We bought a brand-new house in May 2002. This winter (I don't think it happened last winter) when it got really cold outside, the furnace blew cold air. When it warms up outside, it starts blowing warm again. We had someone come and look at it and he told us it had a 30 degree heat pump?? And when the temp falls below 30 degrees, the heat pump will stop working and we go to emergency mode (which causes the fan to blow and run up the electric bill). He said are only option is to buy a new unit as we can't just get another heat pump. Is this true? Please help!

The only reason for the heat pump to kick when it gets cold is if there is an outside stat on it to tell it to. Otherwise the heat pump will keep running and the backup heat (electric) will run. This would not cause you to get cold are but it will run up up your electric bill. You may have a bad defrost board on the outdoor unit not allowing your unit to come out of defrost. In any case kick the last servise guy to the curb and try another company. Good Luck.

You have been living there 7+ years. If this is something different than what you have observed in the past, then something is wrong. Follow previous advice.

3 yr old post

Yeah, but it's kind of fun... you can say whatever B.S. - give it a try!

Furnace is blowing cold air

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Originally Posted by rauberry

We bought a brand-new house in May 2002. This winter (I don't think it happened last winter) when it got really cold outside, the furnace blew cold air. When it warms up outside, it starts blowing warm again. We had someone come and look at it and he told us it had a 30 degree heat pump? And when the temp falls below 30 degrees, the heat pump will stop working and we go to emergency mode (which causes the fan to blow and run up the electric bill). He said are only option is to buy a new unit as we can't just get another heat pump. Is this true? Please help!

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Since a HEAT PUMP is simply an AC unit that mechanically reverses operation, the temperatures and pressures will be similar to what's expected if air conditioning the outdoors !
Design conditions for an AC unit is 95F outdoors, 80 F indoors, with a 125 degree condensing temp outside and 270 psi with R22 and about 69 psi and a 40 F coil inside, provinding a 20 degree temperature differential from the 80 degree air entering the unit and the 40 F coil providing a 60F supply temperature.
Consequently, the Evaporator coils in the outdoor section in heat mode, it uses the ambient temperature to evaporate "boil" "flash" the liquid refrigerant exactly as it does in AC mode, just outside. Now if the liquid refrigerants 35-40 F degrees
Only air above that temperature can provide any heat exchange, and if the air is cooler than the 40F refrigerant, it actually will "subcool' the refrigerant, ewxactly opposite of whats required, then the liquid refrigerant travels to the compressor
where it will hydrolock the compressor as liquid wont compress as vapor can and will destroy the compressors valve plate or rods etc. Rotary or scroll compressors wont lock up as reciprocating types, but still wont do anything but waste power. Unless the refrigerants both condensing and evaporating , there is no refrigeration cycle /thus heat via that mode.
This is when/why they wont run much below 40F outdoors generally, Some will but the reduced efficiency shows the temperature differential beteween mediums (air and refrigerant liquid/vapor)is minimal.
To have a heat pump run a 20 F coil in Heat mode will equate to a 20 F coil in the AC mode within reason, and that wont work , nowhere near that temp actually about 35F is as low as you dare run a coil or the condensate will ice on the coil, eventually climbing and obstructing the entire coil.
Older units required a outdoor stat or common sense for using heat strips sans compressor for the heat mode, called "emergency heat" and "aux" "2nd stage" heat modes as well depending on what sequence of operation you are in, example in defrost they are energized to temper the indoor air as its just air conditioned air while in defrost mode! We are air conditining our home to defrost the outdoor coil with refrigerant gas, tempering the supply air to resmble heat(kinda) and add btu's to the defrost cycles operation and not rob the room 100% for it all!

Electric resistive heat strips are 100% efficient in converting Watts into BTu's,
1 Watt = 3.45 BTU's.
Heat pumps are around 300% efficient in that for 1 Watt you get about 11-12 BTU's
via the refrigeration cycles "latent heat" properties.

So as the outdoor temps drop closer to the coils temperature, the coils ability to remove any heat is reduced until there is little or no heat exchange, in the correct direction that is, since as the outdoor drops further the air actually will subcool the refrigerant rather than evaporate it!