Heating systems for new home

[John Mercier]

Why would the geo be affected by ambient air temperature?
Is it not sized large enough to meet the BTU requirements of the space?

[Winilyme]

Originally Posted by John Mercier

Why would the geo be affected by ambient air temperature?
Is it not sized large enough to meet the BTU requirements of the space?

A 5 ton unit is sized appropriately for our home except perhaps on a rare night when the temp gets down to - maybe 10 below??? As that almost never happens in SE CT, we’d be throwing money away if we bought any larger unit. More cost effective to just use the electric for those few hours of unusually cold temps. Not sure I answered the question but I’m not an HVAC engineer.

[John Mercier]

You did.
They sized it for a nominal.

I would think the efficiency improvement might come from some improved insulation or a back-up that runs on that rare occasion.


I notice mine kick lower than my friend's when I went to R60 in the attic, and triple pane windows. I have a couple more items that I can do... but not sure the savings when the amount used for heating is as low as I have.

[DickR]

Referring back to my earlier post (#14) on this thread, to give you an idea of the impact of making the house in the "superinsulated" class, consider what we have. The gross conditioned space is about 4,000 sqft (two levels on a 2K footprint). The heating system is a 2-ton geo unit, and even when it dips below zero (like last week when it was -8F one morning), the thing is keeping the house at 70 F in just first stage, putting out about 75% of capacity.

Back in 2011, the area distributor for Climatemaster and two of their "approved installers" all proposed putting in a 5-ton unit, even though I gave them the spreadsheet showing that a 2-ton unit would suffice. I doubt they had any experience in sizing a unit for a house like this one, so they just used canned software and assumptions as to what the house was like, many of which were wrong. The only set of operating data I have that seems useful is for a period of several days when the temperature swung just a few degrees either side of zero. Apparently my calculations were a bit conservative by over 10%, which I am told is typical for such a house.

In the case of geo heat (or minisplits), the cost of the unit does depend strongly on its capacity, so proper sizing based on a really good heat loss calculation, not shortcuts, is essential. For a fired heat source, the unit installed typically is grossly oversized, even for a house built just "to code."

[mswlogo]

Originally Posted by DickR

Referring back to my earlier post (#14) on this thread, to give you an idea of the impact of making the house in the "superinsulated" class, consider what we have. The gross conditioned space is about 4,000 sqft (two levels on a 2K footprint). The heating system is a 2-ton geo unit, and even when it dips below zero (like last week when it was -8F one morning), the thing is keeping the house at 70 F in just first stage, putting out about 75% of capacity.

Back in 2011, the area distributor for Climatemaster and two of their "approved installers" all proposed putting in a 5-ton unit, even though I gave them the spreadsheet showing that a 2-ton unit would suffice. I doubt they had any experience in sizing a unit for a house like this one, so they just used canned software and assumptions as to what the house was like, many of which were wrong. The only set of operating data I have that seems useful is for a period of several days when the temperature swung just a few degrees either side of zero. Apparently my calculations were a bit conservative by over 10%, which I am told is typical for such a house.

In the case of geo heat (or minisplits), the cost of the unit does depend strongly on its capacity, so proper sizing based on a really good heat loss calculation, not shortcuts, is essential. For a fired heat source, the unit installed typically is grossly oversized, even for a house built just "to code."

Just got my first Geothermal estimate. $47K !!!

4 Ton for 2300 sq ft well insulated (2x6 construction dense foam).

My guess is a 2 or 3 ton would work and let the backup kick in when needed.