motor which drives the fuel pump, and exhaust fan that pushes the air / fuel mixture into the combustion chamber, then out the exhaust pipe.

Edited November 14, 2022 by 96 EVO

[Tom Cherry]

55 minutes ago, Georgia Mike said:

Tom you stated the the circulation pump runs when the boiler is on diesel or electric. I thought that high pitch wining noise was the pumps running but I only hear that when it’s on diesel never on electric. In fact mine is quiet as a mouse on electric so is there a problem with mine? 
when I run the ah on electric only I have plenty of hot water and have used the furnace mode and it puts out heat but not as much as when it’s in diesel mode. 

Remember I said I was NOT the expert….just trying to do an overview.  

YES….as best I can read, the small Stir or Recirculation pump comes on….to keep the boiler and the antifreeze circulated.  You can read that in the Pump 3 section of the manual link that I just posted.

OK…..I also read more and removed some of the fuzz from my brain.  I mistakenly called the fans or radiators “PUMPS”.  I have edited my original post and verified the info….save a specific sentence that says the STIR PUMP ALWAYS RUNS….  See the Italicized changes….

Thanks for keeping me straight….folks say that is a full time job… LOL.

[Paul Busch]

I am missing something? A couple weeks ago my aquahot quit working on the electric side and also diesel burner wouldn’t work. I pulled the inspection panel off and the controller box off the check wires and it started working again? I assume I had a loose connection and maybe it would be ok. Last fall my float switch broke off and nothing worked as I was getting a low boiler fluid message. I replace all the sensors, float switch, high limit sensors for the diesel burner and electric element along with a new electric element. All was working good until a couple weeks ago and again yesterday. I pulled the diesel burner and installed a new injector and fuel filter. I can not seem to get either to work now. There are only three fuses that I know of and 2 1 amp in the CPU. Any one know what else to look for?

paulb

[Tom Cherry]

2 hours ago, Paul Busch said:

I am missing something? A couple weeks ago my aquahot quit working on the electric side and also diesel burner wouldn’t work. I pulled the inspection panel off and the controller box off the check wires and it started working again? I assume I had a loose connection and maybe it would be ok. Last fall my float switch broke off and nothing worked as I was getting a low boiler fluid message. I replace all the sensors, float switch, high limit sensors for the diesel burner and electric element along with a new electric element. All was working good until a couple weeks ago and again yesterday. I pulled the diesel burner and installed a new injector and fuel filter. I can not seem to get either to work now. There are only three fuses that I know of and 2 1 amp in the CPU. Any one know what else to look for?

paulb

Not much input from me.  IF the total panel is dead, I am assuming that you have 12 VDC incoming.  The interlock switch would, per the manual, shut down the diesel.

You sound quite knowledgeable.  Assume you have read Section 6.  I think that would be what AH Tech might suggest.  Give them a call and and see what they have to say....

[96 EVO]

10 hours ago, Old Dog said:

Another way of heating the interior: Portable electric heaters.  

I have began doing the same.

Figure I may as well save the remaining life of my HP's for cooling in the summer. Portable heaters are relatively cheap, and easy to change out.

Air conditioning..... not so much!

[Paul Busch]

Tom, thanks I will call them. The panel doesn’t appear to be dead. Just not turning on the heat.

paulb

[Frank McElroy]

14 hours ago, Tom Cherry said:

 

The next is to FIX ALL THE AIR LEAKS.  Frank McElroy spent a great deal of time isolating and fixing all the cracks and crannies and poor assembly "joints" in his 2008 Dynasty. I don't do that much cool weather travel or camping.  SO, I have not gone through and done this.  I can't remember, but MAYBE turned on all his ceiling fans and was exhausting air and used his HAND to isolate WHERE the cold air was coming from.  He then fixed each one and finally got the front cap sealed.  He might chime in to correct and/or expand on what he did, but he said it make a great impact on traveling comfort.

 

Yes. air leaks on my 2008 Dynasty were a huge issue.  At the time we were in Kansas helping out with the birth of one of our grandchildren and temps dropped down to the teens.  (BTW, when exiting the coach rule #1 check for ice on the steps - don't ask me how I learned that lesson!)

The biggest problems were huge air leaks between the fiberglass front cover and where it meets the dash just below the windshield.  I opened the generator door and could stick my hand in the gap.  I used black spray foam (HD in the landscape department) to seal this gap.  Another area is where wiring came up though the floor to the left of the drivers seat.  Once again, spray foam solved the problem.  Also check under the slides for gaps where the slide centering rails have air gaps.  Small pieces of fiberglass insulation solved those floor draft problems.  I also left the step well floor extended.  After these changes, the dual aquahot electric heaters could maintain 70 deg inside when outside temp dropped to 40.  But diesel was required if outside temps dropped below 40.  We also had remote temperature sensors in the service bay to verify that the aquahot heat exchanger was keeping temp above freezing.

Now, for the unintended consequences. 

After sealing all the air leaks under the dash - WOW, the dash AC now works amazingly well and so does the dash heater - no cold feet when driving in freezing weather!

 

[trailmug]

Coolant will flow through the engine coolant loop and warm up the AH boiler whenever the engine is running. I find that's enough for space heating into the 30s once the engine comes up to temp. The preheat pump will force coolant through the engine when the key is off, but with the block heater, I don't find much of a need for it. I suppose if you were camping off grid it would be a good way to get engine block heat using diesel. My experience is that the preheat pump is prone to failure. Ours was broken, I replaced it, and now the replacement doesn't work. The old pump models aren't available anymore and you have to adapt the plumbing fittings to a new size.. IMO, not worth the hassle.

[96 EVO]

1 hour ago, trailmug said:

Coolant will flow through the engine coolant loop and warm up the AH boiler whenever the engine is running. I find that's enough for space heating into the 30s once the engine comes up to temp.  

Guessing your Sig came with the 675D?

That's about the temp I'm turning on the diesel burner while going down the road.

[Paul J A]

15 hours ago, Frank McElroy said:

Yes. air leaks on my 2008 Dynasty were a huge issue.  At the time we were in Kansas helping out with the birth of one of our grandchildren and temps dropped down to the teens.  (BTW, when exiting the coach rule #1 check for ice on the steps - don't ask me how I learned that lesson!)

The biggest problems were huge air leaks between the fiberglass front cover and where it meets the dash just below the windshield.  I opened the generator door and could stick my hand in the gap.  I used black spray foam (HD in the landscape department) to seal this gap.  Another area is where wiring came up though the floor to the left of the drivers seat.  Once again, spray foam solved the problem.  Also check under the slides for gaps where the slide centering rails have air gaps.  Small pieces of fiberglass insulation solved those floor draft problems.  I also left the step well floor extended.  After these changes, the dual aquahot electric heaters could maintain 70 deg inside when outside temp dropped to 40.  But diesel was required if outside temps dropped below 40.  We also had remote temperature sensors in the service bay to verify that the aquahot heat exchanger was keeping temp above freezing.

Now, for the unintended consequences. 

After sealing all the air leaks under the dash - WOW, the dash AC now works amazingly well and so does the dash heater - no cold feet when driving in freezing weather!

 

Use  a trouble light at night in the Generator compartment and have some one inside the coach spot the light coming thru to the coach interior area around the firewall . That's how i found the areas needing attention. 

[CapnDean]

Lots of good input here!   Thanks to all who took the time to report!    I’m in year 4 of this 2008 Camelot 42PDQ-   It had 32k miles on it in 2018 when I bought it.   Now has 45….    Still learning!

[Tazmanian Martje]

The cab area I guess I need to spray foam. drove back from Wisconsin bird hunting trip and froze my legs, hands and feet off.  was bundled up like Nanuuk of the North.  To top that off, my hubby(driving Behind me, don't ask why, noticed something flew off the roof.  Did he tell me?  NOOO!  I go into the bathroom and it is frigid plus wet.  look up and the vent cover is missing!  
So since we have been back I m doing repairs.  Next repair is the Aquahot. no heat in house, replace 230 Deg limiter, clean diesel burner, replace nozzle etc.  and flush the entire system. just waiting on the antifreeze to get here.  At the Moment re reading the service manual for AHE 100-02S.  Say a prayer for me.