I'm not an expert, just an average homeowner (who also has a Mitsubishi heat pump in Seattle), but the company should have done calculations on your home--including the windows--and installed equipment that meets the heating and cooling requirements of the house. Either the equipment isn't working right or their calculations were way off, but in either case the company needs to fix it now while there's no arguing about who needs to take care of it. On the simpler end of the spectrum, is your programmable thermostat set the way you want it for nighttime heating? Or might the heat be blowing directly onto it so it "thinks" the house is warm? Let us know if you find the problem/solution.

What size is your home? How did you heat before this install? It appears you have a 3 ton HP condenser. What inside supply temp are you getting and note the outside temp at that time?

IMO

Certainly if the system isn't working properly, then the installer needs to correct it, but I don't think an overnight temperature of 56 is that terrible. If you have no recourse through the installer, then using a resistance heater for the few times you need more heat might be the cheapest solution. What's the coldest it ever gets in your part of Seattle?

The outdoor design temperatures for the Seattle area are about 26F degrees in the winter, and 82F degrees in the summer. Heat pumps should be sized for the cooling load. The 36K BTU size you have may be enough to cool your house to 75F degrees in the summer. It is hard to tell without knowing the size of the house and some basic insulation properties. However the heat pump is probably too small to heat the house to 72F degrees on a 30F degree night. This is especially true if you have old drafty windows. The difference between the house's heat loss and the heat pump's output has to be made up by the back up electrical heat.

It sounds like there you have an installation problem. You also need to verify the backup heat is properly sized and working when it is needed. You should ask the installer when does the back up heating turn on if the heat pump cannot provide heat on very cold nights.

Thanks everyone, here's a little more info about my case:

• Home is 3500 sqft in total but this system is only for the main level, the basement has underfloor gas powered heating. Roughly 2000 sqft on the main level.
• No backup heat in the heat pump, it doesn't have hyper heat.
• It's the only heating mechanism on the main level other than the fireplace in the living room. The house used to have baseboard radiators from old oil heating but we pulled them out as part of our remodel.
  -Seattle doesn't really get much colder than 30F, it's back up to warmer and wetter nights now but we do get about a week or two of snow in early spring.
  -When the house was 56F inside and about 30F outside, the air coming from the registers was topping out at 75F. Felt cold to the touch but used a food thermometer to check.
• The thermostat is installed near the return so not near the registers.

It's 40F outside right now and the house is sitting at 69F with the thermostat set to 70F. So when the temperature outside is up, it has no trouble meeting the requested temperature, even with the leaky windows.
I have a technician coming tomorrow, thanks for helping me understand what I should ask about. Any more tips would be great!

Supply temp?

tigerdunes, if you mean the temperature of the air in the vent at the register, it was 75F when 30F outside. It's 70F inside now and 43F outside with air supply temp at 87F from the vents.

Is the duct work in the attic? If so do you know if R8 insulated flexible ducts were used?

I have never owned a heat pump, but I would be disappointed of the supply vents were only 75F degrees when the outdoor temperature is only 30F degrees. I suspect there are installation problems which still need to be addressed.

Just to keep this thread updated, after the technician found the issue, their sales rep was sent out to tell us that since we declined the hyper heat option when they presented us with options first day, they'll now upgrade the system to hyper heat for a fee of $6k. After we already paid $30k for the system that isn't working properly.

I'm incredibly disappointed that the company put this poorly designed system on us and are claiming we're deciding to upgrade instead of admitting that they messed up. We declined hyper heat because we were told it's for colder parts of the US and that both heat pumps produce the 36k BTUs needed to power both 18k units in our attic. Now they're pretending we made an informed decision to get the heat pump that doesn't work properly with our indoor units. We should never have been presented with options that wouldn't work.

I refused their offer of $6k followed but an offer of $5k and waiting for them to accept fault and make it right. The technician told us they got it wrong and now they're trying to gaslight us rather than own their mistake. I'm quite upset about this. I'll keep this thread updated.

Who told you that hyper heat was only necessary in colder areas - the installing company? Hyper heat (which I guess is resistance heat) is only used when it gets colder, but is a necessary backup. I would think that a heat pump large enough to heat your house from 25F is oversized, and more expensive than the resistance heat option.

mtvhike, it was the Sales guy for the HVAC company. There's so much marketing around Hyper Heat that it's hard to clearly find what it is but it does run only when the temperature drops from what I understand.

Have a call with the company today, hoping for a good outcome.

We were once again offered $5k or they can pull out the whole system and exercise our return policy. There is only $1k of a difference in the pumps which we have offered to pay but I don't accept that we should have to pay for more.

I've asked to speak to management. This is ridiculous. Why bother sending out engineers to diagnose a problem if you won't take responsibility when the result doesn't suit you?!

Sounds to me like they dropped the ball in installing this machine. The description shows this machine to be an inverter driven / multi zone heat pump with heating capable down to 5F.

Your climate (Seattle) is very well situated for heat pump operation. Provided of course you hire someone that actually knows what they are doing. That is always the con in much of this.

Information specifics about your system model.

I service the Katy, Texas area.

Took some time but I'm back with a positive update :)

A manager from the company came out to chat with us and admitted they made a mistake. The heat pump was replaced for a hyper heat version with a branch box at just the cost of the hardware difference.

Initial tests by the installers showed a 25F increase in heat coming from the vents when compared to the older one.

Thanks all for your support, I feel like we have the right system for our home now.

Hi. I'm in the Seattle area and considering a heat pump. I've recieved a quote for the Mitsubishi hyper-heating system. Like you originally, I'm wondering if I needed hyper-heating since it rarely drops into the 20s here. Would love an update on your sitch and find out which company you used. Would like to avoid the trouble you went through! Would you mind sharing?

The real question is what would be the indoor temperature when the out side is at it's lowest (I assume 20F or less). If you can't live with that, then install the resistance backup. The downside of resistance heat is it's operating cost, but if you're using it only a few times a year, that would be much less than the cost of a larger system.

Resistance heat is just a couple of electric heating elements (wires). There should be minimal additional cost to including this in a new system.