Help - HVAC Sizing Issue and Variable Speed?

ojs2005

17 years ago

Can you tell me if this sounds right -- i have a large victorian -- about 1800 sq ft per floor with 3 floors (not including basement). We have very large 1 pane windows and the house is not insulated (we will probably insulate this year, but the windows are another story). My contractor's HVAC person has recommended installing Rheem equipment -4 ton condensers and 4 tons coils (13 SEER) with 5 ton drives for the AC, and 100,000 BTU furnaces -- for EACH floor. which would mean i have 12 tons of cooling in my house. we plan on putting a couple of ducts to the basement for cooling purposes but it has separate heating and we don't want to spend much money in the basement right now. They are telling me that this is the right size and not to spend more on variable speed higher efficiency units.

This is around the range of what other people offered, some thought more tonage, some thought less. One ocntracter suggested 3, 3.5 and 4 ton units for each floor respectively and said this was based on J Manual calculation. They also suggested about 85,000 BTU heating per floor -- but their price was almost double so I wouldn't even consider using them.

This is making my head spin. Does this sound right? Does it really make a big difference to have variable speed units (which I was told would cost about $12,000 more than our current quote to install in order to upgrade all the equipment and additional labor costs)?

I just don't want to spend all this money and have a house that's not comfortable because the A/C is oversized or uncomfortable.

Any thoughts would be MOST appreciated.

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Comments (7)

ryanhughes
17 years ago
"They are telling me that this is the right size and not to spend more on variable speed higher efficiency units."

I would avoid this dealer at all costs. I am very skeptical of their sizing methods and their turning you away from better units.

You are getting "Rheemed" with your upgrade costs as well. It likely doesn't cost them a good fraction of that to go to the better units. Not sure why there would be additional labor involved either.

You would do yourself well to have another couple quotes. Ask on the phone before they come out about their sizing procedures. You will save your time and theirs.

It may be that your home needs that much heating and cooling, but I really would be skeptical without proof. Can your ductwork handle the amount of airflow needed for the units is one question. Is the home not insulated or lots of windows?
srercrcr
17 years ago
I'd like to know where this is to better understand heat and humidity conditions.
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ojs2005
Original Author
17 years ago
Thanks for the responses -- much appreciated. I'm in NJ in Essex County.
srercrcr
17 years ago
My knowledge is it gets hot and muggy in NJ so I would be concerned about being sized properly. Like someone said, if its too large it will have short runtimes and not wring out the moisture. Variable speed will give the opportunity to install a hunidistat....

A humidistat only costs maybe $100 for the part. Check with your contractor to verify but with mine.....I set it to a certain humidity % and as long as it is wetter than that inside.. the unit will automatically run at slow speed to extend the runtime before reaching the desired thermostat temp setting. You need a variable speed blower to do this. Works good in the morning when the unit may not go on cause there's little heat load but humidity is 85% outside. You have to play with it, cause if you have it set too low, it'll never shift up to high speed. During the hot day you want it running high speed for max cooling, and it will cycle enough that the air will dry out.

The problem is you've got ahuge house with no insulation and inefficient windows, that certainly leans toward a large system, but 12 tons is huge. Ducting is very labor intensive too.

It's a tough decision, hopefully I've given you SOME insight.
veesubotee
17 years ago
You would do well to reduce your heating and cooling loads before thinking about upgrading/replacing equipment.

Doing it later will change (lower) your requirements resulting in having oversized equipment. Net result: higher costs, much less degree of comfort due to short cycling.

I would also be concerned about whether your duct system could handle the larger equipment.

V
ojs2005
Original Author
17 years ago
Thanks everybody -- we actually have no A/c or forced air currently so we're scrapping our radiator heat and ducting a new heat/a/c system now, so the ducts will be made for the system installed. It's all pretty overwhelming and confusing for somebody that's a first time homeowner!
veesubotee
17 years ago
"Thanks everybody -- we actually have no A/c or forced air currently so we're scrapping our radiator heat and ducting a new heat/a/c system now, so the ducts will be made for the system installed. It's all pretty overwhelming and confusing for somebody that's a first time homeowner!

The ductwork will be 'made' for this system, but unless the system is properly sized (Man J), and the duct system designed per Manual D, you may not be happy.

V