Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
Does the house now have central heat&air and you're upgrading? Or is this a new install in a house that has no central heat&air (currently using baseboard heat or steam)?
Just for general info.
Either way, I would approach it like this.
Have a Manual J calculation done on the house [Manual J8ae(8th Abridged Edition)]. If the current contractor doesn't have one and made his "calculation" without one- move on to the next contractor.
From that you can determine an annual cost versus SEER rating. From there you can determine which is more efficient (1 or 2 units) versus the install cost. The other consideration (if one unit is used)- how to run duct work from one floor to the other. Rarely is there an existing chase to accomplish this task- which means a loss of closet space, ceiling height, or floor space. In that particular scenario- if a loss of space is not up for negotiations- then 2 units maybe the way to go.
Insist upon a Manual J calculation and look it over to see if all the tangibles were used the the calc'.
determine an annual cost versus SEER rating. From there you can determine
Insist upon a Manual J calculation and look it over to see if all the tangibles were used the the calc'.
The installer calculated the sq footage of all rooms, with a tape measure. I am not sure if a manual J calc is something different? You bring up some great points about the closets, etc, with 2 systems.
We currently have baseboard heating, to answer you question. All ducts, etc, would be new.
Hi Glad,
The concept you want to consider is this: moving air is being used to control the system and therefore your indoor air temperature. Proper communication of the air going in and out is essential!
One system, adequately sized is sufficient if:
1) You have a thermostat at a common area( such as a hall) on each level.
2) You have an adequately sized return air inlet with a filter NEAR a thermostat at a common area( such as a hall) on each level.
3) The duct baffling system is readily accessible in case service is required.
That is a basic level/floor controlled system and they work well!
Do you mean one thermostat on each floor, even if it's one zone and one unit? The installer did discuss the return and theromostat going in a central area, like the stairway. But only one thermostat. Do you actually mean two, one on each floor?
Hi Glad,
Yes I mean one thermostat each floor, and one return air on each floor; near the thermostat. The thermostat is what analyzes the temperature of the air. Each floor of the house will have to be conditioned slightly differently to maximized efficiency and effectiveness. Each thermostat will make decisions about how much hot or cold air the space it is serving requires to achieve the temperature you set it at. The ducting baffles will respond to the command of the thermostat(s) via a mother board in the forced air unit. The extra thermostat and wiring, the baffle system and the additional return air inlet will cost more, but it will make your system much for efficient, the occupants of the home more comfortable, and it will be much less expensive than installing two systems! Barking spider's post was right on the mark about how this can be an issue.
Hi Glad,
Yes I mean one thermostat each floor, and one return air on each floor; near the thermostat. The thermostat is what analyzes the temperature of the air. Each floor of the house will have to be conditioned slightly differently to maximized efficiency and effectiveness. Each thermostat will make decisions about how much hot or cold air the space it is serving requires to achieve the temperature you set it at. The ducting baffles will respond to the command of the thermostat(s) via a mother board in the forced air unit. The extra thermostat and wiring, the baffle system and the additional return air inlet will cost more, but it will make your system much for efficient, the occupants of the home more comfortable, and it will be much less expensive than installing two systems! Barking spider's post was right on the mark about how this can be an issue.
Thank you. So they can install 2 theromstats on one zone? If so, do they need to be set at the same temperature? Or can they be set at different temps? What do you think of the return and thermostat being placed in a semi common area, such as the stairs going up to the second floor?
Hi Glad,
Each floor will be considered a separate zone; you will have two zones and one thermostat for each zone; each thermostat can be set to what ever temp you wish, however, it must be in the same mode i.e. the upstairs cannot have the furnace on while the downstairs has the AC on. Some manufacturers allow the common return air concept you elude to;bring that up to your installer and see what they say; it is better to have two return airs ,but, if you only have one; make sure is adequately sized all the way to the back of the return air plenum.
The installer calculated the sq footage of all rooms, with a tape measure.
Well, I can assure you that sq/ft or ft3 is not all the calculating that is done. It involves a rather lengthy list-
An MJ8 produces equipment sizing loads for single-family-detached homes, small multi-unit structures, condominiums, town houses and manufactured homes.
MJ8 also accommodates homes that have exceptional architectural features and life style accessories such as:
Dwellings that have limited exposure or no exposure diversity. Homes with large south-facing glass area or rooms with unusually large glass area.
MJ8 is sensitive to an increased variety of issues related to construction materials and methods including:
Fenestration loads for glass rated by the National Fenestration Rating Council (NFRC). Improved duct load models. Improved methods for estimating the effect of internal and external shading devices, including insect screens. Infiltration estimated based on blower door test. Sensitivity to latitude and altitude. Sensitivity to skylight glazing material, curb construction and light shaft construction- if any are present. Heat gain sensitivity to roofing material, roof color and the use of radiant barrier. Heat loss and gain for log walls, structural foam panels, aerated autoclaved concrete block, insulated form concrete panels, brick walls, concrete walls, wood foundation walls, and any other types of walls and insulation options.
These are all items that can determine how a house operates as a system. And that calculation can best determine the size for a particular dwelling. Sq/ft and number of rooms are things of the past! Any contractor who wishes to stay in business in the near future will either learn how to use a manual J or will have to hire someone who knows how. Especially with many convening authorities (C/A) now requiring a manual J calculation with a permit application. Just like the impervious calculation (it's to determine the amount of runoff from a lot) that has to be done per/lot with a lot of C/A's.
Please register to post and access all features of our very popular forum. It is free and quick. Over $68,000 in prizes has already been given out to active posters on our forum. Additional giveaways are planned.
Detailed information about all U.S. cities, counties, and zip codes on our site: City-data.com.
Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
