Manual J question

[acobra289]

I have a copy of a manual J done on my house. If I am reading it correctly, the heating load is 43351 and cooling is 25503. CFMs = 1234
SQ Feet = 1933

A 3 ton system was recommended based on these numbers. (This also happens to be the size of the current system.)

Here is the system and it's performance numbers. The cooling numbers are close to a full 3 tons, but the heating numbers seem low. Especially if the heating load is 43351. Will this heat pump have any trouble heating my house until the temp gets low enough for the propane furnace to kick in?

XR-13 4TWR3036A
90% TUX1B080A9421A (74K BTU)
4TXCB036BC3

SEER 14.00 (35200 cooling)
HSPF 8.50 (31000 at 47* / 19600 at17*)
EER 11.80

Thanks.

[dash]

They will set it up to switch at the temperature needed ,no worries,I hope.

[BaldLoonie]

I see some issues!

First is the ratings. Not sure where you got yours but AHRI Directory says that HP with that coil and standard blower is 13.00 SEER and 8.20 HSPF. Heating output is low as usual with A-S/Trane.

Now, if your heat loss is 43K, you don't need that big furnace. The appropriate furnace would be the AUX2B060. Grossly oversizing a furnace means your actual efficiency would be reduced. You could have short cycling and you could cycle on the furnace's limit if the duct system isn't rather large.

If you like it ice cold, a 3 ton for just over a 2 ton load may be OK but the calcs if done right reflect the desired indoor temp. But the appropriate cooling (HP) unit would be 2.5 ton. Going nearly 50% oversized means short cycles and high humidity. And your 13 SEER will be effectively lowered due to constant cycling in mild weather.

As for changeover, I set A-S systems to change to gas 5° warmer than brands with good heating figures.

Personally I wouldn't want that system and hope our salesmen wouldn't suggest a system like that with those kind of gain/loss numbers.

[sparksandfan]

What was the sensible and what was the latent loads?

[acobra289]

What was the sensible and what was the latent loads?

It appears to me those fields are blank. There is a scan of the manual J below.

Bald, could you give me the ARI reference number for the match you are getting? Thanks.

[beenthere]

2421 Latent?

What area are you in again.

[acobra289]

Triad area of NC. Winston-Salem.

[beenthere]

Latent load sounds low.
Strange how it works out to require a 3 ton to get that sensible. Almost like the load calc was done to require the size you already have.

[acobra289]

Latent load sounds low.
Strange how it works out to require a 3 ton to get that sensible. Almost like the load calc was done to require the size you already have.

I could be wrong, but I don't believe this salesman ever checked the size of my old AC unit or asked me what size it was. I dunno.

[RyanHughes]

Was the salesman possibly trying to achieve 1200 CFM, thus suggesting a 3-ton unit?

[acobra289]

Was the salesman possibly trying to achieve 1200 CFM, thus suggesting a 3-ton unit?

I have no idea about that. He looked at the furnace in the garage and took measurements of it and noted the BTUs. Then we walked outside to look at the AC unit. I don't remember him looking on the back of it to get the size. Then we came back inside and he took measurements of all the rooms and windows and noted the window type (I have some old and some new). He checked where the supply and return vents were. And checked the attic insulation. He asked when the house was built and took a guestimate on the wall insulation. I don't recall him doing anything else, but it's possible I may be forgetting something.

I know NOTHING about manual J's, so I don't know what looks strange or not.

[sparksandfan]

Latent load sounds like a very tight house was assumed, but I see that the sheet says average construction.

If the sensible load is as stated, then as BaldLoonie said, a 2.5 ton air conditioning would more closely match. It would still have latent capacity for your area.

Is there a lot of wind wash in the winter? Are you on a hill or open pastures? High air change rate in winter?

[acobra289]

Latent load sounds like a very tight house was assumed, but I see that the sheet says average construction.

If the sensible load is as stated, then as BaldLoonie said, a 2.5 ton air conditioning would more closely match. It would still have latent capacity for your area.

Is there a lot of wind wash in the winter? Are you on a hill or open pastures? High air change rate in winter?

I think average would be accurate, definitely not "very tight". House is brick, split foyer. Faces southwest. Has a large window area in the foyer area (about 41 sq ft) This glass is single pane. I have put some "tinting" on it to help some. And front porch overhang also blocks some afternoon sun.

Not on a hill or open area. Not unusually windy that I'm aware of.

[acobra289]

Is it possible that he is slightly over sizing the heat pump to get the needed heating btus?

When he gave me the sheet and pointed out that it would cool to 75* on a 95* day. I asked him what if I wanted it to cool to 72 on an upper 90's day and he said it should do that. He said the 75 on a 95 was basically a "worse case" scenario day. Like if we had people over and there was cooking in kitchen and what not.

I hope this guy isn't full of crap. He is actually my best option so far. (And no, he is not the lowest bid.)

[beenthere]

Oversized A/Cs tend not to remove moisture real well. How did your old 3 ton do.

[acobra289]

Oversized A/Cs tend not to remove moisture real well. How did your old 3 ton do.

I guess it does ok. It's really hard to judge as it is probably about 10 years past it's prime. I'm pretty sure it's original to the house and the house was built in 73 or 74.

Right now the humidity is around 53% in the house. But the outside humidity hasn't been bad that last few days. It will get much worse come July and August.

[beenthere]

So did teh humidity get worse in the house last year, or was it able to keep the humidity below 55%.

[acobra289]

I can't say for sure. I have only been using the hygrometer for the past 5 or 6 months. I wanted to keep tabs on the humidity in the house before I installed hardwood floors.

[beenthere]

You can always get a whole house dehumidifier if it doesn't emove enough moisturre.

[BigJon3475]

69% RH right now where I'm at in Charlotte, @ PTI 73*, 67% RH, 62* dew point.

Where did he get those outdoor design temps. I grew up in Greensboro and all my family is there. It's always had lots of humidity.

I see 19* for heating and 90* for cooling, coincident wet bulb is 74, 50% RH leaves you with 37 design grains, M (DR)