Central AC Retrofit. Hack or Not

[dave72370]

So I was talking to my Parents and they told me they we having central AC put in. Their house is a tri-level house. For those who dont know this style, it is basically a Y turned sideways with the bedrooms on the upperlever with a full finished basement below, and the main floor as the stem on the Y with a 3.5 foot enclosed crawl space with dirt floor below it.

Right now it has a warm air furnace (located in the crawl space) with large vents in the finished basement and smaller vents on the mail and bedroom level.

Because this is warm air only, none of the ducts were insulated.

This house is in Massachusetts

So here is what was proposed.

Install a 3.5 Ton 10SEER Armstrong condesor with an A coil in the return. Also a condensate pump. Thats it

So I told my parents this does not sound right

I told him to ask if a load calc was done.

What about condensate on the duct work??? Mold??

How will they balance airflow so that the temp will be relatively even.

The hvac guy mentioned that he could put in a dehumidifyer in the basement to control the ductwork sweating


Thanks

[sean88]

Not knowing the sqft of the house it's hard to say if 3.5 tons in the right size or not.

Also, what is the size and configuration of the AHU? Horizontal I assume since it's in a crawl space. It's good practice on a retro fit like this to put the coil in the supply after the heat exchanger there is the risk that moisture will blow off the coil onto the heat exchanger and rust it. Are the ducts in the crawl space insulated? If not they should be. Since the ductwork in the basement is in conditioned space you really don't need insulation. It's similar to exposed duct you see in large grocery stores.

Do the supply registers have dampers in them or are there dampers at the branch ducts? That's how you balance the system.

[dave72370]

You are correct this is a horizontal unit. The hvac co is planning on putting the coil in the return size. Also the registers are able to be closed. However there are no zone zone dampners anywhere in the branch or trunk lines

the house is about 2300 sq feet. Build in 1970 with all brand new windows.

Also, the crawl space although it is enclosed it is not conditioned. And like I mentioned before it has a dirt floor

[dnt]

Duct in all unconditioned areas will need insulation, it will be hard to keep the duct from sweating and still receive adequate cooling. Controls can be added to read dew points that can control the air temp inside the duct (add outside air or shut the compressor down) but there will be times when the vent temps will be very high and very little cooling since the compressor will be shut down or a large amount of outside air is being added, and this will happen when you most need cooling. Are the duct lines not acessible so that insulation could be added? If left to shoot cold air thru the uninsulated duct at will, this AC unit (if charged correctly and under moderate to high temp/humidity conditions) will sweat the metal ductwork a whole bunch in the unconditioned areas, you are right to be concerned.

[Edited by dnt on 05-16-2005 at 11:36 AM]

[Steve Wiggins]

dave the problem here is you are looking for skilled design work for free. If you want something designed to work right then you need to pay for it. 99% of the time there is no design and the customer gets screwed by buying something that is doomed from the start because of their own cheapskate behaviors.

[Shophound]

A few items of concern:

Definitely get a Manual J heat load done. Rules of thumb based upon square footage are not the way to go for best results.

Present air handler/furnace may not have enough CFM capacity to move sufficient air across cooling coil. Also, if age of furnace is advanced, it would be better to replace at same time cooling equipment is being installed.

Any ductwork that will move cooled air should be insulated. Even possible for ductwork passing through chases in house to reach upper floors to sweat if conditions are right.

Cooling coil should not go on return side of furnace.

Ductwork should be assessed to determine if it has sufficient capacity to move higher CFM's of more dense, colder air. If it was sized for heating only, it may be undersized for cooling requirements.

Get more than one bid!

[chillbilly]

Originally posted by Steve Wiggins
dave the problem here is you are looking for skilled design work for free. If you want something designed to work right then you need to pay for it. 99% of the time there is no design and the customer gets screwed by buying something that is doomed from the start because of their own cheapskate behaviors.

Don't you think that's a little harsh Steve?
An uninformed customer is different from a "cheapskate".
Dave wants advice and seems willing to do what is needed to correct any problems.
Why the cheapskate label?

Dave;
Insulated ductwork is needed.
A load calculation is also needed.
Correct duct sizing should be verified and equipment can be sized after load considerations.

[Steve Wiggins]

I am taking all my past frustrations out on dave. I think he can handle it, he seems pretty level headed.

[dave72370]

Back off Steve !!!!! Nah just kidding :-)

You have to understand I was at my Parents Saturday and this is what my mother showed me. She does not know any thing about this. Well the HVAC guy should know what he is doing right? Is what I was told.
To make matters worse she also payed this guy his 50% down. I just want to make sure they get the best systems without having problems very quickly down the road.

DAve

[thunderglass]

Get that money back now. Step up to the plate and do this for your mom. Paying 50% up front is always a red flag in my book. Any good company will only ask for payment after the install is finished and all is working. Do get more bids. Good luck.

[Twilly]

Originally posted by thunderglass
Get that money back now. Step up to the plate and do this for your mom. Paying 50% up front is always a red flag in my book. Any good company will only ask for payment after the install is finished and all is working. Do get more bids. Good luck.

We often ask for a down payment, even 50%, you have to trust the customer to pay you, why can't they trust you to do the job?

Also cuts down on buyers remorse. Keeps you from putting them on your schedule and ordering special equipment and getting out to their home and finding out they changed their mind.

Down payment doesn't equal dishonesty.

[beenthere]

we always get a down before we start, some times the day we start, some times when we close the sale.

I thought it was standard procedure.

[beenthere]

Oh, and what chilly said.

[tinknocker service tech]

dave
the down seems a little high but that may just be the way it is with that co. as far as the duct it needs to be insulated. the coil should be in front of the furnace not in the return. if the furnace is farely new the warrenti on the heatexchanger will be voided if old then it may be time to replace the furnace anyway. call the contractor and find out what he plans to do and let him know what you want for your parents. make sure they do the job right
but be careful not to ofend your parents at the same time

[dave_slo]

GET THE MONEY BACK I will say it again in case you didn't hear me...GET THE MONEY BACK.

Even if it is impossible, or you have to take the guy to court, don't use him. It sounds like he is proposing a hack install. Better to lose a little now, than a lot later, as you will have bought a piece of cr**, and will have to spend thousands more to have it torn out, and the damaged its going to cause repaired, and a new one put in.

How old is the furnace? 35 years if its original to the house, may want to seriously consider changing it.

Uninsulated duct work in unconditoned space, you are losing a lot of heat, and will lose a lot of cool to that crawl space.

The guy wants to try and band aid the duct sweating by putting in a dehumidifier? Man I would have my Nikes on and you would be seeing my dust as a got away from him.

You need to get some reputable people in to look at what you are going to need. Its not going to be cheap, but then again you will not have mold growing in your crawl space.

[allan38]

The old ductwork will be undersized for Air Conditioning. You'll need approximatly 400CFM airflow per ton of AC. Thus the 4 AC Ton unit will need 1600CFM of airflow, a lot more than the old furnace only system. You may be able to shove that much air through the old ducts but they'll be noisy.
The unisulated ducts in unconditioned space will sweat, and while sweating lose cooling capacity from the system. Also make sure they size the controls transformer for both loads. They'll either need to put in a larger 24V transformer or put another one in the system ( and make sure the 2nd one is in phase with the new one)
Properly designed it's not a big deal, Just retrofitting in an A-coil and condenser to a previous furnace only system is a trainwreck waiting to happen.

Allan in Austin.
Still looking for work.