Heat pumps and additions

[Anonymous]

Adding about 1200 sf on our house and changing the vents so upstairs and downstairs will have separate controls. Is a heat pump usually enough in this situation or do we need another HVAC?

[Anonymous]

We have this situation -- regular gas furnace downstairs, heat pump upstairs. I won't lie to you -- when it gets super cold, the heat pump can't keep up and it switches to regular electric heat, which is very expensive.

I would do all the insulating and energy planning you can for the addition. You will find that adjusting the downstairs can help the upstairs, since heat rises. Also pay attention to thermostat location -- ours is in the hall at the top of the stairs, so it registers the heat rising from downstairs and thinks it's warm enough, but meanwhile our bedrooms are cold.

If I had it to do again, I would hire an energy consultant to help plan the addition.

[Anonymous]

Modern efficient heat pumps are fine for additions in this area, especially if they are open to original and get the benefit from some of the forced air gas heat. And by the way, a heat pump is HVAC. The electric supplement on a heat pump is fairly efficient these days too.

The alternative is to have an AC unit (basically the same thing as a heat pump) AND a conventional furnace. So it is double the cost, for very little benefit.

Agree with PP on correct thermostat placement being of paramount importance.

[Anonymous]

Anonymous wrote:We have this situation -- regular gas furnace downstairs, heat pump upstairs. I won't lie to you -- when it gets super cold, the heat pump can't keep up and it switches to regular electric heat, which is very expensive.

I would do all the insulating and energy planning you can for the addition. You will find that adjusting the downstairs can help the upstairs, since heat rises. Also pay attention to thermostat location -- ours is in the hall at the top of the stairs, so it registers the heat rising from downstairs and thinks it's warm enough, but meanwhile our bedrooms are cold.

If I had it to do again, I would hire an energy consultant to help plan the addition.

+1 on all of this. Heat pumps do not work well in cold weather. No it doesn't get that cold here that often, but when it does...that's when you want the heat to be working and not costing a fortune. We have a heat pump for our upstairs and gas for downstairs. Gas is a lot cheaper.

Don't put your thermostat in the hallway for the reason PP said. We have the same problem.

[Anonymous]

Anonymous wrote:

Anonymous wrote:We have this situation -- regular gas furnace downstairs, heat pump upstairs. I won't lie to you -- when it gets super cold, the heat pump can't keep up and it switches to regular electric heat, which is very expensive.

I would do all the insulating and energy planning you can for the addition. You will find that adjusting the downstairs can help the upstairs, since heat rises. Also pay attention to thermostat location -- ours is in the hall at the top of the stairs, so it registers the heat rising from downstairs and thinks it's warm enough, but meanwhile our bedrooms are cold.

If I had it to do again, I would hire an energy consultant to help plan the addition.

+1 on all of this. Heat pumps do not work well in cold weather. No it doesn't get that cold here that often, but when it does...that's when you want the heat to be working and not costing a fortune. We have a heat pump for our upstairs and gas for downstairs. Gas is a lot cheaper.

Don't put your thermostat in the hallway for the reason PP said. We have the same problem.

+2

Thermostat is in our bedroom but it still isn't as warm as I like on these frigid days.

On another vote -- my HVAC tech friend doesn't agree, but I do think the heat pump coupled with the newer building materials is a recipe for disaster. I mean, wouldn't it make sense that the original part of the house, which is brick and plaster, holds in heat better than drywall and siding?

[Anonymous]

Does anyone have strategies to balance it out?

I have gas on the lower level and heat pump upstairs.

Is it better to just run the gas on the first floor and not turn it down at night?

[Anonymous]

Anonymous wrote:Does anyone have strategies to balance it out?

I have gas on the lower level and heat pump upstairs.

Is it better to just run the gas on the first floor and not turn it down at night?

If you do that, you will end up colder because the thermostat will register that extra heat and not turn on the heat pump often enough.

[Anonymous]

Anonymous wrote:

+2

Thermostat is in our bedroom but it still isn't as warm as I like on these frigid days.

On another vote -- my HVAC tech friend doesn't agree, but I do think the heat pump coupled with the newer building materials is a recipe for disaster. I mean, wouldn't it make sense that the original part of the house, which is brick and plaster, holds in heat better than drywall and siding?

No, this isn't the way insulation works. A home framed with 2x4's using old insulation maybe achieves a R10 (new fiberglass is R15.) new construction using 2x6 framing gets a R21 rating using fiberglass. Add on that newer construction also tends to use better insulation than the cheapest fiber out there are the difference can be substantial. R values for brick are around 0.5. Fiber cement is about 0.20. Plaster and drywall have basically no insulative value.

Heat pumps with new construction are almost always the most cost-effective and efficient solution. And yes, they need to have good auxiliary heating elements for the 10 days a year the temp drops below about 19 degrees during the day.

[Anonymous]

Anonymous wrote:

Anonymous wrote:

+2

Thermostat is in our bedroom but it still isn't as warm as I like on these frigid days.

On another vote -- my HVAC tech friend doesn't agree, but I do think the heat pump coupled with the newer building materials is a recipe for disaster. I mean, wouldn't it make sense that the original part of the house, which is brick and plaster, holds in heat better than drywall and siding?

No, this isn't the way insulation works. A home framed with 2x4's using old insulation maybe achieves a R10 (new fiberglass is R15.) new construction using 2x6 framing gets a R21 rating using fiberglass. Add on that newer construction also tends to use better insulation than the cheapest fiber out there are the difference can be substantial. R values for brick are around 0.5. Fiber cement is about 0.20. Plaster and drywall have basically no insulative value.

Heat pumps with new construction are almost always the most cost-effective and efficient solution. And yes, they need to have good auxiliary heating elements for the 10 days a year the temp drops below about 19 degrees during the day.

Don't forget that new construction has Tyvek and often plastic wrap so that it's even more sealed from the outside.

[Anonymous]

Our old brick and plaster colonial has dreadful insulation. Anything new would have to be better unless the builder uses old newspapers.

[Anonymous]

Anonymous wrote:Our old brick and plaster colonial has dreadful insulation. Anything new would have to be better unless the builder uses old newspapers.

On our old home we actually found 1950s newspapers stuffed as insulation.

[Anonymous]

Note that auxiliary heat is expensive.

[Anonymous]

You or a contractor can do a heat load calculation and figure out if the heat pump will provide enough BTUs for your addition.

[Anonymous]

Anonymous wrote:Note that auxiliary heat is expensive.

What do you mean? That the heat pump will be expensive?

[Anonymous]

Heat pump output less heat the colder it is outside. Some have an 'auxiliary' which is essentially an electric heater. You lose the efficiency of a heat pump when that kicks on.