HVAC replacement - looking for advice from those who have BTDT

[Anonymous]

I highly recommend a subscription to Washington Checkbook. They've written in depth articles about HVAC systems so I knew what kind of equipment to ask for. I was surprised to find that a lot of providers simply qupted the cheapest equipment rather than take the time to educate me as a consumer in the hopes of upselling products. After reading through the options, I found that the higher end systems met our specific needs better.

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:I second the comment about variable stage (or multi-stage, or modulating). In my experience a modulating gas furnace and two-stage air conditioner made a big difference in comfort. Presumably heat pumps are available with similar. It eliminates the mentioned concerns about the system being oversized for some seasons, because it changes its capacity as needed.

I am not sure if this is true. My understanding is you lose the efficiency of the variable stage in the summer when it is oversized. Since it is oversized it can't run at the low level.that you actually need so it will shut on and off like a single stage. In addition to costing you more in electricity bills it won't do as good s job removing humidity.

I didn't mean to imply that proper system sizing doesn't matter. I meant that caveats about heat pump capacity in summer vs. winter aren't relevant, because the system has more ability to adapt itself to conditions.

I'm sorry, I'm not following. You are saying it's "not relevant" if a variable stage system is properly sued for heating but oversized for cooling? Why not? You are paying so much for the variable stage but o let getting the benefits in the winter.

If I understand what you’re saying, I guess the solution is a heat pump with more than 2 stages, or an inverter heat pump which is in effect infinitely variable.

You are assuming that an inverter heat pump's capacity can go all the way down to zero, and that's not accurate.

https://www.linkedin.com/posts/allisonabailes_can-you-oversize-a-mini-split-heat-pump-activity-7105132985556889600-d5Ss?utm_source=share&utm_medium=member_desktop

On the 2-stage A/C I had in my previous home, 1st stage capacity was 2/3 of 2nd stage. So if a unit was oversized, but could go down to 30% of full capacity, then it could have a 1st stage with a ratio similar to my A/C's. If you're mainly concerned with heat pump overcapacity during heating season, then the BTU output of the stages of a 2-stage gas furnace would be more relevant. I don't know what that is, because I had a modulating gas furnace.

Right, but then you've just paid extra for a two-stage AC that acts like a single-stage AC. It's less efficient and worse at dealing with humidity.

[Anonymous]

No one chooses a heat pump. If you buy a condo/townhouse that has one, then yes, replacing it with another is a reasonable decision. Otherwise, people in the DMV (due to the climate) do not convert another system to the less-desirable heat pump

[Anonymous]

Anonymous wrote:No one chooses a heat pump. If you buy a condo/townhouse that has one, then yes, replacing it with another is a reasonable decision. Otherwise, people in the DMV (due to the climate) do not convert another system to the less-desirable heat pump

This is not true. I see that the anti-heat pump troll has returned. Welcome back buddy.

[Anonymous]

Something you have to realize in these discussions: every house is unique. Every house is hand built. There is no such thing as a "normal" or "average" house.

As to the questions on sizing and heating vs. cooling, there are no rules of thumb. In our climate some houses are heating dominant, some are cooling dominant. Proper sizing of equipment involves doing what's called a "Manual J," which is a computer model of the energy use of your house. Code now requires it in most places. Doing a proper Manual J means going into every room in the house, measuring the dimensions of every room and all the windows and exterior doors. Also going into the attic and basement and looking at the construction. If someone wants to quote you a system without doing a Manual J, they're just guessing. Even if they just want to replace existing equipment with a similar size. In fact, especially if that's what they want to do.

The Manual J uses what's called the "design temperature," which is basically the hottest and coldest temperature we regularly see. In Washington, DC, the design temperature for heating and cooling are 21F and 92F.

Since the cooling temperature is only 20F from room temperature and the heating temperature is 50F, you'd think we'd need much more heating than cooling. But this is where the uniqueness of houses comes in. As part of the Manual J you have to figure out the solar gain and account for it. That means measuring the dimensions and orientation of every window in the house, and factoring in the solar gain factor for the type of glass in it. These aren't hard calculations, but it is work. You also have to figure the removal of humidity in the summer, which takes cooling capacity.

I had a Manual J done for my house. The results were that the heating load is 27,600 BTU/hr, and the cooling load is 29,800 BTU/hr. This is Washington, DC. The solar gain is almost half of the cooling load, 14,000 BTU/hr. I have lots of windows and my house faces south.

As part of the process I had the air infiltration of my house measured, using what's called a blower door test, a fan is mounted in the front door and pressure and flow are measured. My house is much tighter than most. This means that air infiltration is low, which means that I need less dehumidification in the summer than typical.

In my case, since the loads are so close, a heat pump sized for my winter heating load keeps the house comfortable year-round.

But every house is unique.

[Anonymous]

PP here: in lieu of a complete Manual J, the process in this article outlines how to use your actual energy usage to size equipment:
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

But if a guy wants to install equipment without either doing a full Manual J or analyzing at least a year's worth of energy bills, he's not someone you want to work with.

[Anonymous]

Anonymous wrote:

Anonymous wrote:No one chooses a heat pump. If you buy a condo/townhouse that has one, then yes, replacing it with another is a reasonable decision. Otherwise, people in the DMV (due to the climate) do not convert another system to the less-desirable heat pump

This is not true. I see that the anti-heat pump troll has returned. Welcome back buddy.

Insulting other posters doesn’t make your post correct. Explain why it’s not true instead. Be useful.

-np

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:No one chooses a heat pump. If you buy a condo/townhouse that has one, then yes, replacing it with another is a reasonable decision. Otherwise, people in the DMV (due to the climate) do not convert another system to the less-desirable heat pump

This is not true. I see that the anti-heat pump troll has returned. Welcome back buddy.

Insulting other posters doesn’t make your post correct. Explain why it’s not true instead. Be useful.

-np

DP: PP said "No one chooses a heat pump." I chose a heat pump. His blanket statements were incorrect and not helpful.

[Anonymous]

Anonymous wrote:PP here: in lieu of a complete Manual J, the process in this article outlines how to use your actual energy usage to size equipment:
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

But if a guy wants to install equipment without either doing a full Manual J or analyzing at least a year's worth of energy bills, he's not someone you want to work with.

Manual J is not required in Maryland, and you'll have a lot of trouble finding a contractor that will do it.

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:No one chooses a heat pump. If you buy a condo/townhouse that has one, then yes, replacing it with another is a reasonable decision. Otherwise, people in the DMV (due to the climate) do not convert another system to the less-desirable heat pump

This is not true. I see that the anti-heat pump troll has returned. Welcome back buddy.

Insulting other posters doesn’t make your post correct. Explain why it’s not true instead. Be useful.

-np

Don't act like a school teacher. PP's blanket statement that no one chooses a heat pump in the DMV is obviously false. Moreover, there is a frequent anti-heat pump troll that comes in whenever heat pumps are discussed. If you also believe that heat pumps don't work in cold weather, the State of Maine disagrees. https://www.bloomberg.com/news/articles/2023-10-06/how-maine-became-the-heat-pump-capital-of-the-us

[Anonymous]

-Heat pumps are work fine here; the old single stage ones can have trouble keeping up when it drops into the teens. They have backup electric heaters for a reason. We don't experience sustained cold temperatures that would knock out an inverter here.

-Not sure of a jurisdiction in MD that doesn't require Manual J or an equivalent heat load calc to issue permits for new construction. Retrofits are hit or miss; we do them for all our installs because having to rip out and reinstall incorrectly sized equipment is a fools errand.

-Everyone wants heat pumps. Up until 2022 our installs where 45% HP; 50% Nat Gas; and 5% Oil or Propane like clockwork. This year 90% of my jobs have included a heat pump. Most are still keeping fossil fuel as a backup but they don't want to use it as a primary heating source.

[Anonymous]

Anonymous wrote:-Heat pumps are work fine here; the old single stage ones can have trouble keeping up when it drops into the teens. They have backup electric heaters for a reason. We don't experience sustained cold temperatures that would knock out an inverter here.

-Not sure of a jurisdiction in MD that doesn't require Manual J or an equivalent heat load calc to issue permits for new construction. Retrofits are hit or miss; we do them for all our installs because having to rip out and reinstall incorrectly sized equipment is a fools errand.

-Everyone wants heat pumps. Up until 2022 our installs where 45% HP; 50% Nat Gas; and 5% Oil or Propane like clockwork. This year 90% of my jobs have included a heat pump. Most are still keeping fossil fuel as a backup but they don't want to use it as a primary heating source.

Most contractors are discouraging heat pumps because they cost more money overall and then you have higher electricity bills.

[Anonymous]

Anonymous wrote: we do them (Manual J) for all our installs because having to rip out and reinstall incorrectly sized equipment is a fools errand.

You want a contractor who says things like this.

First, they're up on the latest science. Second, they intend to stand by their work.

Question for PP: How do you integrate the Manual J into the bid process? Because I'd imagine a proper Manual J takes about $500 worth of labor. Do you bid just the labor of the install and say equipment is contingent on the results of the J? Or do you charge up front for the J?

[Anonymous]

Anonymous wrote:

Anonymous wrote: we do them (Manual J) for all our installs because having to rip out and reinstall incorrectly sized equipment is a fools errand.

You want a contractor who says things like this.

First, they're up on the latest science. Second, they intend to stand by their work.

Question for PP: How do you integrate the Manual J into the bid process? Because I'd imagine a proper Manual J takes about $500 worth of labor. Do you bid just the labor of the install and say equipment is contingent on the results of the J? Or do you charge up front for the J?

Thanks for asking this because even if the Manual J is required for the permit, it's not required to provide a quote. I understand why contractors don't want to do this for someone who is getting multiple quotes.

[Anonymous]

Anonymous wrote:Something you have to realize in these discussions: every house is unique. Every house is hand built. There is no such thing as a "normal" or "average" house.

As to the questions on sizing and heating vs. cooling, there are no rules of thumb. In our climate some houses are heating dominant, some are cooling dominant. Proper sizing of equipment involves doing what's called a "Manual J," which is a computer model of the energy use of your house. Code now requires it in most places. Doing a proper Manual J means going into every room in the house, measuring the dimensions of every room and all the windows and exterior doors. Also going into the attic and basement and looking at the construction. If someone wants to quote you a system without doing a Manual J, they're just guessing. Even if they just want to replace existing equipment with a similar size. In fact, especially if that's what they want to do.

The Manual J uses what's called the "design temperature," which is basically the hottest and coldest temperature we regularly see. In Washington, DC, the design temperature for heating and cooling are 21F and 92F.

Since the cooling temperature is only 20F from room temperature and the heating temperature is 50F, you'd think we'd need much more heating than cooling. But this is where the uniqueness of houses comes in. As part of the Manual J you have to figure out the solar gain and account for it. That means measuring the dimensions and orientation of every window in the house, and factoring in the solar gain factor for the type of glass in it. These aren't hard calculations, but it is work. You also have to figure the removal of humidity in the summer, which takes cooling capacity.

I had a Manual J done for my house. The results were that the heating load is 27,600 BTU/hr, and the cooling load is 29,800 BTU/hr. This is Washington, DC. The solar gain is almost half of the cooling load, 14,000 BTU/hr. I have lots of windows and my house faces south.

As part of the process I had the air infiltration of my house measured, using what's called a blower door test, a fan is mounted in the front door and pressure and flow are measured. My house is much tighter than most. This means that air infiltration is low, which means that I need less dehumidification in the summer than typical.

In my case, since the loads are so close, a heat pump sized for my winter heating load keeps the house comfortable year-round.

But every house is unique.

OP's house is 70 years old. It's true that new builds may have very similar heating and cooling loads. Unlikely that's the case for OP.