What location?

How old is your system?

3 tons for 3 K sq ft seems light.

TD

HVAC is not my trade. We know so little about your location or the construction details of your house. In my opinion, the strip heat should be in the range of 30 to 36 Kw. That would provide satisfactory heat in most situations in the event of the failure of the heat pump.

Depends on location and while I don't like to disagree, 30-36 KW is not correct.

Each KW of heat strip size yields around 3400 BTUs of heat.

IMO

Posted by tigerdunes (My Page) on Thu, Jan 29, 15 at 19:37
What location?
How old is your system?

3 tons for 3 K sq ft seems light.

TD

Central VA.
Usually 40's in Winter months with maybe 3-5 days of sub Freezing.
Trane XR17 + TAM8 air handler almost 2 years old.

House was certified to be about 50% tighter than average house.

We're by no means cold but when HP goes into defrost & Aux heat kicks in - certainly is NOT warm coming out of the vents.

This post was edited by pbx2 on Fri, Jan 30, 15 at 16:55

for pbx

You need a 10 KW heat strip minimum if only to properly temper the air on a defrost call. Any secondary heating source for your home other than your HP system?

A 10 KW heat strip would give you an additional 6.8 KBTUs.

You have a very nice system and obviously well insulated and tight home.

TD

Heat strips should be properly sized to fully heat your home at winter design conditions for your area in case of compressor lockout or failure, not just for defrost mode. They should also be staged.

The elements alone are not that expensive to go from say 15kW to 20kW. However, you cannot go much larger than that as itâÂÂs likely unnecessary and much larger than than 20kW would require a 400amp entrance that would be quite expensive to install if not already in place, particularly if you were to use copper wire.

IMO

SR

"So how much should i be prepared to pay to get it up or over 10KW?"

Around $300.
How do you know what the strip heat rating is?
How do you know or what makes you think stip heat is working at full capacity?
You didn't ask but I think it is more likly to be somthing other than undersized strip heat. As I recall,your air handler has multiple heat strips which are controled according to recent history stored in a logic board. Depending on program,the control turns on one,two or more strips to satisfy command. If you desire more heat from strip heat,the system can be reprogramed to bring in another strip or two during defrost.. Check your user manual for instructions or ask the tech who does annual maintainance to reprogram it while he's there.
Contrary to common beliefs,air handlers may be shipped with too many or to few elements for climate where it winds up being installed. Compitent installers disconnect existing elements or sell and install additional elements to size unit to climate. Anyhow,there's the short answer you asked for plus the one I believe will actually help you with your complaint about lack of warm air during defrost.

I agree about the pricing.

2 things you need to know though.

Dealer undersized you on the heat strip. He should exchange this at no charge.

and second, he speced a TAM8 air handler which costs more, should have been the TAM7 which would be correct for a non communicating HP condenser.

IMO

Posted by tigerdunes (My Page) on Fri, Jan 30, 15 at 18:59
for pbx
You need a 10 KW heat strip minimum if only to properly temper the air on a defrost call. Any secondary heating source for your home other than your HP system?

A 10 KW heat strip would give you an additional 6.8 KBTUs.

You have a very nice system and obviously well insulated and tight home.

TD

Thanks for the constant feedback over the years as I couldn't have build my HVAC system up without some of your advice!

Anyhow, we also have a 36000 BTU gas fireplace that supplements our open floor plan in the main common areas.

This generates a lot of good heat for this area & as a byproduct warms the upstairs well too.

I've Googled Trane's heat strips & saw that they have a 7KW/12KW 2 stage electric heater that seem interesting. Not sure if this would be a better balance for Central VA's very moderate weather.

Posted by fsq4cw (My Page) on Sat, Jan 31, 15 at 0:30
Heat strips should be properly sized to fully heat your home at winter designconditions for your area in case of compressor lockout or failure, not just for defrost mode. They should also be staged.

SR

Thanks for the feedback SR.

I recalled that while they were designing my house, the installer sent me an email referencing a 37* design temp.
Not sure if that had anything to do with my 8KW electric strip vs. the entire envelope calc.

I do see on my Trane T-Stat the W1/W2 connection's historical data as being recorded but I am not sure if that means the heat strip is staged x2 or is symptomatic of the defrost running??

A 37 degree winter design temperature is wrong for a Northern Va location. Don't understand what dealer was thinking. That leaves me to believe your system may not be sized correctly but that's another issue in itself. I would hope dealer was not including your gas fireplace unless you told him too. Certainly the gas fireplace won't help you in cooling this summer.

The two stage 7/12 KW Trane heat strip would be an excellent choice.

IMO

Posted by tigerdunes (My Page) on Mon, Feb 2, 15 at 12:54
A 37 degree winter design temperature is wrong for a Northern Va location. Don't understand what dealer was thinking. That leaves me to believe your system may not be sized correctly but that's another issue in itself. I would hope dealer was not including your gas fireplace unless you told him too. Certainly the gas fireplace won't help you in cooling this summer.
The two stage 7/12 KW Trane heat strip would be an excellent choice.

IMO

Just to clarify - it's Central VA & the temps here during winter are usually mid 40's on average for Dec-Feb.

That said re: sizing - I will ask him to revisit this & see if we can get some more heaters in there.

Thanks TD, Klem, & SR!

Pbx2

Plain and simple, that 37 degree design temp is wrong.

I am also worried for you this coming summer as far as cooling.

If this was my new home and system, I would want to see the load calc both heating and cooling in writing and the design temps used for cooling. Should be 93 outside, 74 inside with humidity 40-45 RH. It will be interesting to see what your dealer used.

TD