Base/Support for Heat Pump Condenser Unit

nickr

I live in North Jersey and am looking for advice on how best to have my new 36,000 BTU condenser unit installed. It'll power indoor ducted/ductless mini split units for my home -- primarily for cooling but also for heat the majority of the year (with steam backup). The unit will be located in a grassy lawn area next to my house.

The options seem to be:

- place a plastic pad on the grass, put the unit on the pad, and call it a day (installer recommends this method)

- put a steel stand between the plastic pad and the unit, to lift it off the ground 12"

- use brackets attached to the foundation (installer recommends against this, as the foundation blocks aren't flat and so it'll be hard to get a tight fit with the brackets. I'm also worried about vibration being transferred to my small house)

- dig a rectangle, level and tamp the dirt, lay down a treated 4x4 permitter, and fill with sand/crushed gravel, as a base for either: a) the plastic pad with the unit on top of it, or b) add a steel stand between the pad and the unit

All recommendations/input appreciated! My priority is efficiency and longevity of the unit; aesthetics are secondary.

GGross

You need to raise it off the ground if you plan to use it for heat during winter months.

I like to use a nice pad, and then attach the stand to the pad.

12" or 18" stands, diversitech makes nice looking ones, rectorseal makes some less expensive ones. I like them both just fine. Many of these have two sizes, one for single fan mini split condensers, and one for dual fan condensers.

You can either pour a concrete pad, or purchase an appropriate size plastic pad, I have seen people use paver stones under the feet of the stand instead of a pad as well

i am not a huge fan of attaching wall brackets to your house. Technically nothing wrong with this method and sometimes it is all you can do, but there is a chance you will get vibration through the walls.

pecmsg

That unit needs to be above the average snow load for proper and efficient heating!

Jamie Hall

Depends a little, in my view, on the soil. If your soil is reasonably firm (you can walk on it without leaving much of a nent), I'd go with a plastic pad directly on the soil (level it out if need be) and then a stand. No need for a concrete or gravel pad -- they really aren't all that heavy, when the weight is distributed by the pad.

nickr

pecmsg said:

That unit needs to be above the average snow load for proper and efficient heating!

Thanks! Do you know how to determine a location's average snow load? My condenser unit supposedly goes down to -15 Fahrenheit, so I hope to use it almost the entire winter.

nickr

Jamie Hall said:

Depends a little, in my view, on the soil. If your soil is reasonably firm (you can walk on it without leaving much of a nent), I'd go with a plastic pad directly on the soil (level it out if need be) and then a stand. No need for a concrete or gravel pad -- they really aren't all that heavy, when the weight is distributed by the pad.

Makes sense. My soil seems pretty firm -- I have to really press down to compact it. I think we'll just level the bumpy soil and go with the pad/stand combo. Thank you.

nickr

GGross said:

12" or 18" stands, diversitech makes nice looking ones

Yeah I was worried about vibration.

My installer brought out a Diversitech stand but recommended against using a stand due to potential rust issues. Is there anything I can do to prevent the stand from rusting?

Jamie Hall

Rust? Keep it clean. Pay attention. And Rustoleum when you can't stand it any more.

nickr

Jamie Hall said:

Rust? Keep it clean. Pay attention. And Rustoleum when you can't stand it any more.

Words to live by.

EdTheHeaterMan

nickr said:

pecmsg said:

That unit needs to be above the average snow load for proper and efficient heating!

Thanks! Do you know how to determine a location's average snow load? My condenser unit supposedly goes down to -15 Fahrenheit, so I hope to use it almost the entire winter.

How long have you lived there? More than 10 years? YES? Then you have experienced the average snowfall. The National Weather Service also has the data. But that data does not know about how the snow drifts at your home or how the snow drifts exactly where the outdoor unit is located. You need to remember what your home looked like on that last blizzard that was national news in the last 10 years. Then mount the outdoor unit accordingly.

There is no metal with this Heat Pump riser That you place on the bottom of a outdoor unit that you then place on a plastic pad on the lawn. https://www.diversitech.com/heat-pump-riser-12-in

GGross

nickr said:

GGross said:

12" or 18" stands, diversitech makes nice looking ones

Yeah I was worried about vibration.

My installer brought out a Diversitech stand but recommended against using a stand due to potential rust issues. Is there anything I can do to prevent the stand from rusting?

I have been told the rectorseal stands are less prone to rust, for what its worth I have not heard feedback about rust issues on either in my area, I would defer to a contractor in your region if they experience issues with rust on them.

https://rectorseal.com/big-foot-dmss-single-unit-stand-b5551/

mattmia2

You could always build a little box out of concrete block filled with dirt and pour a pad on top of it like a little porch. Make sure it is big enough for whatever future unit might go on it.

nickr

The footprint of the stand's four square feet are wider than the plastic pad the stand will be placed upon, leaving about a 1" strip of each foot hanging off the edge of the pad (and thus two bolt locations on each pad hanging over the edge). This seems like an issue to me but the installer says it's OK. Is this a problem?

nickr

seems bad

pecmsg

What's under that pad?

It appears no site preparation was done. Just flatten the dirt and lay the plastic pad?

nickr

pecmsg said:

What's under that pad?

It appears no site preparation was done. Just flatten the dirt and lay the plastic pad?

That's right. Just leveled dirt.

pecmsg

Not high enough for a heat pump.
Ground heave WILL happen!

nickr

pecmsg said:

Not high enough for a heat pump.
Ground heave WILL happen!

15" elevation is insufficient? We almost Never get snow that high.

pecmsg

nickr said:

pecmsg said:

Not high enough for a heat pump.
Ground heave WILL happen!

15" elevation is insufficient? We almost Never get snow that high.

THats a Local thing.

pecmsg

Here's my personal unit. The posts are 36" down. My switch over point is 30°F, at that point I go back to HW Radiators. Not happy with Heat Pump heat when the cold NE winds blow.

hot_rod

Build a stand out of most any material. Maybe match the look of the building.
This is snow country upstate NY. Also under a roof pitch that dumps snow, so elevated quite a bit.

ethicalpaul

pecmsg said:

Here's my personal unit. The posts are 36" down. My switch over point is 30°F, at that point I go back to HW Radiators. Not happy with Heat Pump heat when the cold NE winds blow.

Should have gone with ground source, not air source!

To the poster, I wouldn't worry about that pad or the feet on it. Does that ground move around? No. The tiny overhang of those feet isn't going to matter.

bburd

One more point though: the holes in those feet are there for a reason. They are supposed to be screwed down. Otherwise normal vibration may cause the condensing unit to shift position and stress the refrigerant piping and/or electrical connections.

clammy

Usually on mini split equipment ,I first dig out and set 48 inch concrete lentials so they sit a few inches above grade and then mount my stand on that , this usuually keeps it well of the ground and as time passes the unit does not end up sitting in mulch and over grown weeds . It’s usually not a ac service guys responsibility to remove and get rid of the mulch that piles up against the condensing unit it does no one any good . I would not attach to your foundation due to sound possible being transferred and it does make it a **** to clean . The rector seal stand is fine as they all are and yes they rust like everything in life but by the time it’s an issue the u it will need replacement . I also would get rid of weeds and hedges that block air flow no good . Usually when a customer gets a mini split all those issues are pre discussed and planned not a as we go project especially on outdoor location ,but what do I know I quite sure that Fujitsu makes a pad and risers for it , I also believe all condenser pad are suppose to be 3 inches thick not 1 1/2 old stock according to code . . I don’t think I would ever just use 4 x 4 as riser soon or later they will rot the u may have an issue . In days of old they would have just poured a pad . If it’s a heat pump it should be above normal snow line to prevent the unit from being buried as basically for myself it common practice and would have been ironed out before any work was performed but that s me . Hopefully your contractor if familiar w what he s doing . Peace and good luck clammy

clammy

On another note the ground should be solid and tampered to prevent the unit from becoming lopsided ,usually I will get a few bags of gravel and tamp it down before setting a pad or lentials ,also lentials are great for setting boilers on when u don’t want to pour a pad or possible buy A dozen cap block and level and cement . Some food for thought .
Peace and good luck clammy

nickr

Well, it's in place. I agree that these issues should have been addressed before work started, but that's in the past. And don't worry, I'm going to cut the bushes back to give it space.

One issue though: it's really easy to rock the unit back and forth. Too easy in my opinion. Is this common and OK, or is it a liability/problem?

GGross

if it rocks it must be a bit uneven, I would want that remedied personally. I do wish they would get you a bigger pad, we use a diversitech 32x44 pad for the diversitech single fan mini split stands

many wholesalers sell those skinny short ones as mini split pads for people who are not installing a stand

mattmia2

If it can rock it can tip over if someone runs in to it or leans on it so it needs to be anchored better than that.