I am trying to size a geo system and I did the heat gain and heat loss on Heatload .com,now Here's my Question.The total loss is 42213 btu and the gain is 37173,but I have Two rooms that can be shut off and are only used occasionally and they account for 18000 btu loss and 16000 btu gain by themselves.One room was converted from a back porch to a sun room off the living room
and I left the double pane french exterior doors in to isolate it,the other room is a bonus room over the garage and the only second floor room.It is still unfinished but planned to be used as a craft room  and exercise area.Both rooms would not be used in extreme cold or heat .Do i need to size for them all the time use or do I size without them?Thanks for any advice

That's up to you. If you really don't plan on using them, you can decide to undersize the system. I'd still recommend against this, though. Your preferences in the future may change, and then change the use of those rooms. Also, you may for some reason sell the house. It will be a higher install cost up front, but to add another heat pump in the future for those rooms would be far more costly.

Davar,

Most of the loss or gain values from software packages buffer to oversizing the system. Along with most contractors will lean to oversizing as well. You can't blame them. Having a customer come back with complaints of not enough heat could be a a real issue.

I took a different approach when sizing my system. I purposely undersized it. Some people would question this move. I wanted to have my unit hit 100% duty cycle once the outside temp dipped below 10° F. My system was put into service as of last Christmas. Here in Michigan we've had some very cold temps the past few months. I missed the mark by 5°F. My system will run full time at about 15°F outside temp. The advantage to this is cost of the unit up front, and a lower current draw then a larger unit. I keep our whole home at 71°F, and it will hold this temp down to about 5°F. At this point anything lower outside the inside temp will loose ground. At -5°F the inside temp will drop to 65°F. I have backup propane furnace and fireplace if I need it, but the 65°F is still warmer then what we would keep the house when we just had propane heating system. So, for the few days we get extreme cold weather, we are willing to deal with it to save year round with a undersized unit. I'm heating 2270 sq ft of first and second level plus another 1450 sq ft of basement with a 3.5 ton single stage unit. One other advantage, my unit also has a desuperheater for the domestic hot water supply. This type of heater can only add heat when the main system is running. By having a higher duty cycle there is more time to take advantage of the desuperheater. The choice is yours.

Regards,

Eric D

Davar,
Do you have a well or horizontal ground setup? How much did this add to your electric bill in KWH? I'm up here in Maine and I'm in the process of seeing what is best for our area.

Hey Eric,

Welcome to the forums.  These guys even allow sig lines.

 I think Topgas wanted to direct his question to you.

Eric,

What kind of cooling needs do you have in Michigan?

Hi Dewayne!

Thanks for the welcome! This website looks like it has a lot of great topics and people! Yep, I got to get a sig line made up..

Where I’m located we will see outside temps at times in the upper 90s during the summer. My home had a central A/C of 4 ton capacity. This was more capacity then was needed. On cooler days the unit would short cycle. The second level stayed hot and the lower level would be too cool. Running the blower fan would help, but the system was very noisy and leaving the fan run all the time was annoying.

I have not used the geothermal for cooling yet, other then to test it. I’m patiently waiting for the type of weather that I can try the geo for home cooling. I’m confident this system will work very well. I’m hoping for longer duty cycle times to take advantage of the desuperheater.

During the installation of this unit I redesigned the supply and discharge plenum with internal sound insulation. This makes for an extremely quiet unit. You can barely hear when the fan is on.

Eric D