Question OASIS (AQUAHOT?) When to use Electric Heat vs. Diesel Burner

[Neal]

I have ITR OASIS in my Newmar Ventana but this discussion may apply to other systems of the same setup with electric heat elements and a diesel heat elements. In my OASIS CH-50M the electric elements are 5K BTU each (2 elements) and a 50K BTU diesel burner. My question for the gang here is when do you use which? This is also weather dependent as this is very different in summer heat vs. winter so lets focus on cold climates where we need house heat and hot water.

It seems to me that the electric burners can heat the house to an extent and I have no problems with electric only heat when in storage for winterization. I'm in Tucson and the nights are cold near freezing. As others I prefer not to burn diesel when I don't have to but the heating is much more efficient with the 50K BTU backed heating (diesel burner) so the fans run less, etc. Last night I was on electric heat only and I'm not sure it did so great possibly struggling to maintain my 70 deg setpoint (which is lower than most I assume, others probably like it warmer). I may have been cold because of the lower setpoint but the discussion still remains. What are your rules of thumb as to when you use diesel burner vs. electric heat for HEATING.

As for water, in the winter I always use diesel burner. I'll turn it on at least 10 prior to shower time such as when I take fido to do her business. Electric elements can work fine I just prefer unlimited very hot water. I probably need to test this again as I've spent far too much time not knowing that AC 2 wasn't working and recently finally fixed this saga by replacing the failed relay.

When do you use Electric vs. Burner in cold climate ops?

 

[Kevin D Pem]

I never use electric unless I am not paying the electric bill. OK I'll put it another way. I wouldn't run a generator for heat.

 

[Buly]

I'm using the Oasis more like Neal, except that we have two small 1500W heaters to help, and sometimes We use the heat pumps. lots of options

 

[CaptainGizmo]

Neal, even the best Electric heating system can’t keep up with cold temperatures and still keep your hot water hot.

Yes, floor heat helps a lot. But, my rule of thumb has been to keep the burner on when temps are below 45°.

In fact, just a couple nights ago, my water was only like warm after having JUST my electric heat on for the night...temps were in the high 30’s and it wa too much for it to handle.

 

[Rich-MLsRV]

I use the Oasis when outside temps get below 45F. I find using only AC1/AC2 it takes too long to heat up the coach to 73F in the morning, which is our preferred inside temperature. Overnight we have the thermostat set to 60F.

 

[Neal]

I hadn't heard of a temp at which to use diesel burner over electric heat elements (not heat pump but AC I/II). Interesting rule of thumb I'll take into consideration going forward. Thx

 

[Kevin D Pem]

Hey @Neal Keep an eye on the weather map. When the high we are experiencing in Yuma passes the winds may be a problem for high profile.

 

[docj]

I hadn't heard of a temp at which to use diesel burner over electric heat elements (not heat pump but AC I/II). Interesting rule of thumb I'll take into consideration going forward. Thx

One thing to consider in making this sort of decision is the relative thermal output of the diesel burner and its electric backups. In the case of my Hurricane, the burner is rated at 45,000 BTUs and one should assume that it has a thermal efficiency of ~60-70%. At 60% it is providing ~27,000 BTUs/hr. By comparison, the Comfort Hot heaters which I had installed to provide an electric backup were designed to operate off of a 20A circuit so I'll assume they provide roughly 2000 watts each of heating. Electric resistance heating is usually assumed to be 100% efficient. That means the electric heaters provide just under 14,000 BTUs/hr of heat. So the electric backup is providing ab0ut 50% of the energy of the diesel burner.

I've had no problem using the electric heaters down to ~28-30F but below that either supplementary room heaters are needed or I have to turn on the diesel. Just the other day I was able to demonstrate that my new heat pumps will operate well down to ~40F but they shut down entirely at 35F or below.

 

[Neal]

The electric heat has been working fine at around 36'ish outside. I just think they'll run longer to get to setpoint as the heat output is not as hot.

 

[AbdRahim]

What is Comfort Hot Heater? I can’t find these.

 

[docj]

What is Comfort Hot Heater? I can’t find these.

The Comfort Hot was something that was installed by Rixen's in Sandy OR. I've never seen it available for retail sale. Jim Rixen wired it so that it uses the two 20A A/C circuits which, obviously, aren't in use when you need to use heat.

 

[osuallen]

One thing to consider in making this sort of decision is the relative thermal output of the diesel burner and its electric backups. In the case of my Hurricane, the burner is rated at 45,000 BTUs and one should assume that it has a thermal efficiency of ~60-70%. At 60% it is providing ~27,000 BTUs/hr. By comparison, the Comfort Hot heaters which I had installed to provide an electric backup were designed to operate off of a 20A circuit so I'll assume they provide roughly 2000 watts each of heating. Electric resistance heating is usually assumed to be 100% efficient. That means the electric heaters provide just under 14,000 BTUs/hr of heat. So the electric backup is providing ab0ut 50% of the energy of the diesel burner.

The combustion process on a non-condensing boiler is ~80-82% efficient. There are some thermal losses through the boiler shell and circulation piping, however much of that heat loss is to conditioned space. The overall system thermal efficiency is probably more in the ~75% range.

 

[docj]

The overall system thermal efficiency is probably more in the ~75% range.

I'm quite willing a accede to your knowledge of this; the purposed of my post was illustrative not definitive.

 

[CaptainGizmo]

My head hurts.

When it gets cold, I turn the Electric Aqua-hot on.

When it gets really cold, I turn the Diesel Aqua-hot on.

?

@Neal, I can't recall specifically, but I think the OASIS manual does talk about lowest temp thresholds. I just looked up my Aqua-hot and it, indeed, suggests to switch to Diesel for temps below 50º. I find this to be very consistent with other's standard practice.

 

[docj]

When it gets cold, I turn the Electric Aqua-hot on.

When it gets really cold, I turn the Diesel Aqua-hot on.

If you have a heat pump your options are a bit more complicated. Heat pumps are more electrically efficient than the backup heaters on an Aquahot or Oasis. At temperatures temperatures above ~50F the coefficient of performance (COP) of most heat pumps will be ~2.5 which means they use 2.5x less electricity to produce the same amount of heat. Different brands will have different COPs but they're all going to be in the 2.5-3 range.

As the outside temperature falls the COP of a heat pump decreases, but as long as it can produce any heat at all it will still be at least as efficient as the backup heaters. I've now determined that my heat pumps do quite well at temps >45F and are reasonably effective in the 40-45F range (the front HP can't keep up with the thermal load of all the glass in the front of the MH.)

So my "rule of thumb" is to use the HP if the temps are predicted to be ~43F and to switch to the electric backup if the temps are in the 30F-43F range. Below 30F the diesel is the only option.

To those who may think this is too complicated to bother with, I would like to point out that this winter, with the heat pumps, I am saving ~$30/mo in electricity compared to my bills at the same location last winter. For us that represents a roughly 15% decrease in total energy usage.

 

[Kevin D Pem]

Wow guys. you have to many options. When I get cold I get up and put more pellets in the hopper.