Heat and Air Duct Advise

OKnewguy · Oct 10, 2011

Hey gang, we have a apartment that is attached to the back of our garage. I got some quotes for central heat and air for the place and was blown away at the cost! The place is 792sf measured on the outside. The walls are cinder block with a layer of 1" layer of foam board and then sheet-rock. We currently have window units and electric baseboard heat. Our current tenant is elderly and the cost to heat is crazy! I have gotten quotes between $7800 and $8700 to put in split central heat and air(gas heat). Another contractor said that there is not enough space in the attic to go with a split system and wants to put in a packaged unit. I had looked at the packaged units before and did not really like them because they are so large, but these prices are making me wonder if I should put one in myself. They do not require messing with the refrigerant because they are self contained outside.
My big question is the duct sizing. What do you guys think of this plan? Most of the register are 6x10" and are feed by 6" duct. The main feed is 16" and then reduces down to 14" and then reduces down to 10" for the last room.
I believe I can save between 3 and 4 thousand dollars by doing this myself.
Any help/comments are much appreciated.
Thanks, Dave

Ken · Oct 10, 2011

I would think a contained unit with proper return and then flexable duct to rooms. Length of less then 20 foot each. all could be done by yourself.
Don't go to small on the return unless the sound of a jet plane isn't a problem.
We just installed 2 contained units in a church fellowship area 40' by 80' and 16' high. return duct of about 4 feet length and the 24" square for filter. The cold air about 8' up the wall then register to direct the flow. Soon found out the 2nd unit could be shut off soon after starting . admazing how quickly the room cooled.
With your rooms of approximate 40X20 ' total
Go to a a/c supply and discuss with them the need usually willing to help in a plan.
Labor is the prime expense in installatioins.
ken

CurlyDave · Oct 10, 2011

OKnewguy said:
...Our current tenant is elderly and the cost to heat is crazy! ...

I have no doubt that you can save about 50% of the cost by doing the installation yourself.

However, as a long-time owner of rental units, I see two problems:

1. Doing almost any major work on a rented unit, with a tenant in it, as a do-it-yourself project is just not feasible. You are going to disrupt the tenant's use of the space for a long time, the tenant will probably object, and he will be right. A contractor is going to be in and out in a few days. Unless you have a very experienced helper, you are going to take a lot longer.

2. If you allow the tenant(s) to see the work in progress, that work will be inspected every day by the tenant and you may be accused of cutting corners and not doing a good job on the install.

Unless the tenant is a relative, I would wait until the apartment is vacant and do the work before re-renting it.

Also, I would consider the total costs of a d-i-y install over a contracted one. With a rented unit, there will be both loss of rental income and loss of tax benefits, to throw into the equation.

With the economy the way it is, you can probably find an independent installer willing to work for a lot less than a heating business. This may well be the the overall lowest cost solution.

OKnewguy · Oct 10, 2011

Curly, the tenant is a relative (my mom) she moved out here after dad passed away about a year ago. This is inherently part of the problem. We have always rented to college kids ( the University of Central Ok is close) and they would keep the place reasonable in the winter. Now that my mom moved in she keeps the place about 80 to 82 all the time. This works out great in the summer, but caused our electric bill to be outrageous last winter.
Anyway, she is very understanding, and will not have a problem with me doing the work.
Dave

OKnewguy · Oct 10, 2011

Oh by the way, the house is about 44' by 18' measured on the outside. The farthest room will be a bit away, especially considering going up the wall and then across the attic.
Please let me know if I can answer any questions, I will check this thread many times tonight.
All help is appreciated
Dave

OKnewguy · Oct 10, 2011

Your idea about going to an a/c supply place is good. Thanks Ken

hizoot · Oct 10, 2011

I've been doing HVAC for 34 years now....

all this to say...in all that time I can remember maybe 2 guys I would trust with duct design. Some can help on equipment selection as they have had seminars etc put on by different manufacturers. But still...its kind of like going to Pep Boys and getting mechanical advise. If you PM me I'll do my best to help you out

Sigarms · Oct 10, 2011

ANY duct design is useless without a proper load calculation.

OKnewguy · Oct 10, 2011

What does a load calculation involve? This is just a 800sf building, can it really be this difficult?
Help
DAve

kenmac · Oct 10, 2011

OKnewguy said:
What does a load calculation involve? This is just a 800sf building, can it really be this difficult?
Help
DAve

Not that difficlut but, it's not plug & play either. Load calc, cfm, flex vs metal, etc,etc,.All of this is usually taken into consideration. It Just depends on how well you want it to work. Usually, you would know CFM'S friction rate , etc,etc, to size the duct work