hello everyone,  in the process of buying moving to another house  and looking into  changing from propane heat to  geothermal unit and want to get up to speed on all the basic stuff to know. this is a great site and have learned a lot from reading a bunch of posts, based on the knowledge level seems like many of you are in the trade or very well informed homeowners - that is what i would like to be as well ..  so a few questions that i hope i can get pointed in the right direction

# anyone know a good link to learn more about heating load calculations?

# can i keep my propane furnace as a back up heat source?  i have talked to one geothermal installer that said no but  he did say the forced air ducting  looked adequate  for a geothermal heat pump- he estimated 3 ton system based on past propane usage for the house.   i think i have seen posts here that say the furnace can be used as backup. is there a consensus on this?

# it seems there are HVAC companies that do geothermal and there are  geothermal only  installers , most HVAC have an on call protocol for heating or cooling issues or emergencies.    do installers offer  this same type of service for emergencies etc? 

thanks in advance for any input ! john

Heat load calc info here

Using exisiting furnace for backup is a fairly common practice, with some drawbacks

the answer to your third question depends entirely on the intaller

thanks geodean,

 i probably willl not do the calucations for the house myself but plan on getting a few quotes on systems  and make sure  the load numbers are all in the same ballpark. there was some info on heating and cooling losses on the site but  i will goggle heating load and see what i come up with.

 wha are the drawbacks of propane furnace  backup?

Propane back-up systems generally cost more to operate because once the furnace fires up, the geo no longer contributes. Depending on the cost of electricity and propane, this can often mean your geo system costs more to run with propane back-up.
I have customers who go that route regardless of slightly higher operating cost <=$100/yr so that a smaller back-up generator can run the house.

With geo, you actually have 2 ways to heat your home so in a heating dominated climate like mine (mid MI) one needn't race out to a home on weekends or holidays as the house won't be freezing while the clients wait. I travel much farther for geo customers than furnace customers because of that fact.

thanks for the reply,finger lakes ny area so definetly heating dominated. what t are the two ways the geo can heat? the electric strips as the backup?

With the argument of larger electric generator needed for full strip heat backup being a valid one, it is usually much less efficient and less economical to use propane for backup. In the early days we did it if customers wanted it, but they all threw out the propane furnace soon or later. Geo is so reliable, it is not worth it to maintain the propane furnace (and sometimes the tank!). I would suggest a smaller backup element, a 10 KW makes about 35 kbtu/h, plus internal and solar gains, most of the time is plenty for suplement and good for backup. Worst case scenario, in case of a failure, the house is heated up to, lets say 65 for a day....On one of the coldest days of the year.

Regarding emergency/supplemental electric heat and generator sizing, a person could have the generator supply power to some (not all) of the electric heat coils.  This way, power is available to all of the electric heat coils while on utility power, and a portion of the electric heat coils while on generator power.

This can help keep the generator size down, but probably not as small as with a propane furnace.  That said, we chose to remove our propane furnace and use electric backup heat.  I'd make the same decision again.

thanks everyone, moving in this weekend , i probably will plan on taking out the propane furnace when the geo goes in, thinking a propane fireplace could serve as ambience and as a backup one room heat source for either power failure or geo probs if needed.

We have a 28 - 39 kBtu propane fireplace on the 1st floor (we always keep it on low.) It does a great job of heating the second floor as well. Only batteries needed on our unit and the remote. The remote has a built in thermostat, but I only use it when the fireplace is attended.