Only the air tempature at outdoor condenser and room t-stat control aux heat strips. With that said,can the handler be insulated? Sure but the effects aren't remarkable if handler factory insulation is intact. There is a recent trend where attic is insulated with spray foam. Some people incapsolate the ducts and handler except service panels of non-gas units. (Sure will be expensive to replace exchanger when time comes).

You can bet on the unit leaving factory with insulation and there is little reason why it might go missing but you can see. Just remove a service panel that accesses motor and/or coil. The panel as well as all other inclosures should have a fiber blanket and possibly foil faceing adheared to them. While unit is running during cooling season lay your hand on the exterior housing. Any area larger than 100 sq inches that is below about 80 deg F will benifit from additional insulation. In heat mode,maybe above 100 deg would be suspect of inadiquate insulation. Very rare concurn except in extreme tropical or artic climates. Poorly sealed or insulated ductwork is quite common.

insulation always needs to be installed in contact with
what is being insulated.

that said...I'd take a panel off & see the insulation inside.
it isn't much, but unless your unit is condensating heavily
it usually isn't worthwhile to insulate externally.
usually condensation is on equipment to supply plenum
where air is coldest. the condensation may be exacerbated
by duct leakage..plenum not mastic sealed to equipment.
condensation on supply plenum is usually from unsealed
duct take offs on the plenum. these too should be mastic
sealed.

if you do feel for some reason that you need to insulate
equipment, make panel insulation to fit panel so that
the panel can be removed for service.
ductwrap (R-8 foil faced ductwrap) is what you'd use.
you'll need, in addition to the mastic (not duct tape, not
foil tape...paint on mastic & a good mastic tape like Hardcast
brand #1402 mastic tape) duct stapler, fsk (foil scrim kraft) tape.

it works better if you have a helper to hold one side of the
ductwrap for you to wrap then staple the ductwrap.
apply fsk tape on seams, staple tape & paint mastic 'nickel
thick'.

look to spend $100 on duct wrap, $50 for duct stapler
plus costs of staples, mastic (s) & fsk tape. you can get
all at hvac supply.

why do you feel the need to add insulation?

best of luck.

Why do I feel the need to add insulation?

Well, first it would have been better if the supply ducts had been R8 than what did get installed. The air handler and supply ducts are all in the attic and so are outside of the insulating envelope of the house. I rarely run the unit in the summer time to cool the house. But I do run it for about 9 months of the year to heat the house. So, condensation is not the issue but keeping the air warm till it gets blown into the living space of the house is. If I can keep the air handler just a wee bit warmer in between heating cycles, its sure to help reduce my energy usage.

I'd put that effort into air sealing and duct sealing.
average home has 30% duct loss...that is money
you spend to heat/cool air that never makes it
into the living space.
mastics are cheap, and not rocket science to apply.

when ducts/equipment are in the attic the air
barrier between the attic and the living space below
sucks at every opening when unit is in use.
the air barrier is the sheetrock ceiling, which we
cut numerous holes into, and seal very few of them.

sealing these openings can be inexpensive, if you
are willing to work a caulk gun & invest in tape that
will provide a long seal.

these two things (duct & air sealing) are sure fire
ways to save on energy costs.

something you'd be willing to do?
we can walk you through it.

best of luck.

I've been masticing up the new return air can and the ducting that connects it to the air handler. By the time I'm done, all the return ducting should be air tight. I'll see about doing the supply ducts, particularly those vents you mention. Those connections were poorly done. Obviously, the contractor who renovated my house hired an HVAC sub who bought all the cheapest supplies, without consulting me on what I wanted, and installed them as cheaply and easily as possible to maximize his profit. I've been so infuriated over the matter. I complained through the BBB and everywhere I can. Still, contractor doesn't want to do anything about it. In short, the system is very inefficient and Im having to waste my time, money and energy altering something that should have been done right in the first place. Thanks for you help.

welcome.
just consider it an investment of your time for
improved efficiency tather than a waste of time.

it is frustrating to have to re-do work you paid
to have done.
but no one trains anyone to install ducts, much
less mastic seal them. that job goes to low paid
guy on the job, running duct inbetween fetching
& stepping for installers.

I am curious about how you would recommend sealing up the supply vents so that they don't just blow hot air into the sub-ceiling. All my supply vents are in the ceiling. Also, I don't really want to mastic the supply plenum because I don't want to have to remove the insulation surrounding it but.... Also, the old return air can also needs masticed but it has insulation on the inside of it. How necessary is that insulation when there is also insulation on the outside of it? Could I remove that inside insulation so that I can seal up the old return air can with mastic? Is removing that insulation permanent? Even though I plugged up the old return air can, I can hear air getting sucked through the sides of it which means its drawing in cold air from up in the attic and decreasing overall efficiency.

I just remodeled all the return ducts. I've tested it a few days and the results are amazing! There's no thermocline in my house any more. Its warm all they way down to the floor now. The installer claimed that a return couldn't be placed where I wanted because "it wouldn't fit." I'm facetiously pleased to prove them wrong. I'm thinking about posting a separate thread for that as that was quite an accomplishment. I took pics of the whole process.

It doesnt matter how hot or cold the environment of air handler. Its only going to come on when the temperature inside the house needs to go up or down. it could be -10 degrees in the attic but if you have set to 70* and its 70* in your house, then the air handler will not come on