Thread: Aux heat on heat pump

Is there a requirement to have aux heat with a heat pump?

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If you don't have any heat strips (aux heat) the defrost cycle will be very cold air!

Originally Posted by Rick Cantrell

Is there a requirement to have aux heat with a heat pump?

No, unless you need it to meet the heating load requirements when it gets really cold. Most manufacturer's sell the heaters seperately from the AHU and you plug in just what you need, (i.e. 5, 10, 15KW strip heaters.)

Originally Posted by Jim Luttrall

No, unless you need it to meet the heating load requirements when it gets really cold. Most manufacturer's sell the heaters seperately from the AHU and you plug in just what you need, (i.e. 5, 10, 15KW strip heaters.)

Jim, have you seen any with no heat strips. How do they handle the defrost cycle?

Originally Posted by Rick Cantrell

Is there a requirement to have aux heat with a heat pump?

Originally Posted by Jim Luttrall

No, unless you need it to meet the heating load requirements when it gets really cold.

My answer would be based on the same requirement as Jim's answer (or at least what I think Jim is referring to), but I would have said it this way: Yes, because you most likely need them to meet the heating requirements of:

From the 2006 IRC. (underlining is mine)

- R303.8 Required heating.

When the winter design temperature in Table R301.2(1) is below 60°F (16°C), every dwelling unit shall be provided with heating facilities capable of maintaining a minimum room temperature of 68°F (20°C) at a point 3 feet (914 mm) above the floor and 2 feet (610 mm) from exterior walls in all habitable rooms at the design temperature. The installation of one or more portable space heaters shall not be used to achieve compliance with this section.

Now *IF* the heat pump can accomplish that by itself, then "maybe not", but with a heat pumps effectiveness dropping as it approaches freezing, if you are above the freeze line (which is basically I-10 across the top of Florida through to Texas then up to California), auxiliary (emergency) heat strips will most likely be required to meet that requirement.

Originally Posted by Vern Heiler

Jim, have you seen any with no heat strips. How do they handle the defrost cycle?

No, we need the extra heat around here since our overnight lows can get into the teens pretty regularly with the occasional single digit. Anywhere that is gets below 25 to 30 will needs some additional heat unless it is a two stage designed for cold weather.

If it is warm enough not to need the extra heat, then defrost is also less of an issue too.

Originally Posted by Jim Luttrall

No, we need the extra heat around here since our overnight lows can get into the teens pretty regularly with the occasional single digit. Anywhere that is gets below 25 to 30 will needs some additional heat unless it is a two stage designed for cold weather.

If it is warm enough not to need the extra heat, then defrost is also less of an issue too.

I have seen outdoor units as solid as a block of ice at temps well above freezing due to faulty defrost cycles.

When the system goes into defrost it is in the cooling mode and a heat strip is needed to temper the cold air blowing into the home. So I would say auxilary heat is always required on a heat pump!

Aux strips would make a better system in terms of comfort, but they don't make the system defrost any better, the heat for defrost comes from the indoor air temperature.
A properly designed duct system for a heat pump should keep air flow off of the occupants anyway since the discharge during heating could easily be 80 degrees or less, not comfortable to have blowing on your 98.6 skin.
Of course talking reality, I RARELY see a properly designed duct system with a heat pump, so using strips to temper the air during defrost may be desirable. I have never actually checked to see the number of systems that use aux strips for that purpose.

Back to the air flow thing, If you see a straight vane three way throw grill mounted in the ceiling on a heat pump, it is wrong in my opinion. It should have a curved discharge vane to direct the air flow across the ceiling, not blowing on the occupants. Heat pump discharge temperature is too cool and will deliver an unacceptable "drafty" condition if the air flow is not right.

Jim,

We have a heat pump and when it is running it is putting out nice warm air when it blows on us???

We keep the thermostat at 72 degrees F, if that makes a difference.

Not everyone is fortunate enough to only need to heat from 68 to 72
Add 20-25 degrees to 72 when it's 60 degrees outside and it's not too bad.
Add 10-15 degrees to 65 when it's 30 degrees outside and it is a different story.
In reality NO duct system should be designed to blow directly on the occupants, but with heat pumps the comfort issue really shows up.

Originally Posted by Jim Luttrall

Not everyone is fortunate enough to only need to heat from 68 to 72 .

Hey! I'll have you know it is *49* out right now!

Even when it got down to around 28 a couple of weeks ago, the air coming out still felt warm. Of course, though, the auxiliary heat was likely on them.

You know those winter storms which have come across everyplace in the last couple of weeks? They came through here too! (That's when it got down to 28. )

Jim and Jerry
Thank you for your answers.
One of the reasons I ask is because I have seen some homes that had heat pumps that did not have aux heat. This made me wonder if the aux heat is required (needed) in this area.

Friday I talked with the city inspector, and asked him.
He said pretty much the same thing.
No requirement to have aux heat, the only requirement is to be able to provide enough heat.

The other reason I asked is that, I am in the process of remodeling 3 rental homes. Pretty much complete rehabs.
All 3 are similar, and in about the same stages.

Convert from 30/60 amp to 200 amp total electric, complete rewire
(rough in inspected Feb 23rd)
All new water and sewer (rough in inspected 3/6)
HVAC, install ducts and heat pump. (Have not started on this yet)
This is why I wanted to know.

I have another question, but I'll have to ask it later, because my crew just came in for work.

Again thank you for your answers.
Rick