Backup Heat Source Necessary?

by **JackA** » Fri Nov 06, 2009 6:58 pm

We live in N. Virginia and are considering installing a geothermal system to replace our existing LP furnace. Is it necessary to have a backup system as we would like to get off of the LP all together? We have an LP fireplace that could be used if everything failed. We also have an electric heat pump for the upstairs of the home that will remain until it dies. Any advice would really be appreciated.

by **waterpirate** » Sat Nov 07, 2009 4:11 am

Hi and welcome,
Most building codes require the installation of emergancy(electric resistance) heat as part of the heat pump install. Wheather you ever use it or not is a subject for the design phase of your project.
To answer your question directly no. The seperate system upstairs as well as an lp fireplace will be more than enough.

by **teetech** » Sat Nov 07, 2009 6:14 am

You should not oversize your unit to handle 100% of your heating load. If the fireplace will carry you through the coldest days that would be fine. As waterpirate said you would not have to use electric heat if you don,t want to.

by **palacegeo** » Sat Nov 07, 2009 8:10 am

waterpirate wrote:Most building codes require the installation of emergancy(electric resistance) heat as part of the heat pump install.

I have never heard of code requiring back up. Not saying it isn't so, just surprised.

Any body else run into this?

by **gabby** » Sat Nov 07, 2009 9:36 am

Local building codes take precedence over state and federal minimum requirements; therefore, "who knows what lurks in the mind's of men."

by **urthbuoy** » Sat Nov 07, 2009 10:11 am

I would ignorantly suggest that any codes such as that may be referring to air source heat pumps?

by **JackA** » Sat Nov 07, 2009 10:24 am

I failed to mention that the reason for the LP backup is that my 200amp panel is very close to being maxed out and therefore they quoted me an LP backup so as not have to upgrade my panel ($$$) to handle electric backup.

by **ciws14** » Sat Nov 07, 2009 11:38 am

You should not oversize your unit to handle 100% of your heating load. If the fireplace will carry you through the coldest days that would be fine. As waterpirate said you would not have to use electric heat if you don,t want to.

Really? How about 95%?

by **gabby** » Sat Nov 07, 2009 1:10 pm

I don't believe any heat dominated region would have an aux heat source. I know I can't find anything in Texas code, and I heard Florida has no such requirement.
Ohio has no such requirement that I am aware of since long before heat pumps, all electric homes had only one source of heat. Now that doesn't mean that an all electric resistance furnace didn't have a fireplace in the structure, but mostly a choice of whomever was building the structure.

It is common to design homes with a 95% load for cooling or heating, which is based on what region one lives. My design is 97% for cooling and the heating is whatever it happens to be since heat is really not a big deal for Houston. It is not uncommon to design for 99% cooling for Dallas homes since they may have 20-40 days of 100+ temperatures with high humidity. Houston is normally designed for 75-77 degrees as an upper limit. My design is 73 degrees for both winter and summer. I don't like heat. Here the design is met with a unit that has higher outputs in stage two compared to other brands, plus it has an extra coax for dehumidifying which gives a little extra without jumping another ton. It is all about balance. I believe that the unit will run in stage 1 about 70% of the time until the temperature breaks 93 degrees, then it is stage two. Winter operation should never move into stage two unless it snows at the Alamo.

by **gabby** » Sat Nov 07, 2009 1:23 pm

Your electric load would change if you got one or two Geos to handle both loads. Removing the air source heat pump may be all that is required, or switching to a single source heat source zoned for the two loads.
In either case a load assessment would need to be taken prior to choosing which route to pursue.