I am about to bring in a contractor to install central AC in my house. I am in the final stage of a rather comprehensive remodeling effort, all of which was done either by me directly (cca. 85%) or by closely micromanaged contractors. To explain the need for this inquiry, I will admit to being a control freak and never liking to get into any projects into which I do not have the closest insight.

Since HVAC is currently not my specialty as I have never done it, and I generally do not like to confide in contractors (albeit I admit there are some honest ones out there but I am just too much of a control freak to trust a single person without an X number of other opinions), I am looking for a testing methodology/heuristics to verify that he is doing the thing right.

The pump/condenser equipment is the easiest part and I will choose those so I am not worried about that. But the one think I am skeptical about is whether he will do a good job setting ductwork because that is specific to each case. E.g. is there an easy way (online calculator?) for me to plug in the sizes and types and angles of all the ductwork to evaluate his proposal?

Another question is whether there is some device that can measure the flow out of registers when the pump is blowing and to make sure that remote registers get proper air circulation? Also does it make sense to pump up the system (like with black pipes for gas) to make sure there is no leaks along joints anywhere in the ductwork?

Or generally, any checklist/guidelines by which to evaluate and monitor the work my contractor does.

  • What kind of heat does the house have? – wallyk Nov 26 '13 at 20:10
  • radiant heat. i like it a lot and do not plan to replace it with forced air. i also like the way my radiators fit in aesthetically (it is a rather historical property which i have made into a cross between antique and modern). – amphibient Nov 26 '13 at 20:11
  • IOW, i will use the AC system for AC only and not for heat – amphibient Nov 26 '13 at 20:12

Yes, everything you mention exists.

A blower door is used to test the entire house for leaks. Blower doors can also be used on duct systems. Airflow meters are available. Sheet metal ducts are generally sealed with a duct mastic (not duct tape!). Duct insulation is a sore point: there's nothing really great out there. Duct mastic is OK, but leaks do develop over time. Flex duct generally starts out better in terms of air leakage, but a few years down the road it may underperform hard ducts.

Most importantly, you want a system with sufficient dampers that you can 'balance' it. Unlike a typical radiant system, where you can always add a thermostat to a radiator, your options to fix any problem at the vent level are minimal.

There are tables for airflow, but the really important thing is not the absolute airflow, but ensuring the flow is nicely balanced.

Generally energy consultants do a better job of all this than HVAC contractors.

  • what is duct insulation? is it the same as sealant that is used to join two pieces together? – amphibient Nov 26 '13 at 22:43
  • Unlike a typical radiant system, you don't have individual thermostatic control in each zone -- my radiant system does not have individual thermostatic control in each room, one for the whole house – amphibient Nov 26 '13 at 22:45
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    A typical radiator based system can be retrofitted with room thermostats. I amended the answer. – Bryce Nov 26 '13 at 22:49
  • how can that be done if the water for all of them comes from a single boiler? – amphibient Nov 26 '13 at 22:51
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    we're off topic here. A two pipe radiator system you can moderate or even close individual radiators, as long as the return temperature does not rise too high. In a one pipe system you can install a thermostatic bypass on each radiator. – Bryce Nov 26 '13 at 22:55

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