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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a hvac question. I need help sizing a furnace and a/c

Customer Question

i have a hvac question. I need help sizing a furnace and a/c unit.
Submitted: 1 year ago.
Category: HVAC
Expert:  HVAC Guru replied 1 year ago.

Hello and thanks for using this service, if you have been waiting do not worry or get upset. I am GURU an extremely experienced tech on here and I try to get to as many customers as I can. I just picked up your question now.

Please allow time for me to respond, sometimes I get the questions or responses late so please be patient as I have no control over the site issues. NOTE, I have nothing to do with your payment to the site and personally did not receive that money. The only way I am credited is when you use the STAR/VOTE RATING SYSTEM at the top of your page. Lastly when we are done please post to me that you would like me "GURU" credited before supply the rating so there is no confusion on the tech to be credited for the question. Thank you!

What size house and where do you live?

Customer: replied 1 year ago.
the mechanical engineer selected the following specifications:4800 square feet house
R 13 insulation in walls
R 38 insulation in ceilling
Southern part of the house is covered completely by a porch ( 5 ft wide)
External static pressure is .7 iwc
Total effective length is 450 ft ( return + supply + equivalent length of fittings)
I calculated the Available static pressure as follows:
0.7 (external static pressure) -(.03( supply grille pressure drop ) + 0.03( return grille pressure drop)+).10( filter pressure drop)+ .26
( wet coil pressure drop)=.28 iwcLocation is sacramento, californiaI would like to size a goodman furnace and ac unit and coil. Please see the specification in the attachment.
Expert:  Phil replied 1 year ago.

Hello, there are many issues here.

Your engineers specs did not provide for any zoning or dual system options, those can save you 30% or more on fuel bills. The house has to be seen in order to do those calculations correctly. I can't see it from here.

The other is that your offer covers a simple answer, not any sort of complex involvement. If i take this on I will spend 4 or 5 hours on it... this job deserves more than a quickie 'answer'

You have several options:

The best quality HVAC contractors in Sacramento will provide very high quality engineering for you, and very specifically include a range of zoning options... at no charge to you.... however these will not be the low bidders.

Your other option is pay me for my time, I will submit a premium services offer if you wish for $200... for that I will provide a quite workable conceptual design that any HVAC contractor can work with.... very pointedly however it will entirely lack any and all hair split calculations on external static pressure (because a zoned system operates will below those pressure drop levels, insuring optimal performance.)

Let me know, we can go from there if you wish or you can ask me to opt out.

Customer: replied 1 year ago.
Phil , please tell me more about your offer. I have some questions:
1). What the plans would include ? For instance ,would they include any zoning dampers location / specifications.Duct sizing?
2). Could your design be made to save energy or for comfort? My primary concern is energy savings.
3). Could you provide me your e-mail adress for contact information?
4). I would prefer a 2 stage Goodman unit (Ac and furnace), if possible. Modulating units tend to be more expensive.
Expert:  Phil replied 1 year ago.

Hello again,

1. I can show the location of the zoning dampers... and depending on

how involved you want to get with premium service options, duct layout and sizing etc.

2. Energy savings is the primary benefit with zoning. Depending on which

option you choose the size of the equipment can be a bit smaller with

a zoned system.

3. The company only allows direct contact with phone and email if the

customer pays for at least one premium service.

4. I prefer the various non modulating systems. Both first cost and

repair costs are reduced that way. Modulating is quieter, however.

5. In your case it is most likely you will end up preferring, two smaller

zoned systems. allowing you back up when one of the inevitably fails,

and more fine tuning of the load saving maybe as much as 50% on

utility costs, and being much easier to diagnose and repair.

Goodman is very decent equipment in my view, the dealers though

do not have to meet franchise requirements, so the install quality can

be a problem unless the dealer is properly vetted. There are many

other options as well.

Let me know, we can go from there.